V
Unit V — Amphibia, Reptilia, Aves (Advanced Study Guide)
Concise theory, diagrams, comparisons and exam tips — formatted for printing and revision
1. Amphibia
General characteristics
- First tetrapods: Four‑limbed vertebrates adapted to both aquatic and terrestrial environments.
- Ectothermic: Body temperature largely depends on environment.
- Skin: Moist, glandular, generally without scales — allows cutaneous respiration.
- Respiration: Larvae use gills; adults use lungs and skin (cutaneous).
- Heart: 3‑chambered (2 atria + 1 ventricle).
- Reproduction: Mostly external fertilization in water; eggs are non‑shell membranes (jelly‑coated).
- Development: Indirect life cycle (tadpole → metamorphosis → adult).
Examples
Frog (Rana), Toad (Bufo), Salamander, Caecilian.
Special topic — Parental care
Amphibians show a variety of parental strategies: foam nests, carrying eggs on the back, brooding in the buccal cavity, guarding of eggs. These strategies improve offspring survival in variable environments.
2. Reptilia
General characteristics
- True land vertebrates: Cleidoic (shelled) eggs — independent of water for embryonic development.
- Skin: Dry, keratinized scales that reduce water loss.
- Respiration: Lungs only (no cutaneous respiration).
- Heart: Typically 3‑chambered with partial ventricular septum; crocodiles have a 4‑chambered heart.
- Reproduction: Internal fertilization; most oviparous.
- Excretion: Uricotelic (excrete uric acid) — water‑conserving.
Important orders (examples)
- Chelonia: Turtles, tortoises.
- Crocodilia: Crocodiles, alligators, gharials.
- Squamata: Lizards (e.g., Calotes), Snakes (e.g., Naja, Python).
- Rhynchocephalia: Sphenodon (tuatara — living fossil).
Special topic — Snakes (The Big Four in India)
- Cobra (Naja)
- Krait (Bungarus)
- Russell’s viper (Vipera russelli)
- Saw‑scaled viper (Echis carinatus)
First aid: immobilize limb, avoid tourniquets, get anti‑venom treatment at hospital ASAP.
3. Aves (Birds)
General characteristics
- Endothermic: Maintain high metabolic rate and stable body temperature.
- Feathers: Insulation and flight; forelimbs modified into wings.
- Skeleton: Hollow (pneumatic) bones; many fused elements for rigidity during flight.
- Respiration: Lungs with air sacs → continuous unidirectional airflow (very efficient).
- Circulation: 4‑chambered heart (complete separation of oxygenated & deoxygenated blood).
- Reproduction: Internal fertilization; hard‑shelled eggs (oviparous).
- Excretion: Uricotelic — conserve water by excreting uric acid paste.
Flight adaptations
- Streamlined body shape and strong pectoralis muscles.
- Feathers: contour, flight, and down for insulation.
- Lightweight but strong skeleton; fused bones (e.g., synsacrum).
- High oxygen extraction via air sacs and parabronchi supports intense aerobic activity.
Respiratory system (key points)
Small stiff lungs connected to 9 air sacs (usually). Unidirectional flow keeps parabronchi supplied during both inspiration and expiration — ideal for high‑altitude flight in some species.
4. Exam‑important comparisons
| Feature | Amphibia | Reptilia | Aves |
|---|---|---|---|
| Skin | Moist, glandular (cutaneous respiration) | Dry, keratinized scales | Feathers (keratin) |
| Respiration | Gills (larvae), lungs + skin | Lungs only | Lungs + air sacs (unidirectional) |
| Heart | 3‑chambered | Mostly 3‑chambered (crocodiles = 4) | 4‑chambered |
| Eggs | Jelly‑coated, non‑shell | Cleidoic (shelled) | Hard‑shelled |
Quick revision pointers
- Amphibians = transition from water to land → focus on respiration & parental care.
- Reptiles = first fully terrestrial vertebrates → focus on scales, eggs, and snake identification.
- Birds = flight specialists → focus on flight adaptations, respiration, and circulation.
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