UPSC Prelims 2001 Q128: Science & Technology – Biology
Antigen is a substance which
- (a) destroys harmful bacteria
- (b) is used to treat poisoning
- (c) lowers body temperature
- (d) stimulates formation of antibody
Answer: (d) stimulates formation of antibody
Explanation
What an antigen is
| Term | Meaning |
|---|---|
| Antigen | A foreign substance that stimulates the formation of antibodies |
| Antibody | Protein made by B-cells that binds the antigen |
| Antidote | Substance used to treat poisoning |
| Antipyretic | Drug that lowers body temperature |
An antigen (antibody generator) is any foreign molecule — often a protein on a germ — that the immune system recognises and that stimulates the formation of antibodies. Vaccines work by exposing the body to harmless antigens.
Answer: (d) stimulates formation of antibody.
Why each option is right or wrong
- (a) Incorrect. Destroying bacteria is the work of antibodies and white blood cells.
- (b) Incorrect. A substance that treats poisoning is an antidote.
- (c) Incorrect. A substance that lowers temperature is an antipyretic.
- (d) CORRECT. An antigen stimulates the formation of antibodies.
Key point
Antibodies (immunoglobulins): IgG, IgA, IgM, IgE, IgD; IgG crosses the placenta.
Remember
Antigen stimulates antibody formation.
Common mistakes
- Swapping the meanings of antigen and antibody.
- Thinking an antigen fights bacteria itself.
- Confusing it with an antidote or antibiotic.
Exam tip
Antigen = trigger; antibody = response.
Sources
- NCERT Class XII — Biology, chapter 'Human Health and Disease' (immunity)
- NCERT Class VIII — Science, chapter 'Microorganisms: Friend and Foe' (vaccines)