5. Explain the uses and the harmful effects of micro-organisms.

Ans: 

Uses of micro-organisms:

(i) Microorganisms present in the soil, dung, etc. decompose the garbage and convert it into manure.

(ii) Some microorganisms present in the soil and those in the root nodules of leguminous plants convert atmospheric nitrogen into its compounds.

(iii) Microorganisms are also useful in the fermentation process and in the production of milk products like butter, buttermilk, cheese, paneer, etc.

(iv) They are used for the production of antibiotics, vaccines, tanning of skin, and ropes and strings from agave.

e.g., some microbes are used to clear a layer of oil floating on the surface of an ocean or lake.

Harmful effects of micro-organisms:

(i) As microbes use foodstuffs for their own nutrition, some microbes release toxic materials (enterotoxins) into the food. Such toxins spoil the food.

(ii) Eating spoiled food can cause loose motions and vomiting (food poisoning).

(iii) If contaminated food or water is consumed, an individual may suffer from amoebiasis, typhoid, cholera, hepatitis, gastroenteritis, etc.

(iv) If a person breathes air contaminated with various disease-causing microbes, he or she will suffer from diseases like the common cold, cough, diphtheria, pneumonia, tuberculosis, etc.

e.g., certain microbes cause diseases like malaria, dengue, elephantiasis, yellow fever, etc.

6. Give reasons.

(a) Diseases spread on a large scale during periods of heavy rainfall and floods.

Ans: 

(i) Heavy rainfall followed by flooding creates favourable conditions for the growth and spread of various disease-causing bacteria.

(ii) Heavy rainfall may also cause the spread of water contaminated with pathogenic microbes in places that lack proper sanitation facilities.

Therefore, diseases spread on a large scale during periods of heavy rainfall and flooding.

(b) There is a possibility of food poisoning if we eat stale food.

Ans: 

(i) If food is kept open for a longer duration, some microorganisms may grow on it and release toxic materials (enterotoxins) into it.

(ii) Fungus grows quickly on moist and stale food. Therefore, there is a possibility of food poisoning if we eat stale food.

(c) Soil is turned over during tilling.

Ans: 

(i) Tilling is an agricultural procedure that involves the mechanical agitation of soil by various means, such as digging, stirring, and overturning.

(ii) The soil contains both bacteria and fungi, which help in the decomposition of organic matter.

(iii) More intensively tilled soil tends to have high nutrient availability and enhanced nutrient levels.

Therefore, soil is turned over during tilling.

(d) Fungus grows quickly in moist or humid conditions.

Ans: 

(i) Fungi need moist or damp areas to grow and reproduce.

(ii) High humidity favours the growth of fungi. Therefore, fungus grows quickly in moist or humid conditions.

(e) A refrigerator is used in almost every home.

Ans: 

(i) A refrigerator maintains a temperature of 0°C to 4°C.

(ii) Microorganisms grow within a specific range of temperatures, i.e., from 25 °C to 37 °C.

(iii) To avoid the growth of microorganisms and the spoilage of food materials, refrigerators are used. 

Therefore, a refrigerator is used in almost every home.

(f) Bread ‘rises’ during baking.

Ans:

(i) Specific useful microorganisms like yeast are used in the bread-making process.

(ii) These microorganisms carry out fermentation.

(iii) Carbon dioxide and some other gases are released in this process.

(iv) These gases cause an increase in volume. Therefore, bread ‘rises’.

(g) Fodder is soaked in water before offering to cattle.

Ans:

(i) Soaking of fodder causes sprouting of grains.

(ii) Sprouting fodder produces a grainy grass that is high in protein and energy.

(iii) This is an ideal combination to create a healthy and strong animal.

Hence, fodder is soaked in water before being offered to cattle.

7. When will you use a simple microscope and when, a compound microscope? Explain in detail how you will use them.

Ans: 

(i) A microscope is an optical instrument that is used to see highly magnified images of tiny objects.

(ii) It is used to see objects that are smaller than 100 micrometres in size and cannot be seen with our naked eyes.

(iii) The simple microscope is used for enlarging small objects that are visible to the eyes.

(iv) The compound microscope is used for observing cells or objects that are smaller than 100 micrometres.

(v) An entire organism or structure, small enough or thin enough, is placed directly on a microscope slide (example: a small unicellular or multicellular organism) and observed under a microscope.

(vi) To observe blood cells or cells suspended in fluid, the sample is thinly spread on a slide and observed under a microscope.