UPSC Prelims 2007 Q114: Science & Technology – Biology
How do most insects respire?
- (a) Through skin
- (b) Through gills
- (c) By lungs
- (d) By tracheal system
Answer: (d) By tracheal system
Explanation
How insects breathe — the tracheal system
| Part | Job |
|---|---|
| Spiracles | Small openings on the body sides |
| Tracheae | Air tubes branching through the body |
| Tracheoles | Finest tubes — deliver oxygen directly to cells |
Insects do not use blood to carry oxygen the way we do.
Air goes straight to the tissues through the tubes.
Breathing organs in animals:
| Animal | Organ |
|---|---|
| Insects (cockroach, grasshopper) | Tracheae |
| Earthworm | Skin (moist) |
| Fish | Gills |
| Frog | Skin + lungs (+ buccal lining) |
| Mammals, birds | Lungs |
Answer: (d) By tracheal system.
Why each option is right or wrong
- (a) Incorrect. Skin breathing is seen in earthworms and frogs.
- (b) Incorrect. Gills are used by fish and some aquatic larvae.
- (c) Incorrect. Lungs belong to vertebrates like mammals and birds.
- (d) CORRECT. Most insects breathe through spiracles and tracheae.
Key point
Insects: spiracles → tracheae → tracheoles → cells. Earthworm: skin. Fish: gills. Mammals: lungs.
Remember
Most insects breathe through a tracheal system.
Common mistakes
- Thinking insects breathe with lungs; they use a network of tracheal tubes.
- Confusing the tracheal system of insects with the human trachea (windpipe).
- Forgetting that in insects, blood (haemolymph) does not carry oxygen.
Exam tip
Insects breathe through 'holes in the sides' (spiracles). That is why tracheal size limits how big insects can grow.
Sources
- NCERT Class VII — Science, Ch 10 (Respiration in Organisms)
- NCERT Class XI — Biology, Ch 17 (Breathing and Exchange of Gases)