Lesson: Microorganisms: Friend and Foe
Topic 1

# Question: 1

What are microorganisms?

## Solution:

Microorganisms are very small living organisms around us which we can see only with a microscope or magnifying glass. They are also called microbes.

# Question: 2

What are the different shapes of bacteria?

## Solution:

There are mainly four common shapes of bacteria:

a.       Spherical

b.      Comma-shaped

c.       Rod-shaped

d.      Spiral

# Question: 3

Why are viruses considered on the borderline between living and non-living organisms?

## Solution:

Viruses are non-living outside living cells but grow and multiply inside living cells. So, they are considered on the borderline between living and non-living organisms.

# Question: 4

Name the microorganism that reproduces only inside the living cells of other organisms.

Virus

# Question: 5

List the major groups of microorganisms.

## Solution:

The major group of microorganisms are:

a)      Bacteria

b)      Fungi

c)      Protozoa and

d)      Algae

Topic 2

# Question: 1

List some examples of microorganisms that help us in preparing food items.

## Solution:

Microorganisms which help in preparing different food items are as follows:

·         Bacteria help in preparing curd from milk.

·         Yeast is used in the preparation of cakes, breads, biscuits and other bakery products.

·         Bacteria are involved in the making of cheese.

·         Fermentation by bacteria is involved in making batter for idlis and dosas.

# Question: 2

Microorganisms help clean the environment. How?

## Solution:

We often see dead organic matter in the form of decaying plants and animals on the ground. This decaying matter disappears over time due to the fact that microorganisms decompose dead organic waste of plants and animals by microbial action and convert it into simple substances. Thus, microorganisms help clean up the environment.

# Question: 3

What are biological nitrogen fixers?

## Solution:

Plant cannot get nitrogen directly from the atmosphere and have to rely on nitrogenous compounds in the soil to fulfil their needs. Nitrogen-fixing bacteria are capable of transforming atmospheric nitrogen into fixed nitrogen, which are inorganic nitrogenous compounds usable by plants. These nitrogen-fixing bacteria are commonly biological nitrogen $–$ fixers, for example, blue-green algae and symbiotic bacteria such as Rhizobium.

# Question: 4

What do you understand by fermentation?

## Solution:

The process of conversion of sugar to alcohol by microorganisms such as yeast is known as fermentation.

# Question: 5

How are microorganisms useful in protecting us from diseases?

## Solution:

Microorganisms play an important role in protecting the body from diseases. Substances released by certain microorganisms to kill other organisms are used in preparing antibiotic, for example penicillin released by fungi kills bacteria. Antibiotics are chemicals which kill disease-producing bacteria, for example, streptomycin is an effective antibiotic against tuberculosis.

# Question: 6

What would you give to a sick person for treatment $–$ an antibiotic or a vaccine? Justify your answer?

## Solution:

It is advisable to give antibiotics to a sick person for immediate action against a disease-causing pathogen. Vaccines on the other hand are a preparatory defence method, that is, they are given before the person is affected by specific disease-causing pathogens. In the case of some diseases, such as polio, only a vaccine can be used as prevention, but there is no antibiotic cure.

# Question: 7

What are antibodies?

## Solution:

Antibodies are chemicals the body produces when attacked by disease-carrying pathogens. The antibodies fight and destroy the pathogens. They remain in the body and protect it from those pathogens if they invade the body again.

# Question: 8

Why don’t you need to be vaccinated every year?

## Solution:

A vaccine consists of dead or weakened disease-causing microbes, which, once introduced into a healthy body, prepare the body’s defences to produce specific antibodies against those microbes. These antibodies remain in the body and protect it from the microbes in the future also. That is why you do not need to be vaccinated every year.

# Question: 9

Explain the role of microorganisms in the nitrogen cycle.

## Solution:

Microorganisms play an important role in the nitrogen cycle as follows:

Nitrogen fixation: Certain bacteria and blue-green algae present in the soil fix atmospheric nitrogen directly and convert it to nitrogenous compounds used in the synthesis of plant proteins, which are further passed on to animals.

Decomposition of nitrogenous wastes: When plants and animals die, certain soil bacteria and fungi decompose the nitrogenous wastes to nitrogenous compounds, which are reused by plants.

Release of free nitrogen into the atmosphere: Certain other bacteria act on these nitrogenous compounds, producing nitrogen gas, which is released back into the atmosphere.

In this way, microorganisms play a crucial role in the nitrogen cycle.

# Question: 10

Which microorganisms can fix atmospheric nitrogen in the soil? Why is nitrogen fixation important?

## Solution:

Plants cannot absorb nitrogen directly from the air. Bacteria such as Rhizobium and certain blue-green algae present in the soil can fix atmospheric nitrogen directly and convert it to usable nitrogenous compounds. Plants use these nitrogenous compounds and synthesise plant proteins and other compounds. We get these plant proteins by consuming these plants.

Topic 3

# Question: 1

What are pathogens?

## Solution:

Diseases in human beings, plants and animals are mostly caused by microorganisms. These disease-causing microorganisms are called pathogens.

# Question: 2

What are communicable diseases? Give examples.

## Solution:

Communicable diseases are infectious diseases which are spread to a healthy person by direct contact with an infected person through air, water, food or physical contact. Examples are cholera, the common cold, chicken pox, and tuberculosis. The disease transmitter may be a vector transmitter, which merely transports the disease but will not have any traces of the disease in its immune system, as in the case of a mosquito carrying germs of malaria. Alternatively, a carrier could be a disease transmitter which carries the infectious agent but will not show symptoms of it, as in the case of a human who has HIV, but not AIDS.

# Question: 3

How are microorganisms harmful?

## Solution:

Microorganisms are harmful in the following ways:

a.                   Pathogens for diseases in humans and animals - Microorganisms cause diseases in humans and animals. For example, in humans, bacteria cause tuberculosis, cholera, typhoid, etc. In cattle, the foot-and-mouth disease is caused by a virus, while anthrax is caused by bacteria.

b.                  Pathogens for diseases in plants - Several microbes cause diseases in plants, affecting their yield. Examples of plant diseases are citrus canker caused by bacteria and rust of wheat caused by a fungus.

c.                   Spoilage of food and food poisoning - Microbes are also responsible for spoilage of food, resulting in a foul smell and a bad taste. Microbes also produce toxins, making the food poisonous. If you consume such spoilt food, it may cause food poisoning, resulting in nausea, vomiting, diarrhoea and even death.

# Question: 4

What causes food poisoning?

## Solution:

Food poisoning is caused due to the consumption of food spoilt by microorganisms. Microorganisms grow in food items which are not stored and preserved properly, producing toxins. These toxins can cause serious illness and even death on consumption.

# Question: 5

Who first developed the process of preserving milk? Explain the process.

## Solution:

Louis Pasteur first developed the process of preserving milk, which is called pasteurisation. In this process, milk is first heated to about 70°C for 15 to 30 seconds, which kills many microorganisms. Then, the milk is instantly chilled and stored, which prevents further growth of microorganisms. In this manner, pasteurisation helps to prevent spoilage of milk.

# Question: 6

What are the preventive measures against chicken pox?

## Solution:

The preventive measures against chicken pox are as follows:

Stay away from other family members who have not had chicken pox.

Wash clothing that is soiled with fluid from chicken pox blisters.

Keep the patient’s belongings separate.

Get vaccinated.

# Question: 7

What are the preventive measures against polio?

## Solution:

Polio can be prevented through immunisation. Being a highly infectious disease caused by a virus, it invades the nervous system and can cause irreversible paralysis. Polio is spread through person-to-person contact. Therefore, improved public sanitation and careful personal hygiene may help reduce the spread of polio.

# Question: 8

What are the preventive measures against typhoid?

## Solution:

The preventive measures against typhoid are as follows:

Drink filtered water

Maintain proper sanitation

Eat fresh and properly cooked food.

Keep personal items separate from other people in the household.