Microorganisms: Friend and Foe Class 8 Science Important Questions Chapter 2

Ans 1 – (b) yeast

Ans 2 – (b) producers

Ans 3 – (a) Bacillus

Ans 4 – (c) Algae

Ans 5 – (d) malaria

Ans 6 – (d) Penicillin

Ans 7 – (c) A virus

Ans 8 – (a) anopheles mosquito

Ans 9 – (b) fermentation

Ans 10 – (c) 70°C

Ans 11 – (c) Rhizobium

Ans 12 – (a) water

Ans 13 – (c) virus

Ans 14 – (c) streptomycin

Ans 15 – (a) bacterium

Ans 16 – (d) bacterium

Ans 17 – (c) cholera

Ans 18 – (b) paramecium

Ans 19 – (a) lactobacillus

Ans 20 – (a) plant proteins

Ans 21 – (b) blue-green algae

Ans 22 – (a) bacteria

Ans 23 – (a) bacteria

Ans 24 –  

Ans 25 – Air

Ans 26 – Female Aedes

Ans 27 – Nitrogen

Ans 28 –

(a) Bacteria

(b) Algae

(c) Fungi

(d) Protozoa

(e) Viruses

Ans 29 –

Ans 30 – Chlamydomonas and diatoms are single-celled algae.

Blue-green algae and Spirogyra are multicellular algae.

Ans 31 – The history of smallpox holds a unique place in medicine. It was one of the deadliest diseases known to humans, and to date (2016) the only human disease to have been eradicated by vaccination. The smallpox vaccine, introduced by Edward Jenner in 1796, was the first successful vaccine to be developed. He observed that milkmaids who previously had caught cowpox did not catch smallpox and showed that inoculated vaccine protected against inoculated variola virus.

Ans 32 – The insect (or other animal) which transmits disease-causing micro-organisms to humans (without itself suffering from them) is called a ‘carrier’.

The most common carriers of disease-causing micro-organisms (or microbes) are:

• Housefly
• Mosquito

Ans 33 – (a) Algae – Spirogyra, Chlamydomonas
(b) Fungi – Aspergillus, yeast
(c) Protozoa – Paramecium, Amoeba

Ans 34 – The microorganisms cannot be seen with naked eyes because they are very small in size. Some of these, such as fungus growing on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes.

Ans 35 –

1. Viruses are also microscopic but are different from other microorganisms.

2. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
3. Some of the viruses are Common ailments like cold, influenza (flu) and most coughs are
caused by viruses.
4. Serious diseases like polio and chicken pox are also caused by viruses.
5. Diseases like dysentery and malaria are caused by protozoa (protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.

Ans 36 –

1. Bacteria: Causes various diseases such as typhoid, diarrhea, and cholera.
2. Fungi: Causes a large number of diseases in plants and in animals such as rust diseases in plants, fruit rot in apple, red rot in sugar cane and ring worm disease in human beings.
3. Algae: Algal boom in water (rapid growth of algae) causes poisonous effect after they die, which in turn results in the death of aquatic organisms.
4. Protozoa: Causes Amoebic dysentery, pyorrhoea and sleeping sickness etc.
5. Virus: Cause small fox, common cold, influenza, herpes, hepatitis, polio and rabies.

Ans 37 –  Antibiotics are the chemicals which inhibit the growth of pathogenic microorganisms in our body thus helps us to control and cure diseases like, typhoid, diphtheria, pneumonia and tuberculosis. The precautions are :-

1) We should not take dose of antibiotics.

2) Antibiotics should not be taken empty stomach.

3) We should complete the dose of antibiotic as advised by the doctor.

4) We should take antibiotic only after consulting a doctor.

Ans 38 –  Yeast is used for the leavening of bread. Yeast uses the sugars and oxygen in dough to produce more yeast cells and carbon dioxide gas. Yeast uses sugars by breaking them down into carbon dioxide and water. The yeast needs lots of oxygen in order to complete this type of fermentation.
Baker’s yeast is the common name for the strains of yeast commonly used in baking bread and bakery products, serving as a leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentable sugars present in the dough into carbon dioxide and ethanol.

Ans 39 – Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, or other physical contacts; e.g., cholera, chicken pox, tuberculosis, common cold, etc.