Uses of Bacteria:
(i) They are used to increase soil fertility by fixing nitrogen.
(ii) Some bacteria are used to produce antibiotics.
(iii) Lactobacillus bacterium converts milk into curd.
(iv) Some bacteria help in many functions of our body.
Uses of Fungi:
(i) Yeasts are used to prepare alcohol and vinegar by fermentation.
(ii) Mushrooms are eaten as food.
(iii) Penicillin is an antibiotic formed by a fungus called Penicillium.
Uses of Algae:
(i) Algae are used to make jellies.
(ii) Chlorella is used to obtain proteins.
(iii) Silicafrom diatoms are used in toothpastes.

The chemical substances which are used to check or stop the growth of harmful micro-organisms in food are called food preservatives. These food preservatives keep the edible food materials protected from the invasion of micro-organisms which can spoil the food. Some common food preservatives are :
(i) Salt: Common salt is used to preserve meat, fish, amla raw mangoes, tamarind, etc.
(ii) Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria, that can spoil food.
(iii) Oil: Edible oils are used as preservatives in vegetables and pickles. Oil does not allow the moisture to surface, thus preventing the growth of harmful bacteria.
(iv) Vinegar: It is used to preserve fruits, vegetables, fish, meat and pickles.

Micro-organisms spoil our food. The process of keeping our food safe from micro-organisms is called food preservation. Various methods of food preservation are :
(i) Drying: It reduces the moisture of food material which prevents growth of micro-organisms. 
(ii) By common salt and sugar: Meat and fish are covered with dry salt to check the growth of bacteria. Sugar reduces the moisture content, which inhibits the growth of bacteria that spoil food.
(iii) By oil and vinegar: Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment.
(iv) Refrigeration and freezing: Low temperature retards the growth of microbes. Thus, it is safe for food.
(v) By chemicals: Chemicals such as sodium benzoate and potassium metabisulphite are used in jams, squash and ketchup.

Micro-organisms are" also very harmful to us. They cause a number of diseases in humans as well as in other animals. Common cold, Tuberculosis, Measles, chicken pox, polio, cholera, typhoid, hepatitis-B. malaria are some common human diseases caused by micro-organisms. Anthrax is a serious disease in animals caused by microbes. They also make food items unfit for use by food poisoning. They also spoil clothes and leather products. They also cause diseases in plants like blights in potatoes, sugarcane, oranges, etc. They also reduce the crop production.

(a) Organisms that cannot be seen with eyes alone are called microbes.
(b) Microbes are useful to humans in many ways. They help in the production of curd, cheese, in cleaning the environment, etc.
(c) (i) Lactobacillus bacteria.
(ii) Penicillium
(d) Diseases caused by microbes are polio, malaria, etc.
(e) Jasmine is attentive, intelligent and curious.

(a) Cholera By maintaining personal hygiene and good sanitation practices.
(b) Typhoid Eating properly cooked food, drinking boiled water and by getting vaccinated against the disease.
(c) Hepatitis-A Drinking boiled water and getting vaccinated against the disease

Virus:

Amoeba: