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16. Support and Movement eLearn.Punjab

Passive flight; When birds glide, the wings act as aerofoils. An aerofoils is any smooth surface

which moves through the air at an angle,to the airstream. The air flows over the wing in such a way
that the bird is given lift; the amount of lift depends on the angle at which the wing is held relative
to the airstream.

Active flight: When little or no support can be gained from upward air currents, the same effect

can be achieved by flapping the wings. As the birds moves through the air, the air flows more
quickly over the curved upper surface than over the lower surface. This reduces the air pressure on
the top of the wing, compared with air pressure below the wing. There is, therefore, a net upward
pressure on the wing which gives lift to the bird.

Locomotion in Mammals

The most efficient way of supporting the body is seen in mammals. The limbs of the mammals have
undergone further modifications to produce the following modes of locomotion.

1. Plantigrade : In this mode of locomotion the mammals walk on their soles with palm, wrist,

and digits all resting more or less on ground, such as monkeys, apes, man and bear etc.

2. Digitigrade : Some mammals tend to walk on their digits only. They run faster than plantigrade

animals. In these mammals, first digit usually reduces or completely lost as in rabbit, rodents etc.

3. Unguligrade : These mammals walk on the tips of toes modified into hoof as deer, goat. It is

the most swift type of locomotion.

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