CBSE Class 8 Answered

3.

Food preservation is the process of treating and handling food in order to stop or slow down its spoilage while maintaining its nutritional value, texture and flavour.

Methods of food preservation:

• Salting
  • Biodegradation is prevented under normal conditions
  • Preserved food materials: Fish, pickles
• Preservation by sugar
  • Reduces the moisture content which inhibits the growth of bacteria
  • Preserved food materials: Jams, jellies, squashes
• Dehydration (Drying)
  • Inhibits growth of microbes
  • Preserved food materials: Grains, meat, fish, vegetables
• Irradiation
  • Radioactive or ultraviolet radiation kills microorganisms
  • Preserved food materials: Bakery products
• Pasteurisation
  • Heating to temperature of about 60°C for 30 min and then chilling kills bacteria
  • Preserved food materials: Milk

4. Pasteurisation involves heating to temperature of about 60°C for 30 min and then chilling which kills the bacteria present in food.

• Preserved food materials: Milk

5. Role of microorganisms in cleaning the environment:

• Microorganisms break down or decompose complex organic matter such as wastes of vegetables, fruits, plants and animals, and convert them into simple substances, thereby cleaning the environment.
• Some algae are used in space flights to purify the air in spaceships.
• Some kinds of bacteria are able to decompose oil and thus help in cleaning oil sludge from oil tankers in the sea.