Story Of Micro Organisms-1 Class 8th Biology AP Board Solution

Class 8th Biology AP Board Solution

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Question 1.

Which organisms are interlinked between living and non living organisms? Why do you think so?


Viruses are a group of organisms which act as interlink between living and nonliving organisms. We think so because viruses are a group of organisms which exhibit characteristics both of living organisms and of nonliving organisms. Viruses are a special kind of case which exhibits properties intermediate of both.

They exhibit living characteristics in the following manner:

● Viruses have genetic material as the entire living organism possess and it can be RNA or DNA, and this nucleic acid i.e. genetic material remains protected by a covering called protein capsid.

● They are able to replicate and can synthesize nucleic acids and proteins but for all this, they require a host, another living organism whose biosynthetic machinery they will utilize for their propagation and survival.

They exhibit nonliving characteristics in the following manner:

● Unless they don’t get any living host they are not able to replicate and propagate, therefore in absence of a living host, they will act as nonliving organism since they don’t exhibit the property of replication.

Since they can exhibit the behavior of living organisms after entering into a living host and as a non-living organism in absence of a living host, viruses are considered as an interconnecting link between the living and nonliving organisms.

Question 2.

What are micro-organisms? Do you find them?


The name MICRO-ORGANISM itself provides a definition of itself.

Micro- It refers something which is very small in size and can’t be seen with naked eyes or unaided eyes.

Organism- a living entity

Therefore, Microorganisms are the organisms very small in size which we can’t see with naked eyes and require aids like a magnifying glass, microscope etc in order to see them.

Yes, we find microorganisms as they are found everywhere in nature.

A microorganism is a life form which exhibits extreme diversity. They are found everywhere from our body to everything that we see around us.

For example- The curd we eat contains tons of bacteria into it called lactobacillus.

The soil contains a variety of microorganisms into it.

The fecal material also contains bacteria into it.

Question 3.

What type of micro organisms can we observe in pond water?


We can observe bacteria, protozoa, and algae in pond water. Bacteria, protozoa, and algae are different classes of microorganisms.

Bacteria are found everywhere and are also present in a great amount in pond water.

Protozoa like an amoeba, paramecium are also found in pond water.

Algae like Chlorophyta also remain present in abundance.

Question 4.

Whether micro-organisms are useful and harmful. How to explain.


Microorganisms are both a friend and a foe for us. It is said because they are very much beneficial to us in some terms and are also harmful in some cases.

So, due to this dual nature of microorganisms are said to be both a friend and a foe for us.

Microorganisms are useful to us because they help in processes like-

● Fermentation- This process uses a diversity of microorganisms which is used for the production of different products in food and alcohol industry.

● Curd formation- For making curd we always add a small amount of curd as inoculums into the milk which converts complete milk into the curd. Lactobacillus bacteria play a role in it.

● Medicinal use- Microorganisms helps in the production of vaccines and antibiotics and thus helps mankind.

● Micro biota in our body- Our body also contains a variety of microorganisms inside it which helps our body in some way or the other.

For example- Gut microbiota helps in digestion of some dietary fibers.

● Decomposition- Bacteria and fungi act as decomposers and help in the conversion of organic waste into inorganic matter and thus help in the cleaning of the environment.

● The increment in soil fertility- Different microorganisms play important role in increasing the soil fertility. There are certain bacteria like Rhizobium, nostoc, which helps in nitrogen fixation and thus improves the fertility of the soil.

● Pesticides- There are some bacteria like Bacillus thuringinesis which help in the killing of pests by producing toxins and thus protects different crops.

● Genetically modified organisms- Bacteria like E.coli are used for genetic modifications due to their simpler organization and thus contribute to genetic engineering which is an important technology for mankind.

Now we will look at some points how microorganisms are harmful to us. Following are points which will depict the harmful nature of microorganisms:

● Disease in Human beings, animals, and plants- There are certain microorganisms which cause disease and they are termed as pathogens. There are many microorganisms which cause a deadly disease in humans, plants, and animals etc.

● Food poisoning- It is another harmful aspect of microorganisms in which microorganisms cause spoilage of food. They grow on food produce certain toxins which cause spoiling of food.

● Water pollution- Microorganisms also cause water pollution.

Microscopic algae grow in different water sources and cover the entire water source and this process is known as algal bloom. Algal bloom also causes the death of aquatic life as it creates hypoxic condition i.e. lack of oxygen due to which other aquatic life forms get die.

So, due to above-mentioned reasons microorganisms are both useful and harmful to us.

Question 5.

How are the human actions causing the death of useful bacteria and fungi? What will happen if it continuous?


With our day to day activities we are causing harm to useful bacteria and fungi in different ways which are as follows:

● Nowadays there is a great increase in the use of pesticides and fertilizers and farmers are using them in a blind manner without thinking of the fact that how much adverse effect they are causing. Fertilizers kill the microorganisms present in soil which play important role in improving soil fertility.

● Great use of pesticides along with killing pests is killing microorganisms.

● With the increasing industrialization, we dump the industrial wastes in different water sources or in land pits. But this processes of dumping wastes by disturbing the complete soil structure and leaching of harmful chemicals in water sources causes killing of microbial diversity which along with benefitting humans are also beneficial to different life forms present in soil and water sources.

If this process will continue mankind have to pay the great cost for it.

● The killing of various bacteria of soil lead to a decrement in soil fertility and thus we were not able to grow various crops.

● Our plants will also suffer from lack of nutrients as various microorganisms form a symbiotic association with the plants and provide essential nutrients to them.

● Since we are killing the bacteria and fungi which act as decomposers, the absence of them will lead to a huge amount of organic waste accumulating everywhere.

● Being a part of the ecosystem they also contribute to various nutrient cycles of the earth like nitrogen cycle by causing nitrogen fixation, carbon cycle. The killing of them will also disturb the ecosystem.

So, looking at the beneficial part of microorganism and harmful impact that we will have due to their extinction, we should always avoid those actions which cause killing of microbial diversity.

Question 6.

Why the cooked food spoils soon but not uncooked food. Give your reasons.


There are certain conditions which are very much favorable for the growth of the microorganisms. Cooked food provides all those favorable conditions to the microorganisms for their growth which is not provided by raw food.

In cooked food there is moisture due to water, the temperature is also appropriate which is suitable for growth of microorganisms and also an appropriate pH. This all conditions which are basic requirements for the growth of microorganisms are fulfilled by the cooked food more easily as compared to uncooked food.

So, microorganisms grow and cause spoilage of cooked food whereas raw food lacking all these conditions does not get spoil.

Question 7.

What questions would you like to ask your teacher to know about different shapes of Bacteria?


I would like to ask following questions about different shapes of Bacteria to my teacher:

● Do bacteria exist in different shapes?

● What advantages does the shape of bacteria confer to them?

● Why don’t all bacteria have one fixed shape?

● Does altering the shape of bacteria can help us to kill the bacteria or causing any harm to it?

● Does shape of bacteria is in some way related to its motility?

● Does in a different stage of their lives bacteria exhibit different shapes or they exhibit the same shape during their complete life cycle?

● Does their shape also contribute in their microscopic nature?

Question 8.

What will happen if you add buttermilk to chilled milk?


Normally when we add buttermilk to the milk at normal temperature or to the lukewarm milk we observe that after some duration milk gets changed into curd but the same thing doesn’t happen when buttermilk is added to the chilled milk. There will be no transformation of the milk into curd in case of chilled milk.

It happens because the conversion of milk into curd requires lactobacillus bacteria but chilled milk doesn’t provide the appropriate temperature that is required by the lactobacillus bacteria in order to grow.

Since there is no appropriate temperature for lactobacillus bacteria to grow, there is no growth of lactobacillus and chilled milk won’t convert into curd but there will be slight changes in its taste due to the presence of small amount of lactobacillus bacteria.

Therefore, when we add buttermilk to chilled milk there will be no change in it except a slight change in taste.

Question 9.

How do you observe Lactobacillus bacterium?


Since, lactobacillus is a microorganism we can’t see it with unaided eyes. In order to see lactobacillus bacteria we need to observe it under the microscope and for observing under the microscope we need to prepare the slide of buttermilk.

We will follow following steps for the slide preparation:

● Take a clean glass slide.

● Take drop equivalent buttermilk on the slide and spread it using an inoculation loop in order to get a thin smear for better visualization. If we won’t spread it we won’t be able to get a better picture.

● Now, we need to heat fix the bacteria in order to cause their fixation. We will slightly heat the slide for 2-3 seconds and don’t let it get burn.

● Allow it to cool and add 2 drops of crystal violet in order to stain them. Wait for 1 minute. Don’t add excess amount of crystal violet as it will cause over staining.

● Wash the slide with distilled water in order to remove extra stain.

● Clean the other portion of slide using tissue paper and let it air dry.

● After that observe the slide under compound microscope.

Using above steps we can observe the lactobacillus bacteria.

Fig: Lactobacillus bacteria under the microscope

Question 10.

Visit any bakery or milk chilling center near your school with the help of your teacher or parents. Learn about some techniques to culture and usage of some Microorganisms and prepare a note on them.


After visiting bakery and milk chilling center I found that they use the following techniques:

● Pasteurization: In this technique, milk is boiled at very high temperatures and then kept in extremely low temperatures.

These temperatures prevent the growth of microorganisms and thus help in storage of milk in chilling centers.

● Fermentation: This process is used in a bakery where yeast and microorganisms are used to rises the dough of various bakery products. As they produce carbon dioxide and other gases it provides distinct taste to bakery products.

● Baking: In this process, dry heat is provided to the doughs raised by yeast and microorganisms in order to make their outer surface hard and inner surface soft.

Microorganisms used in the bakery are as follows:

● Saccharomyces cerevisae: This is known as baker’s yeast and helps in the fermentation process in the bakery.

● Acetobacter: It is used in the production of vinegar and chocolates.

● Aspergillus: It is used in the formation of soy sauce.

● Bifidobacterium: It is used in the formation of yogurt.

Question 11.

Observe some permanent slides of microorganisms in your school lab with the help of a microscope. Draw its picture.


Question 12.

Prepare a model of any microorganism. And write a note on them.


A model of amoeba as shown below can be prepared.

Amoeba is a single cell microscopic organism which is found in water bodies.

It always keeps on changing its shape with the help of the pseudopodia. (Pseudo-false and podia-feet) i.e. amoeba have this false feet which help it to continuously change its shape and capture its food.

Being unicellular all functions of amoeba are performed by a single cell.

It consists of the following parts:

● Cell membrane: Cell of amoeba is lined by a thin layer which allows passing of materials through it selectively.

● Pseudopodia: As told above pseudopodia are false feet present in amoeba. These are kind of outgrowths which help it to move, change its shape and capture its food. With the help of pseudopodia it takes its food.

● Cytoplasm: This is the liquid substance present within the cell. It is also responsible for the formation of pseudopodia. The cytoplasm contains nucleus and vacuoles inside it.

● Nucleus: It controls all activities of amoeba. It is also surrounded by a membrane.

● Contractile vacuole: It regulates the quantity of water present in cell.

● Food vacuole: It stores the food taken by amoeba.

Amoeba is also able to cause diseases. It causes disease like amoebiasis.

Question 13.

Why should we clean our hands with soap before eating?


We should clean our hands with soap before eating due to following reasons:

● If we will not clean our hands with soap we will get affected by certain diseases. Certain microbes will enter our body through food and will cause diseases.

● Cleaning of hands with soap will act as a disinfection process and kill microbes present on our hands and thus protect us from diseases.