Refrigerators and freezers use insulation and cooling agents like ammonia to keep temperatures below freezing. This allows food to be preserved for long periods by freezing it quickly to form small ice crystals that don't damage cell structures. Thermostats regulate temperatures to keep food safely frozen or refrigerated.

1. Refrigeration and Refrigerators

2. Proportion : the relation of one part to another or to the whole. example: WORD STUDY: There is a high proportion of nitrogen in the atmosphere.

3. Burst : break open by force. example: You can burst a car tyre by sticking a nail in it.

4. Essential : vital, very important. example: Proteins and vitamins are essential to good health.

5. Insulated : encased in a poor conductor material.

6. An insulated container is encased in a material that is a poor conductor of heat, so that the temperature inside remains unaffected by the temperature outside.

7. Blasting : blowing very hard with high-pressure air.

8. example: Food can be frozen by placing it in an insulated container and blasting it at high speed with air cooled below -30 ° C.

9. Vegetables and meat can be preserved in brine . brine : salt water. example:

10. freezer : It is a refrigerator which keeps its contents at temperatures well below freezing point. example: Freezer A freezer is a type of refrigerator which we use for long storage.

11. thawed out : unfrozen examples: Frozen food is thawed out simply by raising its temperature over O°C. When snow thaws , it melts.

12. poultry : domestic birds such as hens, ducks, geese and turkeys. examples: Poultry can usually be eaten. Poultry is a collective word which is uncountable and has no plural.

13. cooling agent : a substance which cools other substances. examples: An agent is the active substance in a process. Certain chemicals are used as drying agents .

14. cycle: a continuing process in which certain actions and reactions are repeated over and over again, e.g. the water cycle.

16. thermostat : an instrument which maintains a constant temperature.

17. A thermostat usually consists of a bimetallic strip and two contact points , one to a heater and one to a cooler . The heater is switched on when the temperature falls below the required level and the cooler is activated when the temperature rises above the required level. Brass and iron are the two metals usually used.

18. QUESTIONS ON THE TEXT Answer these questions: How do sub-zero temperatures affect harmful micro-organisms? Micro-organisms cannot grow or multiply at sub-zero temperatures .

19. b. What does most food consist of? Most food consists of animal or plant cells containing a high proportion of water.

20. c) Why is food spoilt if it is frozen gradually? Food is spoilt because the water expands and forms large crystals of ice which burst the cell membranes and destroy the structure of food.

21. d) What do the stars on a refrigerator indicate? The stars on a refrigerator indicate the minimum temperature the refrigerators can reach.

22. e- Which property of ammonia makes it a suitable cooling agent? Ammonia condenses and re-evaporates quickly when the pressure on it varies.

23. f. What would happen if the temperature in a refrigerator rose too high? If the temperature in a refrigerator rose too high, a thermostat would switch off the refrigerator.

24. The faster food is frozen, the smaller the ice crystals formed. The freezing point of brine is lower than that of water. If you have a freezer you can pick strawberries in summer and eat them in mid-winter. Certain gases such as ammonia can be used as a cooling agent in a refrigerator. True and False Statements: