Which animal group breathes through what? Cockroach tracheae and frog skin keep confusing me
Yash Tiwari11th Sample
8 Sept 2026 · 1 min read
bhai Breathing and Exchange of Gases ka first topic hai aur already confusion. NCERT ka line hai "the mechanism of breathing varies among different groups of animals depending mainly on their habitats and levels of organisation".
Meri list:
- Sponges, coelenterates, flatworms: simple diffusion over body surface (I think)
- Earthworms: moist cuticle
- Insects: network of tubes (tracheal system)
- Aquatic arthropods and molluscs: gills
- Fishes: gills
- Reptiles, birds, mammals: lungs
- Amphibians: lungs but also skin??
Doubts:
- Insects have a tracheal system. Does blood carry oxygen in insects like it does in us? Test mein option aaya tha "blood transports oxygen in cockroach" and I marked it true.
- Frog: agar lungs hain toh skin kyun? Does the skin do real respiration or just a little?
- Earthworm ka "moist cuticle" and frog ka "moist skin": why does it need to be moist?
If someone has a mnemonic I'd be very happy bhai, mera yaadasht weak hai 😅
6 answers & replies
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[+][–]Diya Menon11thSample· 1mo ago
your list is already almost perfect yash, ahh! One more small thing: amphibians like frogs can respire both through lungs and through moist skin (cutaneous respiration), so you were right with the double thing. All the other pairs are exactly as in NCERT. The simplest ones, sponges, coelenterates and flatworms, have no special organ, they exchange gases by simple diffusion over their body surface.
[+][–]Sara Fernandes11thSample· 1mo ago
about insects: I think blood carries the oxygen in cockroaches too, because all animals with a circulatory system do it that way? So the option is true, just the tracheae make the first step.
[+][–]Nisha Verma12thSample· 1mo ago
Sara, in insects the tracheal system is the whole transport system for oxygen. The body has openings called spiracles, which lead to a network of tracheal tubes that branch into very fine tracheoles. Air goes directly to the tissues and cells, so blood (haemolymph) doesn't need to carry O2 for respiration. That's why your test option should have been false. NEET likes this trap: "insects have an open circulatory system but the tracheal tubes carry the oxygen".
[+][–]Yash Tiwari11thSample· 1mo agoAuthor
oh wait, so insects don't use blood for O2 at all, tubes se direct cell tak. okay got it bhai, marking that option false in my notes. thanks Nisha didi!
[+][–]Rahul DubeyDropperSample· 1mo ago
Why moist: gases can only diffuse across a surface if they are dissolved in a thin film of water. O2 dissolves in the moisture on the skin and then diffuses into the blood vessels below; CO2 diffuses out the same way. A dry skin or a dry cuticle is a barrier to gas exchange. That's why earthworms stay in damp soil and come out in rains, and why they die if they are left in the sun to dry. Frogs also keep their skin moist with mucus and water.
For your 2nd doubt: yes, frog skin is a real respiratory surface, which is useful when it is in water or at rest.
[+][–]Siddharth RaoDropperSample· 1mo ago
Mnemonic to put the NCERT list in a story: "Simple things (sponge, coelenterate, flatworm) breathe through the skin; Worms need wet skin; Insects have Tubes; Molluscs and aquatic arthropods have Gills; Fish too; Frogs do both; and Reptiles-Birds-Mammals use Lungs". Say it with the animals in order, from simple to complex, and it follows evolutionary complexity, which also helps you remember why lungs appear last.
