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NCERT Solutions For Class 8 Science Chapter 2 Microorganisms

NCERT Solutions for  Class 8 Science Chapter 2, provided on this page, is prepared by subject matter experts. Students can use these solutions during revision to understand the concepts of the chapter better.

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June 7, 2024

assignment of microorganisms class 8

Table of Contents

NCERT Solutions for Class 8 Science Chapter 2: gives a thorough knowledge of microorganisms and their various functions and activities. To help students improve their understanding of the fundamentals, our team of subject experts has prepared solutions for the different questions in this chapter, considering the CBSE board’s requirements. Students can consult the NCERT solutions for Class 8 Science Chapter 2 for effective exam preparation and positive outcomes.

CBSE Class 8 Science Syllabus

NCERT Solutions for Class 8 Science Chapter 2 Overview

NCERT Class 8 Science Chapter 2 thoroughly examines the various functions that microorganisms perform in ecosystems and our daily lives. The chapter highlights the useful functions of microbes, including their importance to environmental processes.

The detrimental effects of some microbes, referred to as pathogens, which cause illnesses in people, animals, and plants, are also covered in this chapter. The NCERT solutions  Class 8 Science Chapter 2 questions in this article will help students understand the important topics and answer the questions accurately in exams.

List of the Topics Covered in NCERT Class 8 Science Chapter 2 

The different topics covered in NCERT Class 8 Science Chapter 2 are discussed below:

  • Microorganisms
  • Habitats of Microorganisms
  • Microorganisms and us
  • Harmful microorganisms
  • Food preservation
  • Nitrogen fixation
  • Nitrogen cycle

NCERT Solutions for Class 8 Science Chapter 2 PDF

For the convenience of the students, we have provided the NCERT Solutions For Class 8 Science Chapter 2 in PDF format below. Students can download it using the given link and study thoroughly to understand the topics covered in the chapter.  

NCERT Solutions for Class 8 Science Chapter 2 Exercise Questions

Fill in the blanks:

(a) Microorganisms can be seen with the help of a ____________.

(b) Blue-green algae fix __________ directly from the air and enhance the fertility of the soil.

(c) Alcohol is produced with the help of __________.

(d) Cholera is caused by __________.

Solutions: 

  • a) Microscope
  • b) Nitrogen
  • d) Bacteria ( Vibrio cholera) 
  • Tick the correct answer.

(a) Yeast is used in the production of

(i) sugar; (ii) alcohol; (iii) hydrochloric acid; (iv) oxygen

(b) The following is an antibiotic:

(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) yeast

(c) The carrier of a malaria-causing protozoan is

(i) female Anopheles mosquito; (ii) cockroach; (iii) housefly; (iv) butterfly

(d) The most common carrier of communicable diseases is

(i) ant; (ii) housefly; (iii) dragonfly; (iv) spider

(e) The bread, or idli dough, rises because of

(i) heat; (ii) grinding; (iii) growth of yeast cells; (iv) kneading

(f) The process of converting sugar into alcohol is called

(i) nitrogen fixation; (ii) moulding; (iii) fermentation; (iv) infection

  • a) (ii) alcohol
  • b) (ii) Streptomycin
  • c) (i) female Anopheles mosquito
  • d) (ii) housefly
  • e) (iii) growth of yeast cells
  • f) (iii) fermentation
  • Match the organisms in Column A with their actions in Column B.
Bacteria Fixing Nitrogen
Rhizobium Fixing of curd
Lactobacillus Baking of bread
Yeast Causing Malaria
Protozoa Causing Cholera
A Virus Causing AIDS
Producing Antibodies
Bacteria Causing Cholera
Rhizobium Fixing Nitrogen
Lactobacillus Setting of Curd
Yeast Baking of Bread
Protozoa Causing Malaria
A Virus Causing AIDS
Producing Antibodies
  • Can microorganisms be seen with the naked eye? If not, how can they be seen?

Microorganisms are tiny, so they can’t be seen with the naked eye. Some fungus growth on bread can be seen with a magnifying glass. A powerful microscope is used to see the microorganisms clearly.

  • What are the major groups of microorganisms?

The major groups of microorganisms include:

  • Name the microorganisms that can fix atmospheric nitrogen in the soil.
  • Write 10 lines on the usefulness of microorganisms in our lives.

Some of the usefulness of microorganisms in our lives is mentioned below.

  • Lactobacillus-type bacteria use milk to make curd.
  • Cheese is also made with the help of bacteria.
  • The bacteria Acetobacter aceti produces acetic acid from alcohol.
  • Commercial manufacturing of wine, beer, and baked goods all employs yeast.
  • Bacteria and yeast are used for the fermentation of rice idlis and dosa batter.
  • Certain bacteria are useful in the production of antibiotics.
  • Microorganisms break down waste materials into manure and serve as cleaning agents.
  • Vaccines are made with either dead or weakened microorganisms.
  • Certain microorganisms improve soil fertility by removing nitrogen from the atmosphere.
  • Algae, yeast, fungi, or bacteria can be utilized as components to make foods high in protein suitable for human or animal consumption.
  • Write a short paragraph on the harmful effects of microorganisms.

Microorganisms can harm us in some ways. For instance, pathogens are microbes that cause human, plant, and animal diseases. Viruses are the source of many common illnesses, such as chicken pox, polio, cough, and influenza. Bacteria cause tuberculosis, typhoid, and the deadly animal and human disease anthrax. Protozoa produce diseases, including malaria and dysentery. Furthermore, food deterioration and food poisoning are caused by microorganisms.

  • What are antibiotics? What precautions must be taken while taking antibiotics?

Antibiotics are drugs used to treat a disease by eradicating or preventing the growth of microorganisms that cause the illness. Only a licensed medical professional should prescribe antibiotics. One must also finish the course as prescribed by the doctor.

Benefits of Referring To NCERT Solutions for Class 8 Science Chapter 2

  • Effective Exam Preparation: The solutions for NCERT Class 8 Science Chapter 2 are prepared by experts, considering the latest CBSE syllabus requirements. It will help students thoroughly understand the concept, making exam preparations more effective.
  • Easy to Understand and Recall: Academicians with subject-matter expertise wrote the NCERT Class 8 Science solutions very fluently and straightforwardly, making it simple for students to understand and remember the answers.
  • Quick Revision: The NCERT solution for Class 8 Science chapter 2 exercise helps students quickly go through the important points of the various topics of the chapter during the revision process and also helps them answer other questions during practice.

NCERT Solutions For Class 8 Science Chapter 2 FAQs

Ans. The presence of oil or vinegar prevents the growth of microorganisms that can spoil the material.

Ans. The milk is heated to 70 degrees Celsius, then chilled suddenly and stored. This process is known as pasteurization, which prevents the growth of microbes in milk.

Ans. The harmful microorganisms, or pathogens, can be transmitted by direct contact with the infected person, by transmission through air, water, or food, or through insects and other animals.

. Vaccines are prepared from dead or weakened microbes that are inserted into the human body to stimulate the immune system to produce antibodies, which can defend the body from the effects of microbes. These antibodies remain in the body and help fight further infections caused by microbes.

Ans. Microorganisms can live in a diverse range of environments, both hot and cold. They are also found inside animal bodies, including those of humans.

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Revision Notes For CBSE Class 8 Science Chapter 2- Microorganisms: Friends And Foe

  • Revision Notes
  • Chapter 2 Microorganisms: Friend And Foe

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Class 8 Science Friends And Foe Revision Notes: Free PDF Download

Science in Class 8 is the foundation topic that students learn before moving on to Secondary Level schooling. The second chapter of the CBSE Class 8 Science syllabus is on microorganisms. Students will study if microbes are our allies or foes in this lesson. You may tell by the title that this chapter will talk about microorganisms that aid us and those that cause sickness. There is a lot of new material to comprehend and remember in this chapter.

To make it easier for the Class 8 students, the experts of Vedantu have developed Class 8 Science Chapter 2 notes to follow. In these notes, you will find an excellent explanation of all the chapters in a simpler language. These notes will help you understand the new side of the world of microorganisms. You can download these revision notes and store them on your smart devices for offline access. These notes can be perfectly used to recapitulate the chapter before an exam. Download Microorganisms Friend and Foe Class 8 notes for free and use it to study the chapter well.

Vedantu also provides CBSE NCERT Solutions for all subjects and classes for free.You can also Download NCERT Solution for Class 8 Maths and NCERT Solutions for Class 8 Science to help you to revise the complete syllabus and score more marks in your examinations.

Topics Covered In Class 8 Science Chapter 2

2.1

Microorganisms

2.2

Where do Microorganisms live?

2.3

Microorganisms And Us

2.4

Harmful Microorganisms

2.5

Food Preservatives

2.6

Nitrogen Fixation

2.7

Nitrogen Cycle

Download CBSE Class 8 Science Revision Notes 2024-25 PDF

Also, check CBSE Class 8 Science revision notes for other chapters:

CBSE Class 8 Science Chapter-wise Notes

Chapter 2: Microorganisms: Friends and Foe Notes

Access Class 8 Science Chapter 2 - Microorganisms: Friend and Foe

Micro-organisms: , there are numerous organisms living around us that we may not be able to see. we can see some of them through a magnifying glass, like the fungus on bread. some others are so small that they cannot be seen without a microscope.  these organisms that cannot be seen by unaided eyes are termed microorganisms or microbes. the microorganisms can be broadly classified as: bacteria - they are a group of prokaryotic organisms (does not have membrane-bound nucleus or organelles) that constitute a major part of microorganisms. they can inhabit soil, water, and every other habit found on earth. they can be a few micrometers in length and can be of various shapes like spheres, rods, or spirals. example - escherichia coli, coliform bacteria, etc.  fungi - they are a group of eukaryotic organisms (have a membrane-bound nucleus and organelles) that are usually heterotrophic in nature. examples - penicillium, bread mold, mushroom, etc. protozoa - they are a group of unicellular eukaryotic organisms that may be parasitic or living independently and are heterotrophic (cannot prepare their own food) in nature. example - amoeba, paramecium, etc. algae - they are a group of photosynthetic eukaryotic organisms that are predominantly aquatic. example - spirogyra, chlamydomonas, etc. these groups of microorganisms may be harmful or useful in nature. (image will be uploaded soon) the virus is also a microorganism, but they differ from the others in this group as they can reproduce only in the body of a host, be it animals, plants, or humans. example - aids, herpes, rubella, zika, etc., where do microorganisms live, the microorganism may be single-celled or unicellular as in bacteria, protozoa or they may be multicellular as in fungi, animals, etc.  they can survive in water, air and all kinds of environmental conditions like extreme cold climate to even the hot springs, deserts, and marshy lands. some of them even live inside the body of animals, and even humans.  some of them grow on their own whereas others thrive on the body of other animals. , microorganisms and us:, it is to be noted that these microorganisms play a vital role in our lives. some of them may be beneficial to us whereas some of them may have an adverse and harmful effect on us., friendly use of microorganisms:, microorganisms can be put to multiple uses, be it in the making of alcohol, bread, cake, or medicines or in agriculture or cleaning the environment.  (image will be uploaded soon) making of curd and bread:   a bacterium, namely lactobacillus, multiplies in milk converting it into curd. the making of cheese, pickles, and various other food products also involve the use of bacteria.  the process of fermentation [conversion of sugar to alcohol] that is required in the rice batter for making idlis and dosa is again helped by bacteria and yeast.  when yeast is added to a dough, it reproduces rapidly releasing carbon dioxide which bubbles into the dough, making it rise. this property of yeast is used to make bread, cakes, etc. commercial use of microorganisms:   yeast is an ingredient that is widely used in the production of alcohol, wine, and vinegar. this is done by growing yeast on the natural sugar present in the fruit juices like grapes, grains like barley, wheat, rice, etc.  the sugars are converted to alcohol by fermentation. medicinal use of microorganisms:   the source of the widely used medicines, antibiotics(medicines that stop or kill the disease-causing agents) are again microorganisms.  these are manufactured by growing specific as a cure for various diseases.  some of the antibiotics are streptomycin, erythromycin, azithromycin, etc. vaccine:  a disease-causing microorganism called a pathogen produces antibodies against it when it enters our body. these antibodies are retained in our body and we are protected from that disease forever.  a vaccine is a biological substance that initiates the production of antibodies for a specific disease. thus a vaccination protects us from that specific disease.  children are generally vaccinated for many diseases like polio, tuberculosis, chickenpox, hepatitis, etc. smallpox has been eradicated this way. and currently, the covid vaccine is doing the same. increasing soil fertility:  there are some bacteria, like rhizobium that are present in the soil, generally in the roots of leguminous plants, that are capable of fixing the atmospheric nitrogen to enrich the soil with nitrogen which increases the fertility of the soil and the yield of the crop. cleaning the environment:  some of the microorganisms have the ability to decompose dead organic matter and convert them into simpler substances or manure that can be reused for animals or plants, making the environment clean. , harmful uses of microorganisms:, they can be harmful in numerous ways to humans, plants, and animals and cause diseases. as stated, the disease-causing microorganisms are known by the name of pathogens.        (image will be uploaded soon) disease-causing microorganisms in humans:  the harmful pathogens enter the body of humans by means of air, water, or food. they can then spread to others by contact with the infected person or through an animal or insect. the diseases that can spread from an infected person to a healthy person by means of air, water, or contact are termed communicable diseases. examples - plague, chickenpox, tuberculosis, common cold, and the current covid 19 infections. these disease-bearing microorganisms are sometimes carried by insects and animals then they are termed as carriers of that disease. for example - the female anopheles mosquito is the carrier of plasmodium that causes malaria. the mode of transmission, type of microorganism, the disease caused by these microorganisms, and their prevention differ from each other as shown below: (image will be uploaded soon) the prevention of these diseases follows a general pattern of keeping the affected person and his belongings isolated, personal hygiene, proper sanitary practices, drinking boiled and clean water, controlling breeding sites of mosquitoes, consuming properly cooked food, and above vaccination against all these diseases on schedule. disease-causing microorganisms in animals:  many of the microorganisms are a cause of certain diseases in animals too. a few of the diseases found in animals is as shown below: (image will be uploaded soon) disease-causing microorganisms in plants:  many microorganisms are responsible for diseases in plants of potato, rice, wheat, sugarcane, etc reducing the quality and quantity of the yield of the crops. these diseases can be controlled by the use of chemicals that destroys these organisms. some of the diseases of plants are listed as below: (image will be uploaded soon) food poisoning: when the microorganisms contaminate the food, they sometimes produce toxic substances which leads to the ill health of a person consuming it and has health problems like vomiting and needs to be taken to a hospital. this condition of consuming food contaminated with microorganisms is called food poisoning. , preservation of food:, as discussed above, contamination of the food by microorganisms leads to a change in the color and taste of the food. several methods can be followed to prevent this microorganism attack some of them are as follows: a. chemical method: generally salts and edible oils are used to control their growth and these are termed preservatives. example - salt in pickles, sodium benzoate in jams. b. common salt: this is a common practice where meat and fish or some fruits like raw mangoes, tamarind, etc are covered with salt to last them for longer periods. c. sugar: some food items like jams and jellies are preserved in sugar which reduces the moisture to inhibit the growth of microorganisms. d. oil and vinegar: this is also used commonly as the microorganisms cannot live in such conditions. this is widely used in making pickles. e. heat and cold treatments: it is a common practice to boil milk in order to store it. the method of heating milk to eliminate the microbes present in it is called pasteurization. similarly storing food at low temperatures also prevents the growth of these microbes., nitrogen cycle:, the nitrogen cycle can be defined as a biochemical process of circulating the nitrogen in the atmosphere, through soil, organisms, and back to the atmosphere.  the nitrogen present in the atmosphere cannot be consumed by plants or animals directly. this nitrogen needs to be converted to nitrogenous compounds by some bacteria in the soil. this converted form of nitrogen is used by the plants and when the animals feed on them they get that. the fungi and bacteria in the soil convert the nitrogen present in dead plants and animals to either gaseous or compounds that are reused by the plants. thus the balance of nitrogen is maintained in the atmosphere. (image will be uploaded soon), a brief overview of class 8 chapter 2 microorganisms: friends and foe.

Microorganisms are everywhere. They remain invisible to our naked eyes. Some are good and some impart a threat to our health. In this chapter, we will learn more about the microorganisms that help us and those that cause diseases. This chapter will introduce you to four different types of microbes that are protozoa, fungi, bacteria, and algae. Refer to the Science Chapter 2 Class 8 notes to understand the concepts better.

The chapter begins with a proper introduction to the world of microbes. These organisms are everywhere around us and we cannot see them without the assistance of a microscope. On proceeding further in the chapter, you will find an extensive discussion related to bacteria. These are unicellular primitive organisms that have a prokaryotic nucleus. There are different kinds of bacteria present that either helps us or cause diseases. If you refer to the Microorganisms Class 8 notes, you will find out how bacteria can be used to escalate our health. For instance, it will discuss probiotics. It is a medicated solution of living yeasts and bacteria that can be directly consumed to restore balance in our digestive system.

Proceeding further, you will reach the fungi section. These are a little advanced than the bacteria and fall in the plant classification. These are parasitic and saprophytic organisms. These organisms are multicellular and can be seen with our naked eyes. Some of the fungal species exist in unicellular form. You will find excellent uses of fungi mentioned in this chapter. Use the Class 8 Chapter 2 Science notes to study this section and learn how fungi are used for fermentation. We use this process to produce alcohol and curd. Fungi are also used for different purposes. These revision notes will explain all these uses in a simpler language.

Protozoa, on the other hand, are single-celled microbes. They have a eukaryotic nucleus and fall in the animal kingdom. Protozoa can generally move with their cilia, flagella, etc. In this section, you will find how protozoa are harmful to our health. In Science Class 8 Chapter 2 notes, you will then proceed to the section describing viruses. These organisms are miracles of nature. These organisms show living characteristics inside a host cell but show no sign of life outside. The viruses impart harm by causing different diseases such as rabies, HIV, polio, etc.

Why Should You Follow Chapter 2 Science Class 8 Notes?

When you follow Chapter 2 Science Class 8 notes, you will discover a simple explanation of all the concepts mentioned in this chapter. It will help you understand how microbes can be useful to us. You will also find which microbes impart harm by causing disease. To get your revision done faster, download the Class 8 Science Ch 2 notes and use them as a reference before an exam.

Why Should You Opt for Vedantu’s Revision Notes For Class 8 Science Chapter 2?

Vedantu’s CBSE Revision notes for Class 8 Science Chapter 2 are the best online study materials in pdf format. The pdf covers the explanation of concepts in an easy-to-understand language and with diagrams wherever required to enable students to understand the concepts easily. Furthermore, the notes are provided concisely, allowing the students to recall and reinforce concepts at the last moment.

Important Questions For Practice

Very short answer type questions.

Name the four major groups of microorganisms.

Are viruses microscopic?

Where do microorganisms live?

Define fermentation.

Who discovered the smallpox vaccine and when?

Short Answer Type Questions

What are antibiotics?

What are communicable disease?

Name microorganisms that cause disease in plants and animals.

Name few common chemicals that are generally used to check the growth of the organisms.

What actions should be taken to prevent the communicable diseases?

Long Answer Type Questions

Explain Nitrogen Cycle with diagram.

What preventive measures should be taken if a person suffers from tuberculosis, cholera, hepatitis-A, and Malaria?

Explain the process of fermentation.

Last-minute revision from a textbook is not an easy task. Vedantu’s revision notes  for CBSE Class 8 Science Chapter 2 summarise important topics of a chapter in an easy-to-understand  format. They provide students additional reference to the chapter for preparing the chapter quickly and and help gain confidence before appearing for their examinations. Download the pdf and keep all the important topics of the chapter at your fingertips.

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FAQs on Revision Notes For CBSE Class 8 Science Chapter 2- Microorganisms: Friends And Foe

1. How are microorganisms used?

As per Class 8th Science Chapter 2 notes, microbes are used to make food products, prepare new medicines, and different bioactive molecules at a very low cost.

2. What are pathogens?

Pathogens are microorganisms that cause diseases in a host. They are generally parasites. Follow the notes of Science Class 8 Chapter 2 to find examples related to pathogens.

3. What are a carrier and a vector?

A carrier is someone who is carrying pathogens and contaminating others. A vector is a carrier of diseases that contaminates a disease by biting a host. Study Chapter 2 Class 8 Science notes to find out more differences between a carrier and a vector.

4. What are Microorganisms according to Chapter 2 of Class 8 Science?

Microorganisms, often known as microbes, are living organisms that are invisible to the naked eye. They are only visible using a magnifying glass or a microscope. Depending on the kind, microbes can be unicellular or multicellular. Microorganisms, as indicated in Chapter 2 of Science Class 8, can be both hazardous and useful. They may be found anywhere. There are certain exceptions, such as fungus and algae, which humans can see without any special equipment when they infect food.

5. Where do Microorganisms live according to Chapter 2 of Class 8 Science?

Microorganisms may exist in a variety of conditions. Some, such as algae, can be found in water. The air contains bacteria and viruses, many of which cause sickness. Microbes such as archaea, fungus, protists, and others have been discovered within human and animal bodies on rare instances. Some bacteria, but not all, are tolerant to severe circumstances such as cold, heat, a lack of water, a high salt content, and a lack of oxygen in the environment.

6. Is a microorganism a friend or foe according to Chapter 2 of Class 8 Science?

Microorganisms can be both a friend and an adversary, according to Chapter 2 of Science Class 8. Several microorganisms are utilised in cooking, commercial and medical purposes, soil fertilisation, and other applications. On the other hand, some microorganisms are the cause of illness in people, plants, and animals. It should be noted that microorganisms are as much a part of our environment as other living beings and hence, they have an impact on nature in different ways.

7. What are the characteristics of Microorganisms according to Chapter 2 of Class 8 Science?

Microorganisms are unicellular or multicellular organisms that cannot be seen by the naked eye. They are categorized into six major types as per their typical features: bacteria, protozoa, fungi, archaea, algae, and viruses. In the revision notes of Chapter 2 Class 8 Science provided by Vedantu , you can learn to distinguish between different kinds of microorganisms based on their peculiarities. You will also get a detailed understanding of the various uses of different microbes in this particular chapter.

8. What is the Nitrogen Cycle according to Chapter 2 of Class 8 Science?

The nitrogen cycle is the conversion of nitrogen in the environment into chemical forms. Plants require nitrogen to flourish, but they cannot take it directly from the air. Bacteria and green algae are microorganisms that help break down nitrogen and refill the soil with it. These nitrogen molecules are then utilised by plants, and through plants, they reach other living organisms. It is a natural procedure that does not need any deduction.

NCERT Solutions

Study materials for class 8.

assignment of microorganisms class 8

Microorganisms Class 8 Science Chapter 2 as per NCERT Book used in CBSE and other Schools. The lesson covers the complete explanation of class 8 Chapter 2 Microorganisms . Topics covered are Introduction to Micro-organisms and microbiology, different types of Micro-organisms, Useful and Harmful Micro-organisms. How to avoid the spreading of Microorganisms has been discussed. Conditions that promote Microorganisms and Preservation of Food have been explained too. The lesson covers all important questions based on microorganisms. NCERT solutions to book questions have also been provided for the convenience of the students.

Microorganisms Class 8 Video Explanation

The topics we will cover in this chapter are as follows:

  • Introduction of Micro-organisms and microbiology
  • Different types of Micro-organisms
  • Useful and Harmful Micro-organisms
  • Avoiding spreading of Micro-organisms
  • Conditions that promote Micro-organisms
  • Preservation of Food

There are various living organisms that exist on earth, but there are some organisms which cannot be seen with the naked eye while there are others which can be seen.

The living organisms that you fail to see with your eyes and which can be seen only with the microscope are called as micro-organisms . These microorganisms are very small and widely found. The study of microorganisms is known as microbiology . Most organisms are hardy and can be found in almost any kind of environment like hot deserts, polar ice caps, salt water, marsh lands and inside other organisms.

The knowledge of their existence came after the discovery of cells by Robert Hooke in 1665.

After the discovery of cells Anton van Leeuwenhoek was able to identify the first living cell in a drop of water. Anton van Leeuwenhoek discovered the microscope and microorganisms, more precisely microscopic bacteria. Later on in 1857 Louis Pasteur laid the foundation of microbiology.

Microbiology

louis pasteur

A vaccine typically contains an agent that is similar to a disease-causing microorganism. It is often made from weakened or killed forms of the microbe and injected into the body as per our need. Therefore, we can say that vaccines are helpful to keep us healthy and protect us from infections. Vaccines provide immunity or power inside the body, which means that it makes our body resistant to microorganisms or any infection.

Now the question arises where do these microorganisms live?

Answer: Microorganisms have flexible adaptability, that means they can survive in almost all areas or environments. They can survive under all types of environmental conditions ranging from ice cold to hot springs and deserts to marshy lands. These microorganisms are also found inside the human bodies. Some microorganisms grow on other organisms, some of them exist freely, some of them live alone, and some microorganisms live in colonies, which means that microorganisms live with similar communities. They are also found inside the bodies of animals including humans, air, water, soil, food and other things.

Question: Can microorganisms be seen with the naked eye? If not, how can they be seen?  Answer: Microorganisms are too small. So, they cannot be seen with the naked eye. To see the microorganisms like bacteria and protozoa, we use a microscope. Fungus that grows on the bread can be seen with a magnifying glass.

Types of Microorganisms

There are of five types of microorganisms, as follows-

Let us discuss them in detail-

image12

  • They are unicellular microorganisms. They are mostly single- celled tiny organisms, but they live together in colonies of millions. Bacteria is to be seen under microscope which enlarges their size from a hundred to thousand times.
  • They do not have well defined nucleus. It contains ribosomes and plasmids. This plasmid is helpful in reproduction.
  • The size of bacteria ranges from 0.2 micron to 100 microns.
  • Smallest bacteria has a size of 0.15 micron.
  • Largest bacteria is 1.5 micron in size.
  • Some bacterias are aerobic, which means they respire in the presence of oxygen and some of them are anaerobic, which means that they does not respire in the presence of oxygen.
  • They are divided into four types depending upon shapes:

Cocci: This means that bacteria is circular or spherical in shape.

Bacillus: This means that bacteria is rod-shaped.

Spirilum: This means that bacteria is in spiral shape.

Vibrio: This means that bacteria is in comma like shape.  

image13

  • Virus cannot be seen with simple microscope. Though, it is a microorganism, and we know that microorganisms can be seen with a simple microscope, but virus cannot be seen under a microscope.
  • To see them, a powerful microscope is needed.
  • Viruses are the smallest of all microorganisms.
  • They consist of nucleic acid covered with protein shell.
  • Some viruses are living and some are non living. They are considered living when present inside living cell, but it is also considered as non living when present outside living organisms.
  • They can cause many diseases. Like, AIDS is a fatal disease and caused by HIV (Human Immunodeficiency Virus).
  • They appear to be likeplants, but they do not have leaves, roots, etc.
  • They are simple non green plants and cannot make their food by photosynthesis.
  • They are heterotrophic in nature, which means they depend on other animals for their nutritional requirement.
  • They are usually parasites, which means that they live either inside or on the body of another organism and eat their food.
  • They may be unicellular, which means that they have single cell.
  • Examples of Viruses are: Poliovirus and Tobacco mosaic virus (Tobacco mosaic is a disease in plant).

fungi

  • They appear to be plants, but they do not have leaves, roots, etc. Like mushroom is an edible fruit and does not have leaves or roots.
  • They are simple non green plants.
  • They are heterotrophic, which means they are dependant on another animal for their food.
  • Usually they are parasites.
  • They may be unicellular.

aspergillus

  • They are mostly found in aquatic bodies.
  • They are solitary or colonial, which means that they can either exist alone or live in colonies.
  • They can be free living or parasitic, which means that they can live alone or are also present inside the body of other organisms.
  • Their body shape may be irregular, oval, spherical, etc.
  • For example: Amoeba, Paramecium.

Algae is a simple, non-flowering, and typically aquatic plant of a large assemblage that includes seaweeds and many single-celled forms. Algae is green in color and also contains chlorophyll but lacks true stems, roots, leaves, and vascular tissue. Examples of Algae: Chlamydomonas, Spirogyra.

Useful Microorganisms

Useful bacteria.

  • Most bacteria act as decomposers (which means that they feed on dead and decaying organic matter) and release nutrients into soil, air etc.
  • Nitrogen fixing bacteria help in nitrogen fixation that helps in maintaining fertility of soil. Like leguminous plants, roots of these plants have nodules that contains rhizobium and that bacteria has power to fix nitrogen. Thus, it helps in maintain the fertility of soil.
  • Bacteria help in treating sewage and producing biogas from waste.
  • Many herbivores have cellulose digesting bacteria in their stomach.

vinegar

  • Some bacterias are helpful in the manufacturing of products like vinegar, ethanol, etc.
  • Bacterias are used in tanning of leather, etc.
  • Some bacteria are used in research tools, etc.

bacteria

  • They are used in baking industry for making breads, pastries, cakes etc. Yeast is used as a raising agent in baking. Most commonly used yeast is Saccharomyces cerevisiae. It is in to the action of yeast that the dough rises, if we leave it for sometime adding yeast to it during kneading.

Question: Name the microorganisms which can fix nitrogen in the soil ?

Answer: Nitrogen is needed by the plants for their growth. They cannot absorb nitrogen directly from the air. There are microorganisms like some bacteria and blue green algae in the soil that take nitrogen from the air and make nitrogenous compounds. Thus, they enrich the soil with nitrogenous compounds and make it fertile. These bacteria and blue green algae are called biological nitrogen fixer nitrogenous compounds and make it fertile. These bacteria and blue green algae are called biological nitrogen fixers.

antibiotics

Answer: Antibiotics are the medicines (drugs) that kill or stop the growth of disease causing microorganisms in our body. Thus, they help in curing the disease. They are produced from bacteria and fungi. Penicillin, Streptomycin, Tetracycline and Erythromycin are some antibiotics. While taking antibiotics following precautions must be taken –

  • Antibiotics should be taken only on the advice of a qualified doctor.
  • The course prescribed by the doctor should be finished in proper doses.
  • Antibiotics should not be taken unnecessarily as they may kill the beneficial bacteria in the body.

Question: Write a note on viruses.

Answer: Viruses are microorganisms and they do not have a cellular structure. They reproduce only inside the cells of other organisms. Viruses cause many diseases like common cold, flu, polio and chicken pox. Antibiotics do not kill viruses.

Question: What is vaccination? How does it help in protecting children from diseases?

Answer: The process of introducing weakened disease causing microorganisms in the body is called vaccination. The body kills the weakened microorganisms by producing antibodies. These antibodies remain in the body and kill the microorganisms if they enter again. In this way vaccination helps in protecting the children from diseases.

Useful Fungi

  • They act as decomposers that help in adding nutrients to soil.

decomposers

  • Yeast is also used in making alcoholic beverages and bread, idli, etc. Yeast is commonly called as ‘khameer’. Idli/ dosa batter contain urad pulses. These urad seeds contain Lactic Acid Bacteria (LAB) and this bacteria lead to the formation of Lactic acid and Carbon dioxide. Formation of Lactic acid gives a sour taste to the batter. Therefore, the batter should not be fermented for too long, else it might turn too sour.
  • Mushrooms are edible fungi.
  • Some of them are also used in research work.

Useful Algae

  • Algae is green in color and can make food by the process of photosynthesis. Thus, it helps in supplying food to aquatic animals and also produces oxygen gas that can be used for respiration.
  • Red algae is edible in certain countries.
  • Algae is used in making Toothpaste, jelly etc.
  • Some algae enrich the soil with nitrogen like blue green algae.
  • Some algae are sources of iodine and potash like brown algae.

Harmful Microorganisms

Microorganisms are harmful as they cause many diseases. There are many microbes which cause several diseases in plants, animals & human beings. Such disease-causing organisms are called Pathogens. We can also say that pathogens are diseases causing microorganisms. Pathogens include bacteria, viruses, fungi & protozoa.

Types of diseases

There are two types of diseases which are written as below:

  • Communicable
  • Non Communicable

Communicable Disease

The diseases that can spread through sick to healthy person are called communicable diseases. We can also say that the communicable diseases are those diseases which can be transferred from one person to another person. For example: Flu, cold, AIDS.

Non Communicable Disease

The diseases that do not spread through sick to healthy person are called non – communicable diseases. We can also say that the communicable diseases are those diseases which cannot be transferred from one person to another person. For example: Lung Cancer or liver damage.

Disease

Question: How do pathogens enter our body?

Answer: Pathogens enter our body through the air while breathing or through water that we drink or through the food that we eat or by direct contact with an infected person or may be carried through any carrier (any source that contains pathogens).

Question: How do pathogens cause diseases?

Answer: Pathogens enter our body through any source and multiply inside the body cell and can result in disease. For example: When any person suffering from cold sneezes, some of the droplets of moisture carrying many viruses are spread in air. The same air is inhaled by another person sitting close by or in front of the infected person. So there is a chance that virus can transmit to his body and cause infection. To prevent ourselves from this kind of infection, we need to use a handkerchief and keep it on the nose and mouth while the infected person is coughing and sneezing.

Question: What are carriers and how do they spread diseases?

Answer: Carriers are the organisms that carry the pathogens to the healthy person. For example: Malaria is caused by protozoa plasmodium (causative agent) which is transmitted to healthy person by biting of female anopheles mosquitoes. Plasmodium is present in the saliva of female mosquito. Then these pathogens splits in our body and cause various diseases.

Example of other carriers: Aedes mosquito is a carrier of dengue.

Rabied dog is a carrier of rabies. The person who has hydrophobia often suffers from rabies.

To prevent mosquitoes from entering our surroundings, we need to keep our surrounding cleans and we should not let the water collect anywhere. As mosquitoes breed in water and if they will not find water they will be unable to breed.

Common human diseases caused by microorganisms (Harmful Microorganisms)

Measles

It is caused by Virus

Air

Polio

It is caused by Virus

Air/Water

We should receive vaccination

Common plant diseases Caused by microorganisms (Harmful Microorganisms)

Now the question arises, how to Avoid Spreading of Microorganisms?

hands

  • We should wash our hands before eating, after preparing food and after using toilet.
  • We should cover our mouth while coughing or sneezing.
  • We Keep away from other people that are suffering from any disease.
  • We should not eat food which is not fresh or not cooked properly.

Question: What are the conditions that promote growth of  microorganisms?

Answer: The following conditions promote the growth of microorganisms-

  • Food having high moisture content and prone to microorganisms.
  • Food kept for long time at room temperature.
  • When skin of fruit and vegetables is damaged. This damaged skin is more prone to microorganisms or can even spoil it.
  • The food with low salt content, low sugar or acid content is more prone to microorganism.

Food preservation

Methods of preserving food at home.

The following are the methods of preserving food at home-

Dehydration

  • Freezing    

Increasing temperature

  • Using preservatives

Dehydration means removing water or moisture from food.

This stops microorganisms from growing as they cannot grow without water. It can be called sun drying. For example: Ginger, Potato chips, Fenugreek (Methi) are dehydrated and stored in houses.

Lowering temperature

We can also keep the microorganisms away from food by using low temperature. Low temperature slows down the activity of microorganisms.

For this, we make use of refrigerators for preserving food items. Food can be kept in refrigerator at about 5˚C which delays its spoilage. For e xample: Cooked Dal can be preserved by this method.

Milk

It involves two methods:

Pasteurization

Sterilization.

It is a process of heating food item to high temperature and then quickly cooling it. As microorganism cannot withstand change in temperature therefore, they get destroyed. This is a process in which milk is heated to about 70 degree Celsius for about 15 to 30 seconds and then suddenly chilled and stored. This process was discovered by Louis Pasteur.

In this process food items are exposed to high temperature for longer period of time. In some cases high pressure also used to destroy micro -organisms.

Like if we take water and boils at very high temperature it cannot withstand with that high temperature and may lead to destruction of microorganism. Or we can say that water is microorganism free.

Using Preservatives

Preservative is any substance that is added to food to keep it for long time. For example: Salt, Sugar, Acid, lemon.

Natural Preservatives

  • Sugar                       
  • Lemon juice

Chemical preservation

  • Potassium meta-bisulphate
  • Citric acid
  • Sodium Benzoate

Time to check your knowledge by answering the following questions-

Choose the correct answer from the given options-

1. What is spyrogyra ?

I. An algae

II. A fungi

III. A protozoa

IV. A bacteria

2. Who discovered the vaccine for small pox ?

I. Louis Pasteur

II. Alexander Fleming

III. Edward Jenner

IV. John Mendal

3. What is the amount of nitrogen in the atmosphere?

4. Mushroom is a

IV. None of these

5. Amoeba is a

III. Protozoa

6. What is the name of scientist who discovered fermentation?

I. Alexander Fleming

II. Louis Pasteur

III. John Mendal

IV. Edward Jenner

7. What is the use of rhizobium bacteria?

I. Help in digestion

II. Help in nitrogen fixation

III. Cause diseases

IV. All of the above

8. What is the causative agent of malaria ?

I. Protozoa

IV. Bacteria

9. Penicillium is a

III. Bacteria

10. Microorganisms are

I. Unicellular

II. Multi-cellular

      1)     II

      2)     III

      3)     III

      4)     III

      5)     III

      6)     II

      7)     II

      8)     I

      9)     II

      10)  II

Question: Explain the role of mosquitoes in spreading diseases. How can we control them? 

Answer: Mosquitoes act as carriers of many disease causing microorganisms. Anopheles mosquito carries the parasite of malaria. Female Aedes mosquito carries the dengue virus from an infected person to a healthy person. The spread of diseases can be controlled by killing the mosquitoes. The breeding places of mosquitoes like water in the coolers, tyres, flowerpots, etc. should be drained out. Mosquito nets should be used at night.

Question: What is food poisoning? What is its effect?  Answer: Microorganisms like bacteria and fungi grow in the food and produce poisonous (toxic) substances in the food. This is called food poisoning. If such food is eaten, it may cause serious illness or even death.

Question: How is food preserved from the attack of microorganisms?

Answer: Food is preserved from the attack of microorganisms by the following methods: 1. Chemical Method: Food preservatives like Sodium Benzoate are added to pickles, jams and squashes to prevent the growth of microorganisms.

2. Preservation by Common Salt: Meat and fish are preserved by covering with dry salt. Salting is also used to preserve amla, raw mangoes and pickles.

3. Preservation by Sugar: Jams, Jellies and squashes are preserved by sugar. Sweet pickles like murabba are also preserved by using sugar. Sugar prevents the growth of microorganisms.

4. Preservation by Oil and Vinegar : Oil and vinegar are used to prevent growth of microorganisms in pickles. Mustard oil is popularly used for the preservation of pickles.

5. Heat and Cold Treatment: Milk is boiled to kill the bacteria. After it cools down it is stored in a refrigerator. Low temperature also slows down the growth of bacteria.

Question: What is fermentation? How is it useful?

Answer: The process of production of alcohol from sugar by use of yeast is called fermentation. It is useful in production of wine, baking of bread, making idlis and dosas.

Question:   Write ten lines on the usefulness of microorganisms in our lives? Answer: Microorganisms are so small that we cannot see them with the naked eye. Still they are very useful for us.

1. Lactobacillus is used to form curd from milk.

2. Rhizobium bacteria present in the roots of pulse plants fixes nitrogen from the air and supplies nitrogen compounds to the pulse plants.

3. The antibiotic Penicillin is prepared from the fungus Penicillium. This antibiotic is used to cure many diseases.

4. Some bacteria and blue green algae in the soil take nitrogen from the air and make nitrogenous compounds. Thus, they make the soil fertile.

5. Bacteria present in the soil decompose the organic matter and release the nutrients in the soil making it fertile. These nutrients are absorbed by plants.

6. Yeast is used for the production of alcohol and wine.

7. Yeast is also used for making bread, pastries and cakes.

8. Yeast is also used in making of idlis and bhaturas.

9. Bacteria present in our intestines help in proper digestion and release vitamin B. This vitamin is absorbed by our intestine.

10. Many vaccines are prepared from microorganisms. These vaccines are given to children to protect them from diseases like tuberculosis, polio.

Question: Write a short paragraph on the harms caused by microorganisms.

Answer: Microorganisms are harmful in the following ways :

  • Microorganisms cause diseases like typhoid, cholera and tuberculosis in human beings.
  • Microorganisms also cause plant diseases like rust of wheat and citrus canker.
  • Microorganisms like bacteria and fungi cause food poisoning by producing toxic substances in the food.
  • Microorganisms like bacteria and fungi cause spoilage of the food, paper, leather goods and clothes.
  • Microorganisms like bacteria and protozoa cause pollution of water and make it unfit for drinking.

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grade-8-microorganisms-friend-and-foe-worksheets

Grade 8 Microorganisms: Friend and Foe Worksheets

A. Fill in the blanks:

1. Microorganisms can be seen with the help of a ………………. . 2. Blue green algae fix ……………. directly from air to enhance fertility of soil. 3. Alcohol is produced with the help of ………………… . 4. Cholera is caused by ……………….. . 5. The female Aedes mosquito is a carrier of the ……………….. virus.

B. Tick (✓) the correct option:

1. Yeast is used in the production of: (a) sugar (b) alcohol (c) hydrochloric acid (d) oxygen

2. The following is an antibiotic: (a) Sodium bicarbonate (b) Streptomycin (c) Alcohol (d) Yeast

3. Carrier of malaria-causing protozoan is: (a) female Anopheles mosquito (b) cockroach (c) housefly (d) butterfly

4. The most common carrier of Communicable diseases is: (a) ant (b) housefly (c) dragonfly (d) spider

5. The bread of idli dough rises because of: (a) heat (b) grinding (c) growth of yeast cells (d) kneading

6. The process of conversion of sugar into alcohol is called: (a) nitrogen fixation (b) moulding (c) fermentation (d) infection

C. Match the following:

‘A’ ‘B’
1. Bacteria a. Fixing nitrogen
2. Rhizobium b. Setting of curd
3. Lactobacillus c. Baking of brea
4. Yeast d. Causing malaria
5. A protozoan f. Causing cholera
6. A virus g. Causing AIDS
h. Producing antibodies

D. Answer the following questions in short:

1. Can microorganisms be seen with the naked eye? If not, how can they be seen? 2. What are the major groups of microorganisms? 3. Name the microorganisms which can fix atmospheric nitrogen in the soil. 4. Write 10 lines on the usefulness of microorganisms in our lives. 5. Write a short paragraph on the harms caused by microorganisms. 6. What are antibiotics? What precautions must be taken while taking, antibiotics? 7. What is food preservation? 8. Is it safe to eat infected bread? Why? 9. Why do foods like dry soup mixes remain unspoilt for many days?

E. State True or False:

1. Bacteria possess characteristics of living as well as non-living. ……………….. 2. Yeast is used in the preparation of vitamin ‘B’ complex. ………………. 3. All viruses are parasites. ………………… 4. All algae can make their own food because they contain chlorophyll. ……………….. 5. Microorganism may be unicellular or multicellular. ……………..

F. Classify the following into friendly and harmful microorganisms:

  • malarial parasite
  • Lactobacillus
  • bread mould
  • Bacillus anthracis
Friendly harmful

G. Visit a doctor. Find out why antibiotics should not be overused. Prepare a short report.

H. Here is a list of food items. Tick (✓) the food items you think are prone to spoilage from microorganisms:

  • Uncooked rice
  • Cooked rice

I. Complete the following cycle given as figure by filling the blank boxes:

CBSE Class 8 Science Microorganisms Friend and Foe Worksheets 1

Worksheets for Class 8 Science

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assignment of microorganisms class 8

Microorganisms: Friend And Foe Class 8 Science Extra Questions and Answers

Microorganisms Friend and Foe Class 8 Science Chapter 2 Extra Questions and Answers are provided here. We prepared these extra questions based on the latest NCERT Class 8 Science Book. CBSE Class 8 Science Chapter 2 Microorganisms: Friend and Foe Extra Questions will help you to properly understand a particular concept of the chapter.

Class 8 Science Chapter 2 Microorganisms: Friend and Foe Extra Questions

Very short answer type questions.

Question 1: What causes malaria?

Answer: Malaria is caused by protozoa.

Question 2: Which mosquito act as carrier of dengue virus?

Answer: Aedes mosquito acts as carrier of dengue virus.

Question 3: Name any two diseases that can be prevented by vaccination.

Answer: Polio and smallpox

Question 4: Give two examples of algae.

Answer: Chlamydomonas and Spirogyra

Question 5: Give two examples of protozoa.

Answer: Amoeba and Paramecium

Question 6: How are cholera and typhoid caused?

Answer: Cholera and typhoid are caused by bacteria.

Question 7: Give few of examples of fungi.

Answer: Bread mould, Penicillium and Aspergillus

Question 8: Who discovered penicillin?

Answer: In 1929, Alexander Fleming discovered penicillin.

Question 9: Name any two diseases caused by bacteria.

Answer: Typhoid and tuberculosis (TB)

Question 10: What causes foot and mouth disease of cattle?

Answer: Foot and mouth disease of cattle is caused by a virus.

Question 11: Who discovered the vaccine for smallpox?

Answer: Edward Jenner discovered the vaccine for smallpox in 1798.

Question 12: Name any two diseases caused by protozoa.

Answer: Diseases like dysentery and malaria are caused by protozoans.

Question 13: Name some antibiotics.

Answer: Streptomycin, tetracycline and erythromycin

Question 14: How are meat and fish preserved?

Answer: Meat and fish are covered with dry salt to check the growth of bacteria.

Question 15: What is fermentation?

Answer: The process of conversion of sugar into alcohol is called fermentation.

Question 16: Why do we boil milk before storing?

Answer: We boil milk before storing because boiling kills many microorganisms.

  Question 17: Name one plant disease caused by bacteria and its mode of transmission.

Answer: Citrus canker is caused by bacteria and transmitted through air.

Question 18: Why are the antibiotics not effective against colds and the flu?

Answer: Antibiotics are not effective against cold and flu as these are caused by viruses.

Question 19: Name one plant disease caused by virus and its mode of transmission.

Answer: Yellow vein mosaic of bhindi (Okra) is caused by virus and transmitted through insect.

Question 20: How can we control plant diseases?

Answer: They can be controlled by the use of certain chemicals which kill the microbes.

Question 21: Name one plant disease caused by fungi and its mode of transmission.

Answer: Rust of wheat is caused by fungi and transmitted through air and seeds.

Question 22: What causes food poisoning?

Answer: Food poisoning could be due to the consumption of food spoilt by some microorganisms.

Question 26: How do we preserve pickles?

Answer: We add salt or acid preservatives to pickles to prevent the attack of microbes.

Question 27: What are preservatives?

Answer: Chemicals (Salts, edible oils etc.) used to check the growths of microorganisms are called preservatives.

Question 28: Why pasteurized milk can be consumed without boiling?

Answer: Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Short Answer Type Question

Question 1: Name some unicellular and multicellular organisms.

Answer: Unicellular organisms- bacteria, some algae and protozoa

Multicellular organisms- algae and fungi

Question 2: How can we prevent the spread of communicable diseases?

Answer: We prevent the spread of communicable diseases:

  • By keeping handkerchief on the nose and mouth while sneezing.
  • By keeping distance from infected persons.

Question 3: How are viruses different from other microorganisms?

Answer: Viruses are quite different from other microorganisms. They reproduce only inside the host organism; bacterium, plant or animal cell.

Question 4: How do microorganisms clean the environment?

Answer: Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.

Question 5: How are jams and squashes preserved?

Answer: Sodium benzoate and sodium metabisulphite are used in the jams and squashes to check their spoilage.

Question 6: What are the major groups of microorganisms?

Answer: Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.

Question 7: What are microorganisms?

Answer: Microorganisms or microbes are the living organisms around us which cannot be seen with naked eye.

Question 8: What diseases are prevented through vaccination?

Answer: Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

Question 9: Why do we keep food in refrigerator?

Answer: We keep food in the refrigerator because low temperature inhibits the growth of microbes and keep the food fresh.

Question 10: Why dry fruits and even vegetables are sold in sealed air tight packets?

Answer: Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Question 11: Why is it important to vaccinate small children?

Answer: It is important to vaccinate small children in order to protect them against several diseases.

Question 12: Who discovered the bacterium which causes anthrax disease?

Answer: Robert Köch (1876) discovered the bacterium (Bacillus anthracis) which causes anthrax disease.

Question 13: How are cholera and typhoid transmitted?

Answer: Cholera is transmitted through water or food. Typhoid is transmitted through water.

Question 14: Write any two common cattle diseases and its cause.

Answer: Anthrax is a dangerous cattle disease caused by a bacterium.

Foot and mouth disease of cattle is caused by a virus.

Question 15: Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.

Question 16: Why sugar is used as preservative?

Answer: Sugar is used as preservative in jams, jellies and squashes. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.

Question 17: Which microorganism is used for commercial production of alcohol, wine and acetic acid (vinegar)?

Answer: Yeast is used for commercial production of alcohol, wine and acetic acid (vinegar).

Question 18: Name some commonly known antibiotics which are made from fungi and bacteria.

Answer: Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

Question 19: What are the harmful effects of microorganisms on plants?

Answer: Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops.

Question 20: Name some diseases caused by virus.

Answer: Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses.

Question 21: How does food become poisonous?

Answer: Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Question 22: How can we prevent the spread of hepatitis B?

Answer: Ways to prevent the spread of hepatitis B

  • Drink boiled drinking water.
  • Vaccination

Question 23: Name the bacterium found in the roots of pea plant. How is this bacterium useful?

Answer: Rhizobium lives in the root nodules of leguminous plants such as beans and peas. It is involved in the fixation of nitrogen in leguminous plants (pulses).

Question 24: Why should we keep our food covered?

Answer: Flies sit on uncovered food and they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. So, it is advisable to always keep food covered.

Question 25: Why are viruses considered to be on the borderline between living organisms and non-living things?

Answer: Viruses are also microscopic. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

Question 26:   Write some common uses of yeast.

Answer: Common uses of yeast are:

  • It is used in the baking industry for making breads, pastries and cakes.
  • It is used for commercial production of alcohol and wine.

Long Answer Type Question

Question 1: How can food be preserved by adding oil and vinegar?

Answer: Use of oil and vinegar prevents spoilage of food because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

Question 2:  How milk is turned into curd?

Answer: A little curd is added to warm milk to set curd. Curd contains several microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.

Question 3: How does common cold spread?

Answer: When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing.

Question 4: Why is tuberculosis considered as infectious disease?

Answer: Tuberculosis is considered as infectious disease because bacteria that cause tuberculosis are spread from one person to another through tiny droplets released into the air via coughs and sneezes.

Question 5: What causes tuberculosis and how is it spread?

Answer: Tuberculosis is caused by bacteria that spread from person to person through microscopic droplets released into the air. This can happen when someone with tuberculosis coughs, speaks, sneezes or spits.

Question 6: What are biological nitrogen fixers?

Answer: Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Question 7: How can cholera be prevented?

Answer: To prevent cholera we must:

  • Maintain personal hygiene and good sanitary habits.
  • Consume properly cooked food and boiled drinking water.
  • Vaccination.

Question 8: What are pathogens?

Answer: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens.

Question 9: How do pathogens enter our body?

Answer: Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal.

Question 10:  Why should we not let water collect anywhere in the neighbourhood?

Answer: All mosquitoes breed in water. Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc. By keeping the surroundings clean and dry we can prevent mosquitoes from breeding.

Question 11: What will happen if we take antibiotics when not needed?

Answer: If we take antibiotics when not needed or in wrong doses, it may make the drug less effective when we might need it in future.Also antibiotics taken unnecessarily may kill the beneficial bacteria in the body.

Question 12: What are carriers of disease-causing microbes? Give examples.

Answer: There are some insects and animals which act as carriers of disease-causing microbes. Housefly is one such carrier. Another example of a carrier is the female

Anopheles mosquito, which carries the parasite of malaria.

Question 13: What happens when yeast powder is added to sugar solution and kept for 4-5 hours?

Answer: When yeast powder is added to sugar solution and kept for 4-5 hours, fermentation takes place. Sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.

  Question 14: Why is yeast used in baking industry?

Answer: Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

Question 15: How do houseflies spread disease?

Answer: Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick.

Question 16: Write a short paragraph on the harms caused by microorganisms.

Answer: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.

Question 17: What is called pasteurization?

Answer: It is a process in which milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Question 18: What are communicable diseases? Give examples.

Answer: Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

Question 19: Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: Microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Question 20: Where do microorganisms live?

Answer: They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.

Question 21:  Why is curd an important ingredient in making rava idlis and bhaturas?

Answer: Curd is added while making idli and bhatura dough as curd contains Lactobacillus bacteria that undergoes anaerobic respiration and in this process it acts on sugar of the flour and releases carbon dioxide gas, this gas make the dough rise and when baked or fried gas escapes leaving the idli or bhatura soft and spongy.

Question 22:  How a vaccine works?

Answer: When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes. This is how a vaccine works.

Question 23:  Mention some important uses of fungi.

Answer: Uses of fungi are as follows:

  • Some antibiotics are made from fungi.
  • When plants and animals die fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.
  • Yeasts are single-celled fungi. It is used in baking industry for making breads, pastries and cakes and for commercial production of alcohol and wine.

Question 24: Write 10 lines on the usefulness of microorganisms in our lives.

Answer: Microorganisms play an important role in our lives. Some of them are beneficial in many ways.

  • They are used in the preparation of curd, bread and cake.
  • They are used for the large-scale production of alcohol, wine and acetic acid (vinegar).                        
  • They are also used in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals etc.) are broken down into harmless and usable substances by bacteria.
  • Bacteria are also used in the preparation of medicines.
  • In agriculture they are used to increase soil fertility by fixing nitrogen.

Question 25:  What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: Antibiotics are the medicines prepared from microorganisms to kill or stop the growth of the disease-causing microorganisms.

Precautions to be taken while taking antibiotics:

  • Antibiotics should be taken only on the advice of a qualified doctor.
  • Course of antibiotics should be completed as prescribed by the doctor.
  • Antibiotics should be taken in the right amount and at the right time. If antibiotics are taken unnecessarily it may kill the beneficial bacteria in the body.
  • Antibiotics are not effective against cold and flu as these are caused by viruses.

Question 26: Explain nitrogen cycle.

Answer: Our atmosphere has 78% nitrogen gas. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

Question 27:  What are the different methods of food preservation?

Answer: Different methods of food preservation are:

  • Chemical Method – Salts and edible oils are the common chemicals generally used to check the growth of microorganisms.
  • Preservation by Common Salt – Common salt has been used to preserve meat and fish for ages. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
  • Preservation by Sugar – Jams, jellies and squashes are preserved by sugar.
  • Preservation by Oil and Vinegar – Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
  • Heat and Cold Treatments – This process kills many microorganisms. Milk is boiled before it is stored or used.
  • Storage and Packing – Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.
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  • Chapter 2: Microorganisms Friend And Foe

NCERT Exemplar Class 8 Science Solutions for Chapter 2 - Microorganisms Friend and Foe

Ncert exemplar solutions class 8 science chapter 2 – free pdf download.

NCERT Exemplar Solutions for Class 8 Science Chapter 2 Microorganisms: Friend and Foe will assist students in cross-checking their knowledge on various concepts and topics in Microorganisms. Students who are planning to take the annual exam should study this NCERT Exemplar Solutions Class 8 Science thoroughly to understand the concepts from the exam point of view.

The NCERT Exemplar has answers to the questions provided in the NCERT Exemplar book. All the questions provided in exemplar books are solved by the subject experts, and this page has answers to 7 MCQs, 9 very short answer questions, and 11 short answer questions. The chapter Microorganisms: Friend and Foe are about learning what microorganisms are and how they help us to survive. In this chapter, students will learn about different types of microorganisms, like friendly microorganisms and harmful microorganisms. Visit the below link to get a free downloadable PDF.

NCERT Exemplar Class 8 Science Solutions for Chapter 2 – Microorganisms Friend and Foe

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Access Answers to NCERT Exemplar Class 8 Science Chapter 2 – Microorganisms Friend and Foe

Multiple-choice questions.

1. Which of the following reproduces only inside a host cell?

(a) Bacteria

(d) Fungus.

The answer is (b) Virus

Explanation:

The virus is considered as an intermediate between living and non-living. Outside, a host-virus remains inactive. It can perform its life processes and reproduction only when it is inside a host cell.

2. A disease in human beings caused by a virus is _______.

(a) Typhoid

(b) Influenza

(c) Dysentery

(d) Cholera

The answer is (b) Influenza

Typhoid is caused by bacteria Salmonella typhoid.

Dysentery is caused by an amoeba which is a protozoan.

Cholera is caused by Vibrio cholera bacteria.

3. Pathogenic micro-organisms present in host cells are killed by medicines called

(a) Pain killer

(b) Antibodies

(c) Antibiotics

(d) Vaccines

The answer is (b) Antibiotics

  • Pain Killers gives relief from pain.
  • Antibodies are produced by our immune system which acts and elicit a specific immune reaction.
  • Antibiotics that inhibit or kill certain bacteria.
  • Vaccines provide acquired immunity against a particular disease.

4. The two micro-organisms which live in symbiotic association in lichens are

(a) Fungus and Protozoa

(b) Alga and Bacteria

(c) Bacteria and Protozoa

(d) Alga and Fungus

The answer is (d) Alga and Fungus

5. The gas released during the preparation of bread is

(b) Carbon dioxide

(c) Nitrogen

(d) Sulphur dioxide

The answer is (b) Carbon dioxide

Carbon-di-oxide is released due to the fermentation process conducted by yeast. CO 2 causes rising of the dough and makes the bread fluffy.

6. The disease caused by a protozoan and spread by an insect is _________.

(b) Malaria

(d) Measles

The answer is (b) Malaria

Malaria is caused by protozoan named Plasmodium vivax which is transmitted by mosquitos. Other options are viral diseases hence they are wrong answers.

7. Paheli dug two pits, A and B, in her garden. In-pit A, she put a polythene bag packed with some agricultural waste. In-pit B, she dumped the same kind of a waste but without packing it in a polythene bag. She then covered both the pits with soil. What did she observe after a month?

(a) Waste in pit A degraded faster than that in pit B.

(b) Waste in pit B degraded faster than that in pit A.

c) Waste in both pits degraded almost equally.

(d) Waste in both pits did not degrade at all.

The answer is (b) Waste in pit B degraded faster than that in pit A.

Waste in pit B degrades faster than waste in pit A because Polythene in pit B is open and receives oxygen for composting whereas polythene in closed in pit A and organisms don’t receive oxygen to compost the waste material in the polythene bag.

Very Short Answer Questions

8. Unscramble the jumbled words underlined in the following statements.

(a) Cells of our body produce santiidobe to fight pathogens.

(b) curbossulite is an air-borne disease caused by a bacterium.

(c) Xanrhat is a dangerous bacterial disease.

(d) Yeasts are used in the wine industry because of their property of meronettinaf.

a. Antibodies

b. Tuberculosis

d. Fermentation

9. Suggest a suitable word for each of the following statements.

(a) Chemicals added to food to prevent the growth of microorganisms.

(b) Nitrogen-fixing microorganism present in the root nodules of legumes.

(c) The agent spreads pathogens from one place to another.

(d) Chemicals which kill or stop the growth of pathogens.

a. Preservatives

b. Rhizobium

c. Carrier/ vector

d. Antibiotics

10. Match the names of scientists given in Column A with the discovery made by them given in Column B.

Column A – Column B

(a) Louis Pasteur – (i) Penicillin

(b) Robert Koch – (ii) anthrax bacterium

(c) Edward Jenner – (iii) Fermentation

(d) Alexander Fleming – (iv) smallpox vaccine

(a) Louis Pasteur – (iii) Fermentation

(c) Edward Jenner – (iv) smallpox vaccine

(d) Alexander Fleming – (i) Penicillin

11. Name one commercial use of yeast

Yeast is used in making bread and they are used in the fermentation of alcohol.

12. Name the process in yeast that converts sugars into alcohol.

Fermentation is the process in yeast that converts sugars into alcohol.

13. In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?

Blue-green-algae enriches Nitrogen in the soil.

14. Why should we avoid standing close to a tuberculosis patient while he/she is coughing?

Tuberculosis can spread through the air when the infected person coughs. Hence we avoid standing close to a tuberculosis patient while he/she is coughing.

15. Polio drops are not given to children suffering from diarrhoea. Why?

If the children are suffering from diarrhoea oral polio drops will get excreted due to frequent motions. Hence children with diarrhoea are not given with polio drops.

16. Paheli watched her grandmother making mango pickle. After she bottled the pickle, her grandmother poured oil on top of the pickle before closing the lid. Paheli wanted to know why oil was poured? Can you help her understand why?

Oils prevent the attack of bacteria which will help preserve the pickle for a long period of time.

Short Answer Questions

17. Match the microorganisms given in Column A to the group to which they belong in Column B.

(a) Lactobacillus – (i) Algae

(b) Aspergillus – (ii) Protozoa

(c) Spirogyra – (iii) Fungi

(d) Paramecium – (iv) Bacteria

(a) Lactobacillus – (iv) Bacteria

(b) Aspergillus – (iii) Fungi

(c) Spirogyra – (i) Algae

(d) Paramecium – (ii) Protozoa

18. Classify the following into friendly and harmful microorganisms.

Yeast, malarial parasite, Lactobacillus , bread mould, Rhizobium , Bacillus anthracis

Yeast Malarial parasite
Bread mould

19. While returning from the school, Boojho ate chaat from a street hawker. When he reached home, he felt ill and complained of stomach ache and fell ill. What could be the reason?

The probable reason is that the chaat was contaminated by pathogenic microbes due to unhygienic conditions near the shop, or the utensil used for serving could have been contaminated.

The reason may be the contamination of food by pathogenic microbes. Contamination may be due to the unhygienic conditions near the shop or the utensil used to serve the chaat.

20. What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left in the open for a day or two?

Pooris and unused kneaded flour get spoiled due to microbial activity. Food gets fermented when kept open and it will be spoiled.

21. (a) Name two diseases that are caused by the virus.

(b) Write one important characteristic of the virus.

a. Polio, HIV

b. A virus can reproduce only when it is inside the host cell.

Long Answer Questions

22. Observe the Fig.2.1 and answer the questions that follow.

NCERT Exemplar Class 8 Science chapter 2 Solutions fig 1

(a) Write the name of the disease.

(b) Name the causative agent of this disease?

(c) How does the disease spread from one plant to another?

(d) Name any two plant diseases and the microbes that cause them.

a. Yellow vein mosaic of lady’s finger/okra

b. This disease is caused by a virus called Yellow vein mosaic virus.

c. This disease spread from one plant to another by insects.

d. (i) Citrus canker caused by bacteria (ii) Rust of wheat caused by the fungus

23. How do vaccines work?

When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes forever. This is how a vaccine works.

24. Observe the set up given in Fig. 2.2 and answer the following questions.

(a) What happens to the sugar solution in A?

(b) Which gas is released in A?

(c) What changes will you observe in B when the released gas passes through it?

NCERT Exemplar Class 8 Science chapter 2 Solutions fig 2

a) Yeast ferments sugar to convert it to alcohol and carbon-di-oxide is released.

b) Carbon-di-oxide

c) CO 2 Coverts limewater milky. 25. Observe the Fig.2.3 and answer the following questions.

NCERT Exemplar Class 8 Science chapter 2 Solutions fig 3

(a) Name the microorganism and the group to which it belongs.

(b) Name the food item on which the organism grows.

(c) Does it grow well in dry or in moist conditions?

(d) Is it safe to eat infected bread?

a) The image is of bread mould. It is a fungus

b) It grows on moist and stale bread

c) It grows well in moist conditions

d) No, it is not safe to eat infected bread because fungus produces a poisonous substance which will spoil the food.

26. Give reasons for the following.

(a) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed without boiling.

(b) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside.

(c) Farmers prefer to grow beans and peas in nitrogen-deficient soils.

(d) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?

a) Fresh milk is boiled to kill the harmful microorganisms in the milk. Packed milk is pasteurized hence there is no need to boil the pasteurized milk.

b)Raw vegetables easily get infected by microbes. Hence they are kept in the refrigerator as low temperature inhibits the growth of micro-organisms. In Jams and pickle, there are sugar and salt which acts as preservatives. Hence they do not get infected easily.

c) Beans and peas are leguminous plants which have Rhizobium in their root nodules. Rhizobium fixes atmospheric Nitrogen to enrich the soil and its fertility gets increases.

d) Though mosquitos do not live in water. But they lay their egg and their larvae grow in water. Hence mosquitoes can be controlled by preventing stagnation of water.

27. How can we prevent the following diseases?

(a) Cholera

(b) Typhoid

(c) Hepatitis A

a) Cholera can be prevented by following good personal hygiene and sanitation practices.

b) Typhoid can be prevented by eating properly cooked food, by drinking boiled water and by getting vaccinated against typhoid disease.

c) Hepatitis can be prevented by drinking boiled water and by getting vaccinated.

28. Complete the following cycle given as Fig. 2.4 by filling the blanks (a), (b), (c) (d)

NCERT Exemplar Class 8 Science chapter 2 Solutions fig 4

(a) Lightning fixes nitrogen.

(b) Nitrogen-fixing bacteria and blue-green algae fix atmospheric nitrogen.

(c) Nitrogenous waste from excretion and death.

(d) Bacteria turn compounds of nitrogen into gaseous nitrogen.

Topics of NCERT Exemplar for Microorganisms Friend and Foe Class 8 NCERT Solutions

  • Microorganisms
  • Habitats of Microorganisms
  • Microorganisms and us
  • Harmful microorganisms
  • Food preservation
  • Nitrogen fixation
  • Nitrogen cycle

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Microorganisms: Friend and Foe Class 8 Extra Questions Science Chapter 2

October 11, 2019 by Sastry CBSE

Microorganisms: Friend and Foe Class 8 Extra Questions Very Short Answer Questions

Question 1. Name the groups in which microorganisms are broadly classified. Answer: Microorganisms are broadly classified in four groups:

Question 2. Name the type of microorganism that is smaller than bacteria. Answer: Virus

Question 3. Write the name of a bacterium that helps in the formation of curd. Answer: Lactobacillus

Question 4. Write a use of yeast. Answer: Yeast is used in the production of alcohol, wine, beer and other beverages.

Question 5. What does yeast produce during respiration? Answer: Yeast produces carbon dioxide gas during respiration.

Question 6. What are pathogens? Write another name of pathogens. Answer: Disease-causing microorganisms are known as pathogens. They are also called germs.

Question 7. Define food preservation. Answer: Food preservation is the method of preserving food from being spoiled by the microbes.

Question 8. Write the names of any two antibiotics. Answer:

  • Streptomycin
  • Erythromycin

Question 9. Who discovered the vaccine for small pox? Answer: Edward Jenner

Question 10. What is fermentation? Answer: Fermentation is the process of conversion of food into alcohol.

Question 11. Define refrigeration. Answer: The storing of food products at the temperature of 0°C to 5°C is known as refrigeration.

Question 12. What is vaccine? Answer: A substance which is used in the production of immunity against various diseases in the living body is termed as vaccine.

Question 13. Name any two human diseases caused by viruses. Answer:

Question 14. Name any three common plant diseases. Answer: Rust of wheat, citrus canker and wilt

Question 15. Name a microorganism which helps in nitrogen fixation. Answer: Rhizobium

Question 16. Name a disease caused by food poisoning. Answer: Botulism

Question 17. What is the difference between refrigeration and freezing? Answer: In refrigeration, the storing of the food is done at a temperature of 0°C to 5°C, whereas freezing is used to store food at -18°C of temperature.

Question 18. What is decomposition? Answer: Decomposition is the process in which organic materials are broken down into simple inorganic sub-stances by the microorganisms.

Question 19. Name the two microbes that are involved in the process of decomposition. Answer: Bacteria and fungi

Question 20. Name the first antibiotic discovered. Answer: Penicillin

Microorganisms: Friend and Foe Class 8 Extra Questions Short Answer Questions

Question 1. What are microorganisms? Give four examples. Answer: Small organisms that cannot be seen through the naked eyes and can only be seen under a microscope are called microorganisms or microbes; e.g., Amoeba, Paramecium, Volvox, Spirogyra, etc.

Question 2. Classify bacteria on the basis of their shapes. Answer: On the basis of their shapes, bacteria are classified into four categories:

  • rod-shaped bacteria (bacilli)
  • spherical-shaped bacteria (cocci)
  • curved-shaped bacteria (vibrios)
  • spiral-shaped bacteria (spirilla)

Question 3. Define communicable diseases. Give some examples. Answer: Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, or other physical contacts; e.g., cholera, chicken pox, tuberculosis, common cold, etc.

Question 4. Differentiate between viruses and other microorganisms. Answer:

(i) They show the characteristics of living organ­isms or reproduce only by entering the host or­ganisms. (i) They do not need to enter any host organ­ism to reproduce or show any characteristics of life.
(ii) They are non-cellular microbes. (ii) They are cellular microbes.

Question 5. What do you mean by food spoilage? Answer: The process in which food is deteriorated to such extent that it does not remain fit for human consumption is known as food spoilage.

Question 6. What role does sugar play in the preservation of food? Answer: The role of sugar in food preservation is significant. By adding sugar in the food item, we reduce its moisture content and hence, it stops the growth of the microorganisms.

Question 7. How are carriers harmful to us? Answer: Carriers take with them many harmful microorganisms or pathogens. They play a great role in transferring these pathogens to a healthy person, by sitting on the food items, or directly transferring the pathogens inside the body of a person. Hence they are harmful to us.

Question 8. What is vaccination? Answer: The process of putting a vaccine inside the body of a person in order to produce immunity against some disease is called vaccination.

Question 9. What do you mean by immunity? Answer: Immunity is the ability of a body to develop resistance against diseases.

Question 10. Give two examples of each of the following types of microorganisms: (a) Algae (b) Fungi (c) Protozoa Answer: (a) Algae – Spirogyra, Chlamydomonas (b) Fungi – Aspergillus, yeast (c) Protozoa – Paramecium, Amoeba

Question 11. What are antibodies? Answer: Whenever any harmful disease-causing microorganism enters the human body, the body produces substances to fight with the entered microbe. These substances are called antibodies.

Question 12. What is the role of bacteria in increasing the soil fertility? Answer: Some bacteria, which are present in the root nodules of leguminous plants or free-living fix the atmospheric nitrogen in the soil which is ultimately used up by the plants. Hence they increase the fertility of the soil. For example, Rhizobium, Azotobacter, Azospirillum, etc.

Question 13. Define Ohmic heating. Answer: Ohmic heating is the process in which electric current of high voltage is passed through the food items to kill the microbes that cause the spoilage of food.

Question 14. What is sterilisation? Answer: The process of killing all the microorganisms above the temperature of 100°C is known as sterilisation. It is one of the widely used methods to preserve food, and is often used for various food items.

Question 15. What is pasteurisation? Answer: Pasteurisation can be defined as the partial sterilisation of foods at a temperature that destroys harmful microorganisms without major changes in the chemical property of the food.

Microorganisms: Friend and Foe Class 8 Extra Questions Long Answer Questions

Question 1. Explain why antibiotics do not work against flu or any infection caused by viruses. Answer: Viruses cannot be killed by using antibiotics as their cell pathways are different from that of bacteria. It means taking antibiotics to get rid of flu or any other viral infection is useless, because it does not re-duce the strength of the virus, nor does it reduce the duration of the infection. But, however, antibiotic will work if we get attacks of viral infection and bacterial disease at the same time. Even then, it will cure bacterial disease only but not the viral infection.

Question 2. Mention any three ways through which pathogens are transmitted. Answer: Three ways because of which pathogens are transmitted are as follows:

  • When a person sneezes or coughs, tiny droplets containing a number of disease-causing microorganisms come out of the mouth, and are released in the air. They are transmitted to a healthy person while breathing.
  • By making direct contacts with an infected person, pathogens are transferred to a healthy person.
  • Carriers of pathogens also help in their transmission. For instance, when a fly sits on animal excreta or garbage, harmful disease-causing microbes stick to its legs. And when this fly sits on the food items, pathogens get transferred to them. This contaminated food items cause serious diseases when it is eaten by a healthy person.

Question 3. Explain canning. Answer: Canning is a process used for food preservation. Heat, at a certain temperature and for a limited period of time, is used to kill the harmful microorganisms as well as enzymes. This method also involves the removal of oxygen gas, and to avoid post-process contamination by airtight sealing of food items.

Question 4. Explain how malaria is transmitted to humans. Answer: A protozoan called Plasmodium is responsible for malaria. It lives in the liver and blood of the person who has been infected by this disease. A female Anopheles mosquito when sucks blood from the infected person, Plasmodium along with blood, is taken into its stomach. The Plasmodium, here, multiplies itself and reaches the salivary gland of the mosquito. Now, when this mosquito bites a healthy person, it injects Plasmodium along with saliva to him. The healthy person then gets an attack of malaria. In this way, malaria is transmitted to humans.

Question 5. Explain various types of bacteria. Answer: Bacteria are classified on the basis of their shapes into the following categories:

  • Rod-shaped bacteria (bacilli): These are aerobic rod-shaped, spore-producing bacteria. They are often occurring in chain-like formations, and they are found primarily in soil; e.g., Lactobacillus.
  • Spherical-shaped bacteria (cocci): They are spherical or nearly spherical bacteria; e.g., Streptococcus.
  • Curved-shaped bacteria (vibrios): They are curved-shaped bacteria; e.g., Vibrio.
  • Spiral-shaped bacteria (spirilla): They are flagellated, aerobic bacteria, having a spirally twisted rod-like form; e.g., Treponema.

Microorganisms: Friend and Foe Class 8 Extra Questions Higher Order Thinking Skills

Question 1. Unscramble the jumbled words underlined in the following statements (a) Curbossulite is an air-borne disease caused by a bacterium. (b) Xanrhat is a dangerous bacterial disease. (c) Yeasts are used in the wine industry because of their property of meronettinaf. (d) Cells of our body produce santiidobe to fight pathogens. (e) Aeeessrrwtip are added to food to prevent growth of microorganisms. Answer: (a) Tuberculosis (b) Anthrax (c) Fermentation (d) antibodies (e) Preservatives

Question 2. What is the difference between Rhizobium and cyanobacteria in the way of fixing nitrogen for the plants? Answer: Rhizobium lives in the root nodules of leguminous plants in a symbiotic relationship whereas cyanobacteria lives freely in the soil and fixes nitrogen.

Question 3. It is always suggested that not to eat anything from street hawkers. Why? Answer: Most of street hawkers sells food items in an open area which always get contaminated with the dust and flies carrying germs with them. Such an unhygienic condition lead to spoilage of food which when consumed can lead to serious illness.

Question 4. Why oil is added while making pickle? Answer: Oil seals off the air from the item that is being pickled and thus inhibit the growth of most of the microorganisms.

Question 5. Ria thought of making curd. For this, she took lukewarm milk, mixed some curd into it and stir well. She kept the mixture in fridge. Next day she observed that curd was not set. Can you tell why the curd did not set? Answer: Curd did not set because she kept the mixture in fridge. Lower temperature of fridge retarded the growth of Lactobacillus in the mixture.

Question 6. Why do idli and dosa maker add some yeast or old batter of pervious day to the newly-made batter and keep it for one day? Answer: For fermentation of idli and dosa yeast or old batter is added. Fermentation makes idli fluffy and dosa crispy, and change the flavour.

Microorganisms: Friend and Foe Class 8 Extra Questions Value-Based Questions

Question 1. Seema got cough and cold badly. Her teacher asked her to take rest at home and use handkerchief while sneezing and coughing. She obeyed her teacher. (a) Why should we keep a handkerchief on nose and mouth while sneezing or coughing? (b) What are the modes of transfer of diseases from infected to healthy person? (c) Do you think Seema’s teacher decision was right? Why? (d) What value of Seema is shown here? Answer: (a) We should keep a handkerchief on nose and mouth while sneezing or coughing because fine drop¬lets carrying thousands of viruses or bacteria spread in the air. (b) Air, water, food, carriers and physical contact. (c) Yes, because cough and cold spreads through air and there are chances that other students may also get infected. (d) Seema is an obedient girl.

Question 2. On Rahul’s birthday, his mother prepared many dishes for him. After having their meal, they found that many food items were left over. Rahul’s mother kept these leftovers in a air-tight container and refrigerate them. (a) What is food preservation? (b) What will happen to the food if it is not refrigerated? (c) What is the role of refrigeration in food preservation method? (d) What value of Rahul’s mother is shown here? Answer: (a) The methods used for prevention of spoiling of food by the action of microbes is called food preservation. (b) The food will get spoil and emit bad smell with changed colour or taste. (c) Refrigeration retards or slow down the growth of microorganisms and enzyme activity on food. Thus, it prevents spoilage of food. (d) Rahul’s mother is intelligent, economical, have scientific aptitude towards preservation of food.

Microorganisms Friend and Foe Class 8 Extra Questions Science Chapter 2 1

Question 2. Collect the labels from the bottles of jams and jellie on the labels. Answer: Do it yourself.

Question 3. Visit a dcotor. Find out why antibiotics should not be overused. Prepare a short report. Answer: To kill or stop the development of the disease-causing microbes, antibiotics are the medicines which are majorly used. It’s very important to keep in mind that antibiotics must be taken only on the advice of a qualified doctor. Also, one should finish the prescribed course of antibiotics given by the doctor. If one takes an an¬tibiotic when not required or overuse it, then it will help bacteria in one’s body to develop resistance to the given antibiotic. Next time when one falls sick and needs that antibiotic, it will be less effective. Excess dose of antibiotics also kills friendly microbes inside our body and thus helps to flourish patho-genic microbes.

Microorganisms Friend and Foe Class 8 Extra Questions Science Chapter 2 2

I. Multiple Choice Questions (MCQs) Choose the correct option. Question 1. Tiny organisms which cannot be seen with the naked eyes are called (a) microorganisms (b) animals (c) fungi (d) bacteria

Question 2. Microorganisms are also known as (a) yeast (b) microbes (c) viruses (d) Amoeba

Question 3. Fungus can be seen with a (a) microscope (b) telescope (c) magnifying glass (d) both (a) and (c)

Question 4. Microorganisms that causes disease are also kn (a) pathogens (b) fungi (c) antigen (d) microbes

Question 5. Pathogens are also called (a) germs (b) antigen (c) antibody (d) carrier

Question 6. Bacteria are organisms. (a) multicellular (b) unicellular (c) bicellular (d) tricellular

Question 7. Bacilli are the bacteria that are (a) rod-shaped (b) comma-shaped (c) curved-shaped (d) spiral

Question 8. Spherical-shaped bacteria are called (a) bacilli (b) vibrio (c) spirilla (d) cocci

Question 9. Simple, plant-like microorganisms are called (a) algae (b) bacteria (c) both (a) and (b) (d) protozoa

Question 10. Medium that transmits pathogens from an infected person to a healthy one is called (a) fungi (b) germs (c) carrier (d) none of these

Question 11. Medicine that kills or stops the growth of harmful disease-causing microbes is known as (a) antibiotic (b) antibody (c) antigen (d) vaccine

Question 12. The process in which sugar in the food is transformed into alcohol and carbon dioxide by using microorganisms is known as (a) transformation (b) beverage (c) fermentation (d) respiration

Question 13. The fungus that is commonly used in bakery and beverage industries is (a)Penicillium (b) Yeast (c) Agaricus (d) Rhizopus

Question 14. Giardia is listed under the category of (a) fungi (b) protozoa (c) bacteria (d) algae

Question 15. Substance used to produce immunity against diseases in the living body is called (a) immune (b) vaccine (c) antibody (d) antigen Answer: 1. (a) 2. (b) 3. (d) 4. (a) 5. (a) 6. (b) 7. (a) 8. (d) 9. (a) 10. (c) 11. (a) 12. (c) 13. (b) 14. (b) 15. (b)

II. Fill in the Blanks Fill in the blanks with suitable word/s. 1. Bacteria, fungi, protozoa and _______ are the major four groups in which microorganisms are classified. 2. Two microorganisms which live in symbiotic association in lichens are _______ and _______. 3. We use a _______ to see the microorganisms. 4. _______ are considered different from other microorganisms because they can multiply only by entering the host organisms. 5. The gas released during the preparation of bread is _______. 6. The disease caused by a protozoan and spread by an insect is _______. 7. _______ are curved-shaped bacteria. 8. Saprophytes and _______ are the two main categories of fungi. 9. _______ are the threads of the multicellular fungi. 10. Yeast is a _______ fungus. 11. Protozoa are _______ in nature. 12. Flu, cough and cold are caused by _______. 13. The first antibiotic discovered was _______. 14. _______ are the microorganisms that help in the process of decomposition. 15. The process of formation of curd from milk is known as the _______ of milk. Answer: 1. algae 2. algae, fungus 3. microscope 4. Viruses 5. carbon dioxide 6. malaria 7. Vibrio 8. parasites 9. Hyphae 10. unicellular 11. heterotrophic 12. viruses 13. penicillin 14. Decomposers 15. curdling

Microorganisms Friend and Foe Class 8 Extra Questions Science Chapter 2 3

IV. True or False State whether the given statements are true or false. 1. Microbiology is the science of study of microbes. 2. All the microorganisms are harmful. 3. An instrument called microscope is required to see the microorganisms. 4. Bacteria have an organised nucleus. 5. Microorganisms are found in large number around us. 6. Viruses are the most useful microbes. 7. Anabaena is listed in the category of algae. 8. Algae tend to develop on wet surfaces. 9. Amoebic dysentery is caused by algae. 10. A fungi is used in the production of alcohol. 11. Jellies, jams and squashes are preserved by adding vinegar to them. 12. Salt is used as a food preservative. 13. Oxygen alone constitutes 78% of air. Answer: 1. True 2. False 3. True 4. False 5. True 6. False 7. False 8. True 9. False 10. True 11. False 12. True 13. False

Extra Questions for Class 8 Science

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  • Published: 03 July 2024

Phenotypic characterization and genomic analysis of a Salmonella phage L223 for biocontrol of Salmonella spp. in poultry

  • Md Abu Sayem Khan 1 ,
  • Zahidul Islam 1 ,
  • Chayan Barua 1 ,
  • Md. Murshed Hasan Sarkar 2 ,
  • Md. Firoz Ahmed 3 &
  • Sabita Rezwana Rahman 1  

Scientific Reports volume  14 , Article number:  15347 ( 2024 ) Cite this article

Metrics details

  • Antimicrobial resistance
  • Bacteriophages

The escalating incidence of foodborne salmonellosis poses a significant global threat to food safety and public health. As antibiotic resistance in Salmonella continues to rise, there is growing interest in bacteriophages as potential alternatives. In this study, we isolated, characterized, and evaluated the biocontrol efficacy of lytic phage L223 in chicken meat. Phage L223 demonstrated robust stability across a broad range of temperatures (20–70 °C) and pH levels (2–11) and exhibited a restricted host range targeting Salmonella spp., notably Salmonella Typhimurium and Salmonella Enteritidis. Characterization of L223 revealed a short latent period of 30 min and a substantial burst size of 515 PFU/cell. Genomic analysis classified L223 within the Caudoviricetes class, Guernseyvirinae subfamily and Jerseyvirus genus, with a dsDNA genome size of 44,321 bp and 47.9% GC content, featuring 72 coding sequences devoid of antimicrobial resistance, virulence factors, toxins, and tRNA genes. Application of L223 significantly ( p  < 0.005) reduced Salmonella Typhimurium ATCC 14,028 counts by 1.24, 2.17, and 1.55 log CFU/piece after 2, 4, and 6 h of incubation, respectively, in experimentally contaminated chicken breast samples. These findings highlight the potential of Salmonella phage L223 as a promising biocontrol agent for mitigating Salmonella contamination in food products, emphasizing its relevance for enhancing food safety protocols.

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Introduction.

Salmonella, a Gram-negative, foodborne zoonotic pathogen, poses a substantial threat to food production and public health globally 1 . Consumption of Salmonella -contaminated foods leads to salmonellosis, an acute infection characterized by symptoms such as fever, nausea, vomiting, and abdominal pain 2 . Non-typhoidal salmonellosis (NTS) accounts for approximately 90 million cases of food poisoning and 155,000 deaths worldwide annually, representing a serious threat to human health 3 , 4 . In the European Union alone, Salmonella is the most frequently isolated pathogen in foodborne outbreaks, contributing to nearly 91,000 cases of salmonellosis annually 5 . Contaminated food items play a major role in around 50% of NTS infections, with fresh-cut produce, raw or undercooked meat, poultry, and eggs being commonly implicated 6 . The prevalence of Salmonella in food varies based on factors such as country, region, food production methods, cultural practices, and geographic location 7 . Furthermore, Salmonella infections can vary in severity depending on the health status of the human host and the serotype involved 8 . Among over 2600 known serotypes of Salmonella , Enteritidis and Typhimurium are the most common food-related serotypes, accounting for half of all salmonellosis cases 9 , 10 .

Although antibiotics are frequently used to control Salmonella infections in humans and veterinary settings, their excessive use has led to an increase in the emergence and transmission of multidrug-resistant (MDR) bacteria over the past decades 11 . In terms of temporal distribution, the prevalence of antimicrobial-resistant (AMR) Salmonella increased from 53 to 77% in South Asia between January 2010 to June 2021 12 . The increase in the occurrence of ESBL-producing non-typhoidal Salmonella in animal and poultry products has become of great concern due to resistance to cephalosporins that are used to treat severe salmonellosis in humans 13 . In addition, the emergence and dissemination of mobilizable and plasmid-borne mcr genes mediated colistin resistance in Salmonella enterica in humans and livestock across different countries threatens the efficacy of colistin, a last-resort antibiotic of the polymyxin family that is indicated for treating invasive infections by multidrug-resistant Enterobacteriaceae in humans 14 . According to epidemiological studies, MDR strains of Salmonella are more virulent than sensitive strains because they cause infections to become more severe 15 . The occurrence of MDR Salmonella not only causes economic loss but also complicates the control of foodborne outbreaks, potentially increasing the number of hospitalizations and mortality rates. Therefore, the need for new antimicrobial agents is of utmost importance to combat Salmonella infections in humans and livestock.

Bacteriophages, the bacteria-killing viruses, have gained renewed attention as an antibacterial for controlling pathogens in food, health and agriculture due to their bactericidal capability, availability in the environment, ease of isolation and cost-effective production characteristics 16 . The unique properties of phages, including their capacity to selectively kill targeted pathogens, non-toxicity to humans, self-replication and self-limiting, make them suitable for use in food safety applications 17 . Moreover, phage treatment of bacterial contamination has some potential advantages over conventional use of antimicrobials. Phages do not harm beneficial microbes in foods and human and animals’ intestinal tracts. Next, it is unlikely that the addition of phages causes negative impacts on food characteristics 18 . A growing body of literature on the isolation, characterization and application of Salmonella phages reported some notable findings in favor of their effectiveness in reducing Salmonella load on a wide variety of foods including eggs, chicken meat, sausage, milk, seafood, lettuce, tomatoes and others. Islam et al. 2019, reported a significant 3log CFU reduction in the viable count of Salmonella in milk and chicken breast after phage treatment at 4 °C and 25 °C. They also observed the anti-biofilm effect of Salmonella phage on microtiter plates and stainless steel 19 . Another study found that application of Salmonella phage LPSE1 at MOI = 1 had reduced the number of recoverable Salmonella by 1.44, 0.52, and 2.02 log CFU on milk, sausage and lettuce, respectively at MOI = 1 20 . A recent study by Park et al., observed that the treatment of chicken milk and meat with phage MSP1 reduced the number of Salmonella below the detection limit 21 . Such promising findings also led to the development of phage-based products. The US Food and Drug Administration (FDA) and the US Department of Agriculture (USDA) have officially approved several commercial phage products for use in food to combat foodborne pathogens such as Salmonella spp., E coli and Listeria monocytogenes 22 . Intralytix Inc, USA developed a cocktail of six phages, SalmoFresh that got FDA approval for direct use in poultry, fish and shellfish, fresh and processed fruits, and vegetables. Salmonelex is another commercial phage preparation that was approved in 2013 as an authorized processing aid for the manufacture of meat and poultry products. In addition, Listex P100 has been granted GRAS (Generally Recognized As Safe) status by the US FDA and endorsed by the Food Safety and Inspection Service for its antimicrobial use in ready-to-eat meat and poultry items 23 . However, the use of phages often has geographical limitations due to the narrow lytic range and distribution of serotypes and therefore, the local scale isolation and application of new phages is necessary 24 .

Salmonellosis remains a major concern in the growth of the poultry industry in Bangladesh with a prevalence of between 28% and 53.3% 25 . In recent years, numerous studies reported the higher occurrence of MDR Salmonella with plasmid-mediated resistance genes in poultry processing environments and related products 26 , 27 , 28 . Such reduced susceptibility to different commonly used antibiotics in poultry due to their indiscriminate use develops treatment failure 29 . In this regard, phages can be a well-suited antibacterial technology for food decontamination, veterinary applications and human treatment in lower- and middle-income countries (LMIC), as Bangladesh 30 . While previous studies in Bangladesh have focused on isolating and characterizing Salmonella phages at a physicochemical level, a comprehensive assessment of their genomic characteristics and suitability for biocontrol applications remains lacking. Recognizing the potential of bacteriophages against antimicrobial-resistant (AMR) Salmonella strains, we isolated a Salmonella phage (L223) from poultry sewage and conducted detailed analyses of its physicochemical stability, replication kinetics, and genomic properties. Furthermore, we assessed the biocontrol efficacy of the isolated phage against Salmonella Typhimurium in chicken meat, aiming to provide valuable insights into its practical application in food safety and public health initiatives.

Phage isolation and characterization

Salmonella phage L223 was isolated from a poultry market sewage sample that produced small (approximately 2 mm), round and lytic plaque on the lawn of Salmonella Typhimurium ATCC14028 (Fig.  1 A). Following isolation, propagation and purification, a stock titer was prepared maintaining a concentration of 10 10  PFU/ml. The latent period and burst size of L223 were estimated to be 30 min and 515 PFU/cell, respectively (Fig.  1 D). It showed stability to a wide range of temperature and pH. Though the optimum temperature was 40 °C, no noticeable variation in phage stability was observed between 20 °C and 40 °C (Fig.  1 B). After that, phage counts tended to decrease and no activity was found at 80 °C. Meanwhile, subjecting phage at pH between 2 and 11 exhibited that phage can tolerate this wide spectrum of acid–base changes. The average phage count at pH between 4 and 10 was 7.9 ± 0.25 log PFU/ml (Fig.  1 C).

figure 1

Different characteristics of Salmonella phage L223. ( A ) Lytic plaque on soft agar; ( B ) Temperature stability of L223; ( C ) Phage stability at different pH and ( D ) One step growth curve.

Isolated phage also infected 3 Salmonella Typhimurium, 2 Salmonella Enteritidis and 2 undetected Salmonella serotypes that were previously isolated from different poultry samples. The EOP of phage L223 in Salmonella Typhimurium and Salmonella Enteritidis ranged from 0.52 to 0.80. However, no lytic activity against bacteria from other species including, E. coli ATCC 25922, Pseudomonas aeruginosa, Vibrio cholerae, Shigella flexneri, Acinetobacter baumanii, and Staphylococcus aureus suggested a narrow host range of phage L223 (Table 1 ).

In vitro bacteriolytic activity of phage L223 was investigated through time-kill curve analysis at different MOIs (1, 0.1, 0.01, and 0.001) up to 360 min (6 h). Compared to phage-free control, bacteriolytic activity was observed at all MOIs based on the measurement of optical density. The optical density at MOI = 1 remained consistent throughout the experimental time, whereas bacterial growth initially increased and tended to decrease after 4 h as evidenced by a reduction in optical density at MOI = 0.1, 0.01 and 0.001 (Fig.  2 ).

figure 2

Bacteriolytic kinetics of Salmonella phage L223 against Salmonella Typhimurium.

Phage genome analysis

The length of the phage genome was 44321 bp of circular dsDNA with 47.9% GC content. According to CheckV, the completeness was 100% (GenBank Accession no.: PP034127). RAST-based genome annotation predicted 72 coding sequences (CDS). Based on the predicted roles of these CDSs, the proteins can be distributed into structural proteins (capsid protein, tail spike protein), replication and regulatory proteins (DNA polymerase, DNA helicase), packaging-associated proteins (terminase) and host cell lysis proteins (holin, endolysin) (Fig.  3 ). The phage genome had no genes for antimicrobial resistance, virulence and tRNA. The lifestyle of the phage, as predicted by BACPHLIP, was lytic (virulent) with a score of 0.9875.

figure 3

Circular genome map of Salmonella phage L223.

Taxonomic assignment, phylogeny and comparative genomic analysis

Genome-wide analysis for taxonomic annotation was enabled by VICTOR and vConTACT2. VICTOR-based whole genome phylogeny predicted that Salmonella phage L223 shared close relation with phages belonging to the Jerseyvirus genus including phage SGPC, S4Iw, pink, SETP13, ZCSE9, wast and jersey (Fig.  4 ). A proteome clustering and network analysis using vConTACT2 designated the L223 phage to viral cluster VC_42 (Fig.  5 ). Phages of this cluster belong to the order: Caudoviricetes class, Guernseyvirinae subfamily and Jerseyvirus genus. The results of VICTOR and vConTACT2 were further reaffirmed by ViPTree and PhageClouds network analysis. The Salmonella phage L223 was predicted to be closely linked to Salmonella phage Jersey, according to a maximum likelihood tree constructed utilizing viral genomes in ViPTree against dsDNA of all genomes. Moreover, based on the computational analysis of the distance relationship between L223 and other phage genomes deposited in NCBI GenBank, L223 was found to be linked to 116 phage genomes at a distance threshold of ≤ 0.2 . Similar to other tools , Phage Cloud also assigned our isolated phage in the Jerseyvirus genus.

figure 4

Phylogenetic analysis of Salmonella phage L223 based on ( A ) genome-BLAST Distance Phylogeny (GBDP) and ( B ) proteomic tree based on genome wide similarities.

figure 5

Phage genome network analysis using vConTACT2. ( A ) Salmonella phage L223 occurs in viral Cluster VC_42 (red colored), ( B ) A closer look on VC_42 cluster.

The linear comparison of phage genomes using Easyfig and intergenomic comparisons with VIRIDIC showed similarity between L223 and top hit phages from blastn search. The intergenomic similarity between L223 and closely related homologs ranged from 75.8 to 81%, suggesting that L223 shared the same genus (> 70%) with compared phages but belonged to different species (< 95%). This finding reaffirmed the result of VICTOR. Even, none of the phages used in comparative genomic analysis had 95% similarity with other phages, indicating they all belong to different species (Fig.  6 ).

figure 6

Comparative genomic analysis of Salmonella phage L223 and closely related phage genomes ( A ) VIRIDIC heatmap, ( B ) Whole genome comparison, and ( C ) PhageCloud analysis.

Pan -genome analysis

Pan-genome analysis of Salmonella phages indicated the presence of 4 core genes (99% ≤ strains ≤ 100%), 7 softcore genes (95% ≤ strains < 99%), 83 shell genes (15% ≤ strains < 95%), and 437 (0% ≤ strains < 15%) cloud genes (Fig.  7 ). Moreover, the openness of the pan-genome was evident from the core-pan rarefaction curve (Fig.  8 ). With the addition of the Salmonella phage genome, the number of pan-genome genes increased gradually. The average nucleotide identity of phages remained between 80 and 100%.

figure 7

Pan-genome matrix of 65 Salmonella phages.

figure 8

Pan-genome analysis of Salmonella phages: ( A ) Distributions of genes in pan-genome, ( B ) Changes in the number of conserved and total genes, ( C ) Changes in the number of new and unique genes, and ( D ) Average nucleotide identity between phages.

Effect of phage treatment on Salmonella Typhimurium on chicken meat

The biocontrol activity of isolated phage was examined on Salmonella Typhimurium ATCC 14028 contaminated chicken breast samples at 25 °C for 2, 4 and 6 h. We observed that the number of hosts was significantly reduced ( p  < 0.005) upon phage treatment of experimentally contaminated chicken breast compared to phage untreated control during different incubation times (Fig.  9 ). After 2 h, phage treatment reduced Salmonella count by 1.24 log CFU/piece compared to non-treatment. However, a maximum of 2.17 log CFU/piece reduction of Salmonella was achieved after 4 h of treatment. Though, the bacterial counts in the phage treated samples at 6 h of incubation were increased, bacterial viabilities were still significantly ( p  < 0.005) lower in the treatment group than those in the phage free control samples.

figure 9

The activity of the phage L223 against Salmonella Typhimurium on chicken meat.

The worldwide increasing prevalence of foodborne salmonellosis, the treatment failure associated with the emergence of MDR Salmonella in veterinary and foods, and the slow progress in the development of new antibiotics have stimulated the efforts to search for alternatives to antibiotics 31 . Lytic phages have now been considered one of the most promising alternatives due to host specificity, ease of application, eco-friendly and cost-effective than antibiotics 32 . A large collection of bacteriophages, the use of obligately lytic phages rather than temperate phages, host range, and screening of phage genomes to validate the lack of toxin genes are some of the characteristics necessary for successful phage therapy in practice 33 . Here, we described the isolation, identification, phenotypic and genotypic characterization, and antibacterial application of a lytic Salmonella phage L223 from poultry environmental sewage in Bangladesh.

Temperature resistance and acid–base changes are some of the most essential characteristics of phage utilized in biocontrol applications in foods and the environment 34 . Phage L223 exhibited a broad range of pH (2–11) and thermal stability (≤ 70 °C). The result is consistent with other studies that also reported similar stability in Salmonella phage SWJM-01 and SWJM-02, PSDA-2, PS5, ZCSE-9 and others 3 , 31 , 35 , 36 . Such stability at a wide temperature and pH range indicated the suitability of L223 for use in food processing and utilization in foods with different pH values (meat, milk, fruits). The latent period and burst size are two crucial parameters in the assessment of phage fitness and the selection of suitable candidate phages for biocontrol and therapeutic applications 37 . Phage L223 exhibited a short latent period (30 min) and a large burst size of L223 (515 PFU/cell) in one step growth curve. This latent time was similar to phage phiPT1, STGO-35-1, AUFM_Sc3 but shorter than a cocktail of four phages including vB_SnwM_CGG4-1, vB_SnwM_CGG4-2, vB_SnwM_CGG3-1 and vB_SnwM_CGG3-2 (53 to 65 min), P22 (45 min) and st104a (60 min) 38 , 39 , 40 , 41 , 42 . Moreover, the burst size of L223 was comparable to BPSELC-1 (500 PFU/cell) but larger than vB_SalP_TR2 (211 PFU/cell), OSY-STA (176 pfu/cell), OSY-SHC (256 PFU/cell), SHWT1 (150 PFU/cell) and others 43 , 44 , 45 . This comparison highlights L223's efficiency in phage replication and release compared to other known phages. Bacteriophages with a broad host range are typically preferred in biocontrol applications, even though there is a chance of unfavorable side effects against non-target species. According to the host range analysis, L223 lysed all seven Salmonella spp. including Salmonella Typhimurium and Salmonella Enteritidis but did not produce plaque against bacteria from other genus, suggesting the specificity of this phage. Serovars Typhimurium and Enteritidis were reported to be the predominant serotypes in poultry and poultry products in Bangladesh 26 , 46 . In addition, mixing different phages, commonly known as phage cocktail, is now the most used method to broaden the host range of phages 31 . The physicochemical stability and multiplication kinetics of L223 suggested that it may have the potential to be used in the formulation of a phage cocktail.

A comprehensive analysis of the phage genome is essential to assess the safety of phages before their use as antibacterial agents. The contribution of phages in the transmission of AMR genes and virulence factors by horizontal gene transfer has been extensively studied. Therefore, phages with AMR and virulence genes are not considered for biological control of pathogens in the food industry. In this regard, whole-genome sequencing can enable the in-depth characterization of phages and thus ensure the security and efficacy of phages for biocontrol applications 47 . The complete genome sequence of L223 consisted of 44321 bp that contained 72 CDS. The genome length of L223 was in alignment with other phages (PSDA-2, ZCSE-9, STGO-35, vB_SenS_TUMS_E4, vB_SenS_SE1) in which the genome size ranged from 40 to 50 kb 31 , 36 , 39 , 48 , 49 . The predicted CDSs were associated with DNA replication, phage assembly and packaging, structural proteins, host cell lysis and other functional domains. In addition to the observation of lytic plaque in soft agar, the presence of holin and endolysin in the phage genome and the prediction of BACPHLIP confirmed the virulent (lytic) nature of L223. Most importantly, the whole genome analysis also confirmed the absence of antibiotic resistance genes, virulence genes, tRNA and lysogenic genes. Therefore, it can be concluded that L223 does not integrate the gene fragments into the host bacteria's genome during its life cycle and does not cause harm to the host when used to treat Salmonella infections. Taxonomic assignment of L223 using VICTOR predicted that it belongs to the Caudoviricetes class, Guernseyvirinae subfamily and Jerseyvirus genus. This taxonomic information was found to be consistent with the prediction from other tools like vConTACT2, ViPTree and VIRIDIC. Phages from the siphoviridae family including, PSDA-2, vB_SenS_SE1, ZCSE-6, S55, SHWT1, vB_SalP_LDW16, vB_SenS_TUMS_34 were well-recognized as promising biocontrol agents as described in literatures 31 , 45 , 48 , 49 , 50 , 51 . Despite the pan-genome analysis provides important insights into the genetic diversity at the species level, studies or pan-analysis on bacteriophages are rare. Pan-genome analysis of 65 Salmonella phages identified 4 core genes and 7 softcore genes that together comprised 2% of all genes. Our finding was in alignment with a study that reported the identification of 2.1% core genes during the pan-genome analysis of 100 phages from the Markadamsvirinae subfamily 24 . Overall, genomic analysis of our phage and subsequent comparisons with other Salmonella phages indicated the safety and suitability of L223 in biocontrol.

We examined the efficiency of phage L223 in reducing the counts of Salmonella Typhimurium in artificially contaminated chicken breast. Bacterial counts were significantly reduced in phage-treated meat at three different incubation times compared to phage-free control. During this experiment, we selected a MOI of 1 because bacteriolytic activity was consistent at that MOI as evident from the optical density in the time-kill curve assay. A 1.24, 2.17, and 1.55 log CFU/piece reduction in Salmonella Typhimurium was achieved when phage-treated meats were incubated for 2, 4, and 6 h, respectively at room temperature. Similar to our findings, Zhou et al., 2021 reported a significant decrease in Salmonella Enteritidis count after 6 h of treatment with Salmonella phage SapYZU01 at MOI = 1 at 25 °C 52 . A comparison of existing studies suggested that several factors including incubation time and temperature, a mixture of multiple phages, mode of phage applications, the multiplicity of infection, type of food matrices, and Salmonella serotype might influence the success of phage treatment in food products. For example, Sun et al., 2022 observed a positive correlation between the decrease in Salmonella Typhimurium and MOI, in which phage PSDA-2 reduced Salmonella contamination in chilled mutton within 120 h of treatment 31 . Reviera et al., 2022 isolated and characterized a Salmonella phage STGO-35-1 that decreased Salmonella Enteritidis counts by 2.5 log in chicken meat at 4 °C 39 . Another phage LPST94 also caused considerable reduction of Salmonella viable counts on chicken breasts with MOI = 1000 and MOI = 10,000 at 25 °C 53 . However, a phage cocktail is proven to be more effective in controlling pathogens compared to individual phages 54 . It also broadens phage host range as well as suppresses anti-phage resistance of pathogens. For instance, treatment of contaminated chicken breast with a cocktail of five phages at MOI = 10 4 reduced the number of Salmonella Typhimurium by 2.0, 1.9, and 2.2 log CFU/piece at 2, 4, and 6 h, respectively 4 , 22 . Gvaladze et al., 2024 sprayed a cocktail of six phages on chicken skin contaminated with Salmonella Enteritidis and the mixed culture and achieved after 30 min a significant 1.8 log and 1 log reduction, respectively 55 . Spricigo et al., 2013 observed that dipping chicken breast for five minutes in a solution containing the bacteriophage cocktail and subsequently chilled at 4 °C for seven days showed significant 2.2 and 0.9 log10 cfu/g reductions in the concentrations of Salmonella Typhimurium and Salmonella Enteritidis, respectively 56 . In comparison, we assume that optimization of those influencing factors might enhance the bacteriolytic capability of L223 and make it more competent for Salmonella control in food and food products.

Materials and methods

Host strain and culture condition.

Salmonella Typhimurium ATCC14028 was used as a host for bacteriophage isolation and characterization. Previously isolated Salmonella Typhimurium, Salmonella Enteritidis and other Salmonella spp. from poultry excreta and eggshells were utilized for phage host range determination 28 . All strains were grown on nutrient agar at 37 °C for 20–24 h. 20% glycerol stock (v/v) of all strains was kept at − 20 °C for storage.

Isolation and propagation of bacteriophage

Five sewage samples were collected from different points of the drainage system of the Kaptan Bazar area, one of the largest retail poultry markets in Dhaka city. Then, samples were subjected to centrifugation at 10,000 rpm for 10 min at 4 °C to remove large particles and the resulting supernatants were filtered through a 0.22 µm syringe filter. Subsequently, 10 ml of filtrate was added to 30 ml log phage Salmonella Typhimurium ATCC14028 (host) culture and incubated overnight at 37 °C. The mixture was again centrifuged at 10,000 rpm for 10 min at 4 °C. Then, the double overlay agar method was used to isolate lytic phage. To do that, 100 µl filtered supernatant was mixed with 100 µl host and added to 0.7% semi-solid agar. Then, the mixture was poured onto prepared nutrient agar (1.5%) and incubated overnight at 37 °C. The bacteriophage’s capacity to produce plaque was observed and plaque-forming units (PFU) were counted. For phage purification, a sterile micro-pipette tip was first inserted into the center of the plaque and swirled to extract a single plaque. The plaque was then pipetted into 100 µl of normal saline and subjected to plaque assay. This procedure was repeated three consecutive times using the same host to obtain host-specific phage. In addition, the same assay was also followed using serially diluted purified bacteriophage to enumerate the number of phages (PFU/ml).

Temperature and pH stability

The pure phage suspension was heat treated at different temperatures ranging from 20 to 80 °C for 1 h to assess the temperature stability of the phage. For determining the pH stability of phage, nutrient broths were prepared by adding NaOH or HCl to maintain pH from 2 to 12. After treatment, phage titers were measured by the double-layer method.

Host range determination

Different Salmonella isolates along with other Gram-negative bacteria including Escherichia coli , Vibrio cholerae , Pseudomonas aeruginosa , Acinetobacter baumannii , and Staphylococcus aureus were tested for phage susceptibility. A 100 µl exponential phase culture of host bacteria was plated by double layer method and allowed the top layer to solidify. Then, a drop of 10 µl phage suspension ( ∼ 10 9  PFU/ml) was spotted on the bacterial lawn and incubated at 37 °C for 24 h. The results of bacterial lysis were recorded to determine the host range. In addition, the efficiency of plating (EOP) was determined against these isolates using plaque assay as described by Hosny et. al. 57 . The average of PFUs on test isolates was divided by the average of PFUs on host bacteria to calculate EOP.

Time-kill curve assay

Characterization of bacterial susceptibility to phage infection at different multiplicities of infection (MOI’s) was done by time-kill analysis 24 . Briefly, the optical density of the freshly grown culture of Salmonella Typhimurium ATCC14028 was set to OD 600  = 0.6 ( ∼ 10 8  CFU/ml). Then, bacterial culture was infected with different concentrations of phage to obtain final MOIs of 1.0, 0.1, 0.01, 0.001, and 0.0001 in a 96-well microplate and incubated at 37 °C. The optical density was measured at 20 min intervals for 360 min (6 h) using Promega GloMax EXPLORER.

One step growth curve analysis

The latent period and burst size of phage L223 were determined through one step growth curve analysis as described by Kropinski et al . with some modifications 58 . Briefly, the host culture was mixed with phage suspension at MOI = 1. The mixture was incubated at 37 °C for 10 min to allow phage absorption. Then, the mixture was centrifuged at 10,000 rpm for 5 min. The resulting pellet was resuspended in 10 ml fresh nutrient broth and kept at 37 °C in an orbital shaker incubator. The phage titer was estimated at 10-min intervals for 60 min by standard plaque assay as described earlier. The time gap between absorption and the start of the first burst was termed the latent period. The burst size was calculated by dividing the final titer of the bacteriophage by the initial titer.

Phage DNA extraction, sequencing and assembly

Bacteriophage DNA was extracted using a DNeasy Blood and Tissue kit (Qiagen, Germany) with some modifications as described by Jakociune et al. 59 . The concentration and purity of DNA were determined with a Nanodrop spectrophotometer and electrophoresis on 1% agarose gel. Then, the extracted phage DNA was subjected to paired-end sequencing using Illumina NextSeq2000 at the Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka. The quality of raw reads was inspected with FastQC ( https://www.bioinformatics.babraham.ac.uk/projects/fastqc/ ). The reads were trimmed using the fastp v0.23.4 ( https://github.com/OpenGene/fastp ) 60 to remove adapters, sequence duplication and low-quality sequences. Finally, SPAdes v3.15.5 ( https://github.com/ablab/spades ) 61 was used to assemble quality filtered reads with careful option. QUAST ( https://github.com/ablab/quast ) 62 was employed to observe the characteristics of the assembled genome. In addition, the completeness of the phage genome was calculated using CheckV ( https://bitbucket.org/berkeleylab/checkv/src/master/ ) v1.0.3 63 .

Bioinformatic analysis of phage genome

The phage genome was annotated using the RAST (Rapid Annotation using Subsystem Technology) ( https://rast.nmpdr.org ) 64 which was further verified using the blastp with an e-value = 0.01. Proksee ( https://proksee.ca/ ) 65 was used to create a circular genome map. The closely related phages were identified with blastn 66 and ViPTree ( https://www.genome.jp/viptree/ ) server (version 4.0) 67 . The phage lifestyle (lytic or temperate), the presence of tRNA were predicted by tRNAscan-SE (version 2.0) ( http://lowelab.ucsc.edu/tRNAscan-SE/ ) 68 and BACPHLIP (default version) ( https://github.com/adamhockenberry/bacphlip ) 69 , respectively. Moreover, ABRicate ( https://github.com/tseemann/abricate ) was used to scan phage genome for bacterial virulence factors and antimicrobial resistance genes using the VFDB 70 , CARD 71 and ResFinder 72 databases. VIRIDIC ( https://rhea.icbm.uni-oldenburg.de/viridic/ ) 73 calculates intergenomic similarities between viral genomes and therefore, was employed in the comparative genome analysis of the assembled phage with its close homologs. The figure of genomic comparison was generated using a freely available tool, Easyfig.

VICTOR (Virus Classification and Tree Building Online Resource) ( https://ggdc.dsmz.de/victor.php# ) 74 , a genome-based phylogeny and classification of prokaryotic viruses, was used for nucleotide-based grouping of phage. A circular proteomic tree was generated using VipTree that utilizes tblastx to compute genome-wide similarities and predicts taxonomic information of viruses and their hosts based on the Virus-Host DB. Moreover, vConTACT v2.0 ( https://kbase.us/applist/apps/vConTACT/vcontact/release ) was utilized for phage taxonomic assignment by performing shared proteome clustering analysis 75 . The association between the sequenced phage genome and other phage sequences on NCBI-GenBank was visualized using PhageClouds ( https://phageclouds.ku.dk/ ) 76 , with a threshold of 0.2 for intergenomic distances. Finally, the pan-genome analysis of 65 Salmonella phages, belonging to the same family of Salmonella phage L223 with S G  ≥ 0.8 (VipTree) was performed using Roary v.3.11.2 ( https://sanger-pathogens.github.io/Roary/ ) 77 .

Application of bacteriophage

The isolated phage was applied on experimentally infected meat to assess its ability to reduce Salmonella Typhimurium ATCC14028 following the protocol described by Duc et al. with some minor modifications 22 . Commercially available chicken breast meat was purchased from the supermarket. The absence of Salmonella in meat samples was done by plating serially diluted homogenized meat on XLD agar. Then, the meat sample was cut into small pieces (3 × 3 cm). Both sides of the sliced meat were washed with 70% ethanol. Then, the meat pieces were placed onto a sterile petri plate and treated with UV for 1 h. 100 µl of bacterial suspension (10 8  CFU/ml) was inoculated homogenously onto the meat samples. Then, the meat samples were kept at room temperature for 10 min in a biosafety cabinet to allow bacterial attachment. Bacteriophage titer was diluted to approximately 10 8  PFU/ml to maintain the MOI = 1. 100 µl of bacteriophage suspension was applied on the surface of experimentally infected meat. For the meat pieces in the control group, 100 µl of normal saline was inoculated instead of bacteriophage. The meat pieces were incubated at 25 °C and bacterial count from both control and treatment groups was taken at 2, 4 and 6 h of incubation. The meat pieces were homogenized with 5 ml of saline. The serially diluted homogenate was spread on XLD agar and incubated at 37 °C for 24 h. Following incubation, viable counts of Salmonella in the control and treatment meat pieces were compared to determine phage treatment efficiency.

Statistical analysis

All the experiments were conducted three times. Bacterial counts (log CFU/ml) and phage plaques (log PFU/ml) were tabulated as mean ± SD (standard deviation). The differences between treatment and control groups were determined by t-test using Prism 8 (GraphPad). p -value less than 0.05 was considered statistically significant.

In this study, we isolated a Salmonella phage L223 that exhibited good physicochemical stability, a short latent time with a high burst size, and a strictly lytic lifestyle. The analysis of the phage genome indicated the safety of L223 in biocontrol applications. Finally, an assessment of the antibacterial efficacy in chicken meat resulted in significant reductions in Salmonella Typhimurium ATCC14028 counts. Despite these promising findings, the lack of data on the optimization of parameters during L223 application on meat remains a limitation of the study. Experimentation with an extended range of MOI, time and temperature might provide more insights into the suitability of the therapeutic supplementation of L223. However, taken together, the findings of our study will initiate the development of phage-based products to combat MDR Salmonella in the food industry in Bangladesh.

Data availability

The complete genome sequence of Salmonella phage L223 is available on NCBI Genbank under the accession number PP034127.

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Acknowledgements

We acknowledge Bangladesh Bureau of Education Information and Statistics (BANBEIS), Ministry of Education, Bangladesh for a research grant (LS2018791) to conduct this study.

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Md Abu Sayem Khan, Zahidul Islam, Chayan Barua & Sabita Rezwana Rahman

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Khan, M.A.S., Islam, Z., Barua, C. et al. Phenotypic characterization and genomic analysis of a Salmonella phage L223 for biocontrol of Salmonella spp. in poultry. Sci Rep 14 , 15347 (2024). https://doi.org/10.1038/s41598-024-64999-1

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Differential reshaping of skin and intestinal microbiota by stocking density and oxygen availability in farmed gilthead sea bream ( sparus aurata ): a behavioral and network-based integrative approach.

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1. Introduction

2. materials and methods, 2.1. ethics statement, 2.2. experimental setup and sampling, 2.3. nucleic acid extraction, 2.4. nanopore 16s rrna gene sequencing and bioinformatic analysis, 2.5. illumina 16s rrna gene sequencing of gut mucus samples and bioinformatics analysis, 2.6. host intestinal rna sequencing and bioinformatic analysis, 2.7. statistics and visualizations, 3.1. skin mucus composition and diversity analysis, 3.2. skin mucus correlation network, 3.3. intestinal microbiota composition and diversity analysis, 3.4. intestinal wide-transcriptomic analysis, 3.5. intestinal mucus correlation network, 4. discussion, 5. conclusions, supplementary materials, author contributions, data availability statement, acknowledgments, conflicts of interest.

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Toxqui-Rodríguez, S.; Holhorea, P.G.; Naya-Català, F.; Calduch-Giner, J.À.; Sitjà-Bobadilla, A.; Piazzon, C.; Pérez-Sánchez, J. Differential Reshaping of Skin and Intestinal Microbiota by Stocking Density and Oxygen Availability in Farmed Gilthead Sea Bream ( Sparus aurata ): A Behavioral and Network-Based Integrative Approach. Microorganisms 2024 , 12 , 1360. https://doi.org/10.3390/microorganisms12071360

Toxqui-Rodríguez S, Holhorea PG, Naya-Català F, Calduch-Giner JÀ, Sitjà-Bobadilla A, Piazzon C, Pérez-Sánchez J. Differential Reshaping of Skin and Intestinal Microbiota by Stocking Density and Oxygen Availability in Farmed Gilthead Sea Bream ( Sparus aurata ): A Behavioral and Network-Based Integrative Approach. Microorganisms . 2024; 12(7):1360. https://doi.org/10.3390/microorganisms12071360

Toxqui-Rodríguez, Socorro, Paul George Holhorea, Fernando Naya-Català, Josep Àlvar Calduch-Giner, Ariadna Sitjà-Bobadilla, Carla Piazzon, and Jaume Pérez-Sánchez. 2024. "Differential Reshaping of Skin and Intestinal Microbiota by Stocking Density and Oxygen Availability in Farmed Gilthead Sea Bream ( Sparus aurata ): A Behavioral and Network-Based Integrative Approach" Microorganisms 12, no. 7: 1360. https://doi.org/10.3390/microorganisms12071360

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  1. Types of Microorganisms- Class 8 Science Guide

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  2. CBSE Class 8 Science Worksheet (3)

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  3. Microorganisms

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  4. Microorganisms Friend And Foe

    assignment of microorganisms class 8

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    assignment of microorganisms class 8

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    assignment of microorganisms class 8

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  1. Microorganisms- Vaccines,Antibiotics & Food Preservation🦠|Chapter 3 Class 8 Science🔥|Diksha Bhuwalka

  2. Top 10 Important Questions from Microorganisms Friend and Foe Class 8 Science Chapter 2

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  4. MICROORGANISMS Part

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COMMENTS

  1. Microorganisms Class 8 Notes

    CBSE Class 8 Science Chapter 2 Notes: Microorganisms. If you observe a drop of water in a pond through a microscope, you will see a lot of tiny rounded structures. These tiny creatures are known as microbes or microorganisms. They are all around us and are so small in size that they cannot be seen with bare human eyes.

  2. Important Questions for CBSE Class 8 Science Chapter 2

    Download and add these Class 8 Science Chapter 2 Microorganisms: Friend and Foe questions and answers to your study material in the form of a downloadable PDF. Pay attention to the answers and learn how to use them to your advantage. Fill in the spaces with these questions and answers to assess your level of readiness.

  3. NCERT Solution for Class 8 Science Chapter 2 FREE PDF

    Our materials provide clear and detailed explanations, which makes it ideal for anyone studying this chapter. Table of Content. 1. NCERT Solutions for Class 8 Science Chapter 2- Microorganisms Friend and Foe Free PDF Download. 2. Quick Insights for NCERT Class 8 Science Chapter 2 Question Answer PDF. 3.

  4. NCERT Solutions For Class 8 Science Chapter 2 Microorganisms

    NCERT Class 8 Science Chapter 2 thoroughly examines the various functions that microorganisms perform in ecosystems and our daily lives. The chapter highlights the useful functions of microbes, including their importance to environmental processes. The detrimental effects of some microbes, referred to as pathogens, which cause illnesses in ...

  5. NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend

    The NCERT Solutions for Class 8 Science Chapter 2 are important study materials for the students of the 8th standard. These answers will help them to attain perfection on the concepts involved in the chapter Microorganisms: Friend and Foe as listed above. Keep visiting BYJU'S for the latest CBSE sample papers and previous years' question ...

  6. Revision Notes For CBSE Class 8 Science Chapter 2

    Also, check CBSE Class 8 Science revision notes for other chapters: CBSE Class 8 Science Chapter-wise Notes. Chapter 1: Crop Production and Management Notes. Chapter 2: Microorganisms: Friends and Foe Notes. Chapter 3: Synthetic Fibres and Plastics Notes. Chapter 4: Materials : Metals and Non-metals Notes.

  7. Microorganisms Class 8 Notes, Question Answers

    Microorganisms Class 8 Science Chapter 2 as per NCERT Book used in CBSE and other Schools. The lesson covers the complete explanation of class 8 Chapter 2 Microorganisms.Topics covered are Introduction to Micro-organisms and microbiology, different types of Micro-organisms, Useful and Harmful Micro-organisms. How to avoid the spreading of Microorganisms has been discussed.

  8. CBSE 8, Science, CBSE- Microorganisms

    2 marks. Download free CBSE Sample paper for Class 8, Science. A collection of questions on CBSE- Microorganisms - Friend and Foe with solutions created by best teachers are available as a PDF download.

  9. CBSE 8, Science, CBSE- Microorganisms

    Microorganisms - Friend and Foe-Notes. Microorganisms- A living organism that is very minute to be seen by the naked eye, especially a single celled organism, such as a bacterium is called microorganism. Microorganisms are classified into four major groups mainly bacteria, fungi, protozoa and some algae.

  10. Class 8 Micro-organisms Friend and Foe Worksheets

    This Class 8 Microorganisms Friend and Foe Worksheets is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail. Also Read. Notes. Micro-organisms Friend and Foe Class 8 Notes; Assignments ...

  11. Microorganisms: Friend and Foe Class 8 Notes Science Chapter 2

    CBSE Class 8 Science Notes Chapter 2 Microorganisms: Friend and Foe. Microorganisms are too small and are not visible with the naked eye. They can live in all kinds of environment, ranging from ice cold climate to hot springs, deserts and marshy lands. Microorganisms are found in air, water and in the bodies of plants and animals.

  12. Basic Lesson Plan Class 8 Microorganism Friend and Foe

    This document outlines a lesson plan on microorganisms for an 8th grade biology class. It discusses how microorganisms can be both helpful and harmful. It will teach students about the classification of microorganisms including bacteria, fungi, protozoa, algae, and viruses. It will also discuss how some microorganisms are useful in food production, agriculture, and medicine, while others can ...

  13. NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and

    NCERT Solutions for Class 8 Science Chapter 2 - 5 Mark Questions and Answers. Question 1. Describe the nitrogen cycle with the help of a neat and labelled diagram. [MSE (Chandigarh) 2005, 2007] Answer: Question 2. Write 10 lines on the usefulness of microorganisms in our lives. [NCERT] Answer:

  14. PDF Chapter 2 Microorganisms: Friend and Foe Notes

    Harmful Microorganisms: (i) Some of microorganisms are harmful in many ways. (ii) In human beings, plants and animals, some of the microorganisms cause diseases. Such disease-causing microorganisms are called pathogens. (iii) Food, clothing and leather are spoiled due to some harmful microorganisms. Disease— causing Microorganisms in Humans:

  15. NCERT Solutions for Class 8 Science Chapter 2 Microorganisms: Friend

    Answer: (a) Microorganisms can be seen with the help of a microscope. (b) Blue green algae fix nitrogen directly from air to enhance fertility of soil. (c) Alcohol is produced with the help of microorganisms. (d) Cholera is caused by bacteria. Question 2: Tick the correct answer: (a) Yeast is used in the production of.

  16. Grade 8 Microorganisms: Friend and Foe Worksheets

    Grade 8 Microorganisms: Friend and Foe Worksheets. November 11, 2020 November 10, 2020 by worksheetsbuddy_do87uk. ... CBSE Worksheets for Class 8: CBSE Worksheets for Class 9: CBSE Worksheets for Class 10: CBSE Worksheets for Class 11: CBSE Worksheets for Class 12: Worsheets for Class 7 Science:

  17. Microorganisms: Friend And Foe Class 8 Science Extra Questions and Answers

    Answer: Aedes mosquito acts as carrier of dengue virus. Question 3: Name any two diseases that can be prevented by vaccination. Answer: Polio and smallpox. Question 4: Give two examples of algae. Answer: Chlamydomonas and Spirogyra. Question 5: Give two examples of protozoa. Answer: Amoeba and Paramecium.

  18. NCERT Exemplar Class 8 Science Solutions Chapter 2

    NCERT Exemplar Solutions Class 8 Science Chapter 2 - Free PDF Download. NCERT Exemplar Solutions for Class 8 Science Chapter 2 Microorganisms: Friend and Foe will assist students in cross-checking their knowledge on various concepts and topics in Microorganisms. Students who are planning to take the annual exam should study this NCERT Exemplar Solutions Class 8 Science thoroughly to ...

  19. PDF W O Rks He E T

    2. What is the role of microorganisms in enriching the soil? 3. Name two antibiotics obtained from fungi and discuss their role. 4. Discuss, how microorganisms play a vital role in agriculture. 5. Microorganisms are found everywhere in our environment. Explain. E . G i v e r e a s o n s fo r th e fo l l o w i n g . 1.

  20. Microorganisms: Friend and Foe Class 8 Extra Questions Science Chapter

    Microorganisms: Friend and Foe Class 8 Extra Questions Higher Order Thinking Skills. Question 1. Unscramble the jumbled words underlined in the following statements. (a) Curbossulite is an air-borne disease caused by a bacterium. (b) Xanrhat is a dangerous bacterial disease.

  21. CBSE Class 8 Science Worksheet

    This document contains questions from a science assignment on microorganisms for class 8 students. It asks students to identify different types of microbes like bacteria, fungi and viruses. It also asks students about microbes that are beneficial like those involved in nitrogen fixation or curd formation. Students are asked about pathogenic microbes that cause diseases in humans and plants ...

  22. Phenotypic characterization and genomic analysis of a ...

    In vitro bacteriolytic activity of phage L223 was investigated through time-kill curve analysis at different MOIs (1, 0.1, 0.01, and 0.001) up to 360 min (6 h). Compared to phage-free control ...

  23. Microorganisms

    Fish were kept for six weeks at three different initial stocking densities and water O2 concentrations (low-LD, 8.5 kg/m3 and 95-70% O2 saturation; medium-MD, 17 kg/m3 and 55-75% O2 saturation; high-HD, 25 kg/m3 and 60-45% O2 saturation), with water temperature increasing from 19 °C to 26-27 °C. The improvement in growth performance with the decrease in stocking density was related ...