BIOLOGY [3 marks Question Answer]

Food stuffs may be protected from the attack of fungi and bacteria by the following ways.

• Dry the food, this prevents microorganisms to multiply. Cereals and pulses are dried under the sun before storage.
• Fungicides can be sprayed on standing crops from being destroyed.
• Keep the food at low temperature in the refrigerator prevents spoilage of food. As fungus does not multiply in cold conditions.
• Using of salt, sugar or other chemical preservatives prevents the growth of fungus.

Bacteria are useful on the commercial basis
There uses are :

• They are used in the manufacture of vinegar, curd and cheese.
• They are also used in the production of tea coffee and cocoa.
• Lactic acid, citric acid and alcohol are also obtained by the action of bacteria.
• Bacteria are also involved in tanning of leather.
• Retting of fibres is also brought about by the action of bacteria.
• Bacteria also help in generating biogas.
• Certain medicines like antibiotics and vitamin B complex are manufactured with the help of bacteria

Algae are useful in the following ways :

• They are the major sources of food for organisms that cannot make their own food and live in water.
• They also release and large amount of oxygen during photosynthesis.
• Algin, used for preparing ice- cream and toothpaste is obtained from kelp, an. alga.
• Agar obtained from red algae is used in the laboratory for various experiments.
• Some red algae are also used as food since they are a rich source of proteins, vitamins and minerals.
• The cell wall of diatoms contains silica and are extensively used in making metal polish, toothpaste and porcelain.

Conditions which facilitate the growth of bacteria are :
a. Most bacteria grow best in the range of temperature between 25°C to 40°C. Some bacteria can grow at a very high or low temperature.
b. Bacteria grow best in darkness. Sunlight kills many kinds of bacteria. 
c. They become active in moisture otherwise become inactive.
d. Most of the bacteria can survive under extreme harsh conditions due to formation of hard protective covering around them called a cyst or a spore. They remain inactive in the cyst during unfavourable conditions.
e. They are also affected by the presence or absence of oxygen.