Biology · Animal Kingdom · NEET
| Common name | Cold-blooded | Warm-blooded |
| Scientific term | Poikilothermous | Homeothermous / homoiothermous |
| Body temperature | Varies with the surroundings | Stays constant |
| Can regulate temperature? | No | Yes |
| Vertebrate classes | Fishes, Amphibia, Reptilia | Aves (birds), Mammalia |
| NCERT example | Frog (Rana tigrina), turtle (Chelone) | Parrot (Psittacula), camel (Camelus) |
A frog is cold-blooded (poikilothermous). NCERT says the common Indian frog Rana tigrina does not have a constant body temperature — its body temperature changes with the temperature of the surroundings. Frogs belong to class Amphibia, and all amphibians are poikilotherms.
Reptiles are cold-blooded (poikilothermous). This is a very common trap in NEET. Even though some reptiles like crocodiles have a four-chambered heart, they still cannot keep a constant body temperature. NCERT clearly groups fishes, amphibians and reptiles together as poikilothermous.
A poikilotherm (cold-blooded) cannot regulate its own body temperature, so its temperature rises and falls with the environment. A homeotherm (warm-blooded) keeps a constant internal body temperature using its own metabolism, whatever the outside weather. Poikilo = varied, homeo = same.
Only two vertebrate classes are warm-blooded: Aves (birds) and Mammalia (mammals). Every other class — Cyclostomata, Chondrichthyes, Osteichthyes (fishes), Amphibia and Reptilia — is cold-blooded. So out of the vertebrate classes, only birds and mammals are homeotherms.
Yes. Homeotherm, homeothermic and homoiothermous all mean the same thing — an animal that keeps a constant body temperature. NCERT uses the spelling 'homoiothermous' for mammals and 'warm-blooded' for birds. In exams treat homeotherm, homoiotherm and warm-blooded as identical.
No. Cold-blooded does not mean the animal is cold. It means the body temperature is not controlled by the animal — it simply matches the surroundings. A lizard sitting on a hot rock can be very warm. The word only tells you the temperature is not kept constant from the inside.
Birds and mammals have a high metabolic rate and a fully divided (four-chambered) heart that keeps oxygen-rich and oxygen-poor blood separate. This lets them produce and hold body heat, so they stay active in cold places. Insulation like feathers (birds) and hair (mammals) helps trap that heat.
Which one of these animals is not a homeotherm?
Which one of the following characteristics is not shared by birds and mammals?
Select the incorrect statements: A. Digestive system in Platyhelminthes is incomplete. B. Bilateral symmetry is a characteristic feature of adult Echinoderms. C. Pseudocoelom is possessed by Aschelminthes. D. Notochord is persistent throughout life in class Chondrichthyes. E. Members of class Reptilia maintain a constant body temperature.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Cyclostomata, Chondrichthyes and Osteichthyes (the fishes), Amphibia, and Reptilia are all cold-blooded (poikilothermous).
Only Aves (birds) and Mammalia (mammals) are warm-blooded (homeothermous / homoiothermous).
Poikilothermous means the body temperature is variable and changes with the environment because the animal cannot regulate it. It is the scientific word for cold-blooded.
Homoiothermous (also written homeothermous) means the animal keeps a constant internal body temperature regardless of the outside temperature. It is the scientific word for warm-blooded. NCERT uses this term for mammals.
NEET repeatedly tests which classes are warm- versus cold-blooded, often hiding it inside a 'select the incorrect statement' question (2016, 2018, 2026). Remembering that only birds and mammals are warm-blooded lets you eliminate wrong options instantly.
