Biology · Animal Kingdom · NEET
NCERT lists these flight features: (1) forelimbs changed into wings, (2) body covered with feathers, (3) endoskeleton fully ossified (bony) with long bones that are hollow and have air cavities — these are called pneumatic bones and they make the bird light, (4) air sacs connected to the lungs that supplement (help) respiration so muscles get enough oxygen during flight, and (5) a completely four-chambered heart that keeps oxygen-rich and oxygen-poor blood fully separate. Together these reduce weight and increase energy supply, which is why birds can fly.
Hollow bones make the skeleton much lighter without making it weak. NCERT says the endoskeleton is fully ossified (fully bony and strong) but the long bones are hollow with air cavities, called pneumatic bones. Less weight means less energy is needed to lift the body into the air. This is one of the most-asked NEET points, so remember: pneumatic = air-filled hollow bone = lighter for flight.
Birds are warm-blooded, also called homoiothermous. This means they keep a constant body temperature no matter how hot or cold the outside is. This is very different from fishes, amphibians and reptiles, which are cold-blooded (poikilothermous). Being warm-blooded gives birds steady, high energy for flying. In the NEET vertebrate grid, only Aves and Mammalia are warm-blooded.
Air sacs are thin sacs connected to the lungs. NCERT states: 'Air sacs connected to lungs supplement respiration.' They act like extra air stores that keep fresh air moving through the lungs, so oxygen supply stays high during flight. They do NOT do gas exchange themselves — that happens in the lungs. Air sacs also help make the body lighter. Do not confuse air sacs with the air bladder of bony fishes (that controls buoyancy in water).
No. Feathers and wings are the characteristic features of Aves, and most birds can fly, but some are flightless. NCERT gives Struthio (Ostrich), which is flightless and adapted for running, and Aptenodytes (Penguin), a flightless bird whose forelimbs are modified into paddle-like flippers for swimming. So a bird is still Aves even if it cannot fly — it is classified by feathers and other features, not only by flight.
Both are warm-blooded, have lungs, and have a four-chambered heart — so those are shared. The key difference NEET tests: birds (Aves) are oviparous (lay eggs), while most mammals are viviparous (give birth to young). Mammals also uniquely have hair and mammary glands, and their skin has glands. Birds have feathers, a beak, dry skin with only one oil gland at the base of the tail, and no teeth. So 'viviparity' is NOT shared by birds and mammals.
Which one of the following characteristics is not shared by birds and mammals?
Identify the vertebrate group of animals characterized by crop and gizzard in its digestive system
The flightless bird with forelimbs modified as paddle-like structures suited for swimming is known as:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Warm-blooded (homoiothermous). Only Aves and Mammalia are warm-blooded among vertebrates; fishes, amphibians and reptiles are cold-blooded (poikilothermous).
Birds have a completely four-chambered heart, just like mammals. This keeps pure and impure blood fully separate, giving high energy for flight.
Birds are oviparous — they lay eggs — and their development is direct. This is a common NEET trap because mammals are mostly viviparous.
A pneumatic bone is a long bone that is hollow and has air cavities inside. It keeps the bird's skeleton strong but light, which helps in flight.
No. Birds have a beak and no teeth. Instead, the gizzard grinds food. Their skin is dry with only one oil gland at the base of the tail.
