Science Question Answer (3 Marks)

The spreading of diseases by mosquitoes can be prevented by following ways:

1. We should not let water collect anywhere in the neighborhood.
2. We should keep our surrounding clean and dry.
3. Mosquito repellant creams should be applied on the exposed parts of the body.

Mosquito acts a carrier of disease-causing micro-organism and spreads diseases from one person to another. They carry disease-causing micro-organisms (microbes) inside its body. Female Anopheles mosquito is a carrier of malarial parasite. When it bits a person suffering from malaria, it sucks the blood of that person which contains the malarial parasite microbes. When this infected mosquito bites a healthy person, it transfers the microbes into his blood stream, hence the healthy person also gets malarial disease.

Viruses differ from other micro-organisms because they are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Hence, viruses differ from other micro-organisms.

Microorganisms such bacteria and fungi that grow on our food items sometimes produce toxic substances. These make the food unfit for consumption. Consuming such food can cause a serious illness called food poisoning.
Food hygiene is essential for preventing food poisoning.

1. Female Anopheles mosquito carries the parasite of malaria.
2. Female Aedes mosquito acts as carrier of dengue virus.

Microorganisms are used for various purposes such as:

• They are used in the preparation of curd, bread and cake.
• They are used in the preparation of alcohol, wine and acetic acid (vinegar).
• They are also used in cleaning up of the environment.
• In agriculture, they are used to increase soil fertility by fixing nitrogen.
• The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Penicillin is an antibiotic made from Penicillium.
• Certain microbes are also used in the biological treatment of sewage and industrial effluents.
• Yeast is used in making idlis, bhaturas, bread, pastries and cakes.

All mosquitoes breed in water. Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc.

Antibiotics are not effective against 'common cold' and 'flu' as these are caused by viruses. And the viruses do not have cells but live in the cells of living beings. And the working mechanism of the antibiotics is to break the cell wall and attack on the bacteria.

1. The fruits which are preserved in the form of pickles by using oil and vinegar as preservative are raw mango and lemon.
2. The fruits which are preserved in the form of jams by using sugar as preservative are mango and orange.

Food preservation: Processing of food to prevent their spoilage and to retain their nutritive value for period is called food preservation.Food can be preserved using following methods:

1. Preservation by Salt.
2. Preservation by Sugar.
3. Preservation by oil and vinegar.
4. Heat and cold treatment.
5. Storage and packing.

Medicines which kill or stop the growth of the disease-causing micro-organisms are called antibiotics. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.Some of the precautions should be taken while taking antibiotics which are as follows:

• Antibiotics should be taken only on the advice of a qualified doctor.
• A person must finish the full course of antibiotics prescribed by the doctor.
• Antibiotics should not be taken unnecessarily.

Yeast is used in baking industry for making bread. It increases the volume of dough. When yeast is mixed in dough for making bread, the yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This makes the dough rise. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

S. No.	Plant Diseases	Mode of transmission
(a)	Rust of wheat	Air, Seeds
(b)	Citrus canker	Air
(c)	Yellow vein mosaic of bhindi (Okra)	Insect

S. No.	Diseases	Causative micro-organisms	Modes of transmission
(i)	Tuberculosis	Bacteria	Air
(ii)	Measles	Virus	Air
(iii)	Chickenpox	Virus	Air/ Contact
(iv)	Polio	Virus	Air/ Water
(v)	Cholera	Bacteria	Water/ Food
(vi)	Typhoid	Bacteria	Water
(vii)	Hepatitis B	Virus	Water
(viii)	Malaria	Protozoa	Mosquito
(ix)	Dengue	Protozoa	Mosquito

S. No.	Diseases	Causative micro-organisms	Modes of transmission
(i)	Tuberculosis	Bacteria	Air
(ii)	Chickenpox	Virus	Air/ Contact
(iii)	Polio	Virus	Air/ Water
(iv)	Cholera	Bacteria	Water/ Food
(v)	Malaria	Protozoa	Mosquito

Some bacteria like rhizobium and blue green algae like Nostoc and Anabaena present in the soil are able to fix nitrogen gas from the atmosphere to enrich soil with nitrogen and increase its fertility. These micro-organisms are commonly called biological nitrogen fixers.

Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Cholera and tuberculosis are examples of communicable diseases.

Some micro-organisms decompose the organic matter of dead plants and animals and convert them into simple substances which mix up with the soil. These substances are again used by other plants and animals. Thus, micro-organisms decompose the harmful and smelly dead remains of plants and animals into harmless materials and thereby clean up the environment.

Milk is turned into curd by bacteria. Milk contains many microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd.When a small amount of pre-made curd is added into warm milk, then lactobacillus bacterium present in curd multiplies in milk and converts it into curd. During this process, lactobacillus bacterium acts on lactose sugar present in milk and converts it into lactic acid. This lactic acid then converts milk into curd.

The communicable diseases can occur and spread in the following ways:

• Through air we breathe.
• Through water we drink.
• Through food we eat.
• Through carriers such as mosquito.