Q.(a) Write in detail the general characteristics of class Mammalia. OR

Class Mammalia is characterised by warm-bloodedness, hair/fur, milk-producing mammary glands, a muscular diaphragm, differentiated (heterodont) teeth, a four-chambered heart, and mostly viviparous reproduction — a combination of features not seen together in any other vertebrate class.

The general characteristics of class Mammalia include:

1. Warm-blooded (homeothermic) — mammals maintain a constant, usually elevated, internal body temperature independent of the environment, which supports a high, sustained metabolic activity level.

2. Hair/fur — the skin bears hair (at least at some stage of life, even in mostly-hairless mammals like whales), which insulates the body and helps regulate temperature.

3. Mammary glands — females possess mammary glands that secrete milk to nourish their young after birth; this is the single defining feature that gives the class its name.

4. External ear (pinna) — most mammals have an external, often mobile, ear flap (pinna) that helps collect sound, a feature largely absent in other vertebrate classes.

5. Heterodont, diphyodont dentition — teeth are differentiated into different types (incisors, canines, premolars, molars) suited to different functions (heterodont), and mammals typically develop two successive sets of teeth in a lifetime, milk (deciduous) teeth followed by permanent teeth (diphyodont).

6. Diaphragm — a muscular sheet separates the thoracic cavity from the abdominal cavity and plays a key role in efficient breathing (ventilating the lungs).

7. Four-chambered heart with a single left aortic arch — ensuring complete separation of oxygenated and deoxygenated blood, supporting a high metabolic rate.

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