CG Board Class 8 Science Chapter 8 Solutions: Micro-organisms – A Wonderful World (सूक्ष्मजीव – एक अद्भुत संसार) – 2026-27

(1) How does boot polish protect leather shoes?**

Boot polish creates a smooth, wax-coated water-resistant layer over leather shoes. This layer keeps moisture out, preventing fungal spores from germinating and spoiling the leather.

• (2) Why does curd sometimes turn bitter?

Leaving curd at warm temperatures for too long causes excessive multiplication of Lactobacillus and wild bacteria, producing excess lactic acid and protein decomposition products that make it bitter.

• (3) Why must the milk be lukewarm when curd is to be made from it?

Lukewarm milk (around 37 deg C) provides the optimum temperature required for Lactobacillus bacteria to grow fast and set curd. Extremely cold or boiling milk prevents bacterial growth.

• (4) How does the leguminous plants increase the fertility of the soil?

Symbiotic Rhizobium bacteria residing in the root nodules of leguminous plants fix atmospheric nitrogen gas into soluble nitrates in the soil, enhancing soil fertility.

• (5) Why must we safeguard food items from micro-organisms?

Micro-organisms spoil food by decomposing it and producing toxic by-products, which cause food poisoning, vomiting, diarrhea, and diseases.

• (6) What are the mediums through which micro-organisms enter our body?

Pathogens enter our body through

1. Contaminated food and drinking water
2. Inhaled air containing cough droplets
3. Vector bites like mosquitoes and flies
4. Direct physical contact, infected blood, or skin wounds

• (7) Must we use the handkerchief used by a person suffering from cold and fever or not? Explain with reasons.

No, we must not use it because respiratory viruses and bacteria contaminate the handkerchief. Using it transfers viruses directly to our hands and respiratory passages, leading to infection.

• (8) What happens, when our body loses its resistance power?

When disease resistance drops, white blood cells fail to destroy pathogens. Micro-organisms multiply rapidly, causing disease symptoms like fever, weakness, and recurring infections.

• (9) Why is cleanliness necessary for being healthy?

Hygiene prevents the growth and spread of disease-causing bacteria, viruses, fungi, and insect vectors, keeping our body and surroundings free of infections.

• (10) What will happen if a small amount of curd is added to milk to prepare curd and then heated?

High heat kills the beneficial Lactobacillus bacteria present in the curd starter, preventing fermentation and failing to set the curd.

• (11) Why do the doctors advise us to drink boiled water?

Boiling kills all harmful disease-causing micro-organisms (bacteria, protozoa, viruses) present in water, protecting us from waterborne diseases like cholera and dysentery.

(1) With the help of your teachers, relatives, newspapers and magazines try to make a list of beneficial and harmful processes caused by micro-organisms.**

• Beneficial Processes:

1. Formation of curd, butter, and cheese from milk using Lactobacillus bacteria.
2. Fermentation of dough for bread, idli, dosa, and jalebi using Yeast.
3. Atmospheric nitrogen fixation by Rhizobium in legume roots.
4. Decomposition of dead organic matter into fertile manure.
5. Industrial manufacture of antibiotics, vaccines, alcohol, and vinegar.

• Harmful Processes:

1. Causing diseases in humans (e.g., cholera, tuberculosis, polio, malaria, AIDS).
2. Food spoilage and rotting of fruits, vegetables, and milk.
3. Destruction of leather, wood, and clothes by fungal decay.
4. Crop diseases in agriculture (e.g., Irish potato blight).