Under unfavourable conditions of temperature and water, they generally form a hard and tough covering called cyst. This protects them. When favourable conditions come, they emerge from their shell, multiply and go through their life cycle.

Alexander Fleming discovered first antibiotic penicillin. Two other common antibiotics are streptomycin and tetracycline.

Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.

Fermentation is the process by which yeast converts sugars into alcohol.

The body produce antibodies when a disease carrying microbe enters in it. The body also retains memory of this encounter to fight the microbe if it enters again. A vaccine consists of dead or weakened microbes which when introduced in a healthy body, produce suitable antibodies to fight and kill themselves. These antibodies remain in the body to protect it from disease causing microbes thus develop immunity.

The milk is heated to 70°C for 15 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called Pasteurization.

The milk that comes in packets does not get spoiled because it is pasteurised. Pasteurised milk can be consumed without boiling as it is free from harmful microbes. The milk was heated to about 70⁰ C for 15-30 second and then cooled suddenly and finally packed. By doing so, the growth of microbes was prevented. This process is called pasteurisation.

The ideal conditions for bacteria to multiply are moisture, food and warmth. (b) is kept under cold temperature which prevents decomposing. (c) and (d) are under normal temperature but not as moist as (a). So, only (a) has the most suitable conditions for bacteria to multiply.

Bacteria are too small, cannot be seen with the naked eye. It can be seen only with a microscope.That's why Ankur could not see the bacteria on his hands. Bacteria can cause various diseases like dysentry, typhoid, cholera, etc.

Useful micro-organisms:
(i) Friendly micro-organisms: They are used for various purposes. They are used in making curd (Lactobacillus bacteria) and bread. They are ingredients of Idli, Dhoklas and Bhaturas.
(ii) Commercial uses: Micro-organisms are used for the large scale production of alcohol and wine. Yeast is grown on natural sugars present in grains such as barley, wheat, rice, fruit juices for this purpose.
(iii) Medicinal uses: A very useful medicine group 'antibiotics' is prepared from micro-organisms. Commonly-used antibiotics are formed by fungi and bacteria. Vaccine also protects us from microbes.
(iv) Increasing soil fertility: Some bacteria and bluegreen algae are able to fixnitrogen from atmosphere and form nitrogen compounds which increase the soil fertility.
(v) Decomposers: They decompose the dead organic substances into their constituents and clean the environment.

(a) Microorganism is bread mould (Rhizopus) and the group is fungi.
(b) Organism grows on moist and stale bread.
(c) It grows well in moist condition.
(d) No, the fungus spoils the bread by producing poisonous substances (toxins).

(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.