Science Question Answer (2 Marks)

We preserve cooked food in the refrigerator at home. Low temperature inhibits the growth of micro-organisms. When cooked food is kept in a cold place, then the food does not get spoiled easily.

The full form of HIV is Human Immunodeficiency Virus. HIV causes AIDS disease.

Some bacteria and blue green algae present in the soil and rhizobium present in the root nodules of leguminous plants can fix atmospheric nitrogen.

The following diseases are caused by the micro-organisms:

Animal Diseases	Plant Diseases
Anthrax	Citrus Canker
Foot and mouth	Rust of Vein

1. Yellow vein mosaic of bhindi (Okra).
2. Citrus canker.
3. Rust of wheat.

The houseflies feed on garbage, animal excreta and dead organic matter. When the housefly sits on garbage and animal excreta for feeding, then the millions of disease-causing micro-organisms present in them sticking to the body of housefly. And when this housefly sits on uncovered food, they may transfer the pathogens and food gets contaminated. When this contaminated food is consumed by a person, pathogens enter into his body and causes various diseases.

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

1. Food should always be kept covered.
2. Proper sanitation should be maintained in the kitchen.

The process of conversation of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation in 1857.

Sodium benzoate and sodium meta bisulphite are common preservatives which are used in the preservation of fruits as jams and jellies.

Rhizobium bacterium is found in the soil. It lives in the root nodules of leguminous plants such as beans and peas, with which it has a symbiotic relationship. It is involved in the fixation of nitrogen in leguminous plants (pulses).

The process of pasteurization for the preservation of milk is discovered by Louis Pasteur. In this process, milk is heated to about 700C for 15 to 30 seconds to kill bacteria. Next it is chilled very fast to prevent bacteria from growing. It is finally stored at low temperature. This Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Preservation by deep freezing means preservation of food material in the extreme cold. Low temperature inhibits the growth of micro-organisms completely. Food materials such meat and fish are usually preserved by deep freezing.

Yeast converts sugar into alcohol during fermentation. Yeast is used for commercial production of alcohol and wine.

1. The plant disease, Rust of wheat is caused by fungi.
2. Yellow vein Virus Insect mosaic of bhindi (Okra), a plant disease, is caused by virus.
3. Citrus canker is caused by bacteria.

Salt, oil and vinegar are some of the preservatives which are used in the preservation of fruits and vegetables as pickles.

Micro-organisms are too much smaller that they cannot be seen with naked eye. They can be seen with a magnifying glass called microscope.

1. Bacteria: (I) Lactobacillus bacteria (II) Rhizobium bacteria.
2. Viruses: (I) HIV (II) Tobacco Mosaic virus (TMV).
3. Protozoa: (I) Amoeba (II) Paramecium.
4. Algae: (I) Spirogyra (II) Chlamydomonas.
5. Fungi: (I) Penicillium (II) Aspergillus.

The organisms which are too small to be seen by the naked eyes and can be seen only though a microscope are called micro-organisms or microbes. Bacteria and viruses are examples of micro-organisms.