Vidaara.orgClass 12 · Mathematics
CodeVID-M12-WS
Microbes in Human Welfare — Practice Worksheet
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Choose the correct option (A, B, C or D) for each question.
- The answer key is at the end — try the paper first!
Section A — Multiple Choice (1 mark each)
15 × 1 = 15 marks
1.
Most microbes are:
- A.Always harmful
- B.Harmless or useful
- C.Never useful
- D.Plants
2.
Curd is made from milk by:
- A.Lactic acid bacteria
- B.Yeast
- C.Viruses
- D.Algae
3.
Bread dough rises because yeast produces:
- A.Oxygen
- B.Carbon dioxide
- C.Nitrogen
- D.Water only
4.
Alcohol and beverages are produced by yeast through:
- A.Fermentation
- B.Photosynthesis
- C.Respiration in light
- D.Digestion
5.
The first antibiotic, penicillin, was discovered by:
- A.Mendel
- B.Alexander Fleming
- C.Darwin
- D.Watson
6.
Antibiotics are medicines that:
- A.Kill or stop bacteria
- B.Make food rise
- C.Fix nitrogen
- D.Produce biogas
7.
In sewage treatment, organic matter is broken down by:
- A.Microbes
- B.Salt
- C.Boiling
- D.Freezing
8.
The main gas in biogas is:
- A.Oxygen
- B.Methane
- C.Nitrogen
- D.Carbon dioxide
9.
Microbes that produce biogas are called:
- A.Methanogens
- B.Carcinogens
- C.Pathogens
- D.Antigens
10.
Cattle dung is used to start a biogas plant because it contains:
- A.Methanogen microbes
- B.Penicillin
- C.Antibodies
- D.Vitamins only
11.
Living microbes that enrich the soil with nutrients are:
- A.Biofertilisers
- B.Pesticides
- C.Antibiotics
- D.Vaccines
12.
Rhizobium enriches soil by:
- A.Fixing nitrogen
- B.Killing insects
- C.Making curd
- D.Producing alcohol
13.
A fungus that partners with roots to help absorb phosphorus is:
- A.Mycorrhiza
- B.Yeast
- C.Penicillium
- D.Anabaena
14.
Controlling pests using living organisms instead of chemicals is:
- A.Biocontrol
- B.Fermentation
- C.Vaccination
- D.Metastasis
15.
Bacillus thuringiensis (Bt) is used to kill:
- A.Certain insect larvae
- B.All plants
- C.Useful bacteria
- D.Humans
Section B — Challenge / Olympiad (2 marks each)
6 × 2 = 12 marks
16.
Curd is more nutritious than milk partly because lactic acid bacteria:
- A.Add vitamins and improve nutrition
- B.Remove all nutrients
- C.Add antibiotics
- D.Make it sterile
17.
Releasing untreated sewage into a river is harmful because the organic matter lets microbes multiply and:
- A.Use up the water's oxygen, harming fish
- B.Add oxygen
- C.Purify it instantly
- D.Make biogas in the river
18.
Biogas plants are especially valuable in villages because they turn cattle dung into:
- A.Clean cooking fuel and useful manure
- B.Antibiotics
- C.Curd
- D.Drinking water
19.
Biofertilisers are preferred over chemical fertilisers because they:
- A.Enrich soil without polluting it
- B.Cost the most
- C.Kill all crops
- D.Add carcinogens
20.
Using ladybird beetles to control aphids is an example of biocontrol because it relies on a:
- A.Natural predator instead of a chemical pesticide
- B.Stronger poison
- C.New antibiotic
- D.Vaccine
21.
Bt is considered safer than chemical insecticides mainly because it:
- A.Targets specific insect larvae and spares other animals
- B.Kills everything it touches
- C.Pollutes water heavily
- D.Cannot kill any insect
Answer Key
Section A — Multiple Choice (1 mark each)
- (B) Harmless or useful
- (A) Lactic acid bacteria
- (B) Carbon dioxide
- (A) Fermentation
- (B) Alexander Fleming
- (A) Kill or stop bacteria
- (A) Microbes
- (B) Methane
- (A) Methanogens
- (A) Methanogen microbes
- (A) Biofertilisers
- (A) Fixing nitrogen
- (A) Mycorrhiza
- (A) Biocontrol
- (A) Certain insect larvae
Section B — Challenge / Olympiad (2 marks each)
- (A) Add vitamins and improve nutrition
- (A) Use up the water's oxygen, harming fish
- (A) Clean cooking fuel and useful manure
- (A) Enrich soil without polluting it
- (A) Natural predator instead of a chemical pesticide
- (A) Targets specific insect larvae and spares other animals
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