Gas Exchange Mechanisms Across Animals — NEET Biology
✅ Asked in NEET 2026Mechanisms of breathing vary among different groups of animals depending mainly on their habitats and levels of organisation. Lower invertebrates like sponges, coelenterates, flatworms, etc., exchange O₂ with CO₂ by simple diffusion over their entire body surface. Earthworms use their moist cuticle and insects have a network of tubes (tracheal tubes) to transport atmospheric air within the body. Special vascularised structures called gills (branchial respiration) are used by most of the aquatic arthropods and molluscs whereas vascularised bags called lungs (pulmonary respiration) are used by the terrestrial forms for the exchange of gases. Among vertebrates, fishes use gills whereas amphibians, reptiles, birds and mammals respire through lungs. Amphibians like frogs can respire through their moist skin (cutaneous respiration) also.
NTA tests students' ability to match respiratory structures with animal groups. Since the 2026 NEET paper asked about amoeba (a protist using simple diffusion), students must recognize that lower organisms like amoeba, sponges, and flatworms lack specialized respiratory organs and rely entirely on diffusion across their body surface. The common mistake is assuming all animals need specialized structures like gills or lungs—actually, organisms with small size or high surface-area-to-volume ratios exchange gases directly through their skin. Remember: lower invertebrates = diffusion; aquatic arthropods/molluscs = gills; terrestrial vertebrates = lungs; amphibians = both lungs AND skin respiration.
Match List I with List II — A. Molluscs, B. Reptiles, C. Adult amphibians, D. Amoeba.
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