Animals move from place to place in search of food and shelter. On the contrary, most plants remain fixed at a place because they can manufacture their own food. Locomotion is defined as the act of moving from place to place.
Locomotion in Animals:
Movement in animals can be of the following types:
1. Amoeboid motion:
Movement with the help of extensions of the body called pseudopodia is called amoeboid movement. Amoeba moves slowly in water by extending its pseudopodia. Pseudopodia are not permanent structures but are just extensions of cytoplasm in the direction in which the movement has to occur.
2. Ciliary motion:
Movement with the help of numerous, fine hair-like processes called cilia is called ciliary motion as seen in paramecium.
3. Flagellar motion:
Movement with the help of one or two long whip-like processes called flagella as in euglena and chlamydomonas.
4. Muscular motion:
Movement, which involves the use of muscles only or both bones and muscles, is called muscular motion. Most animals show muscular motion. Let us study a few examples:
- Hydra moves with the help of its foot and tentacles. It moves by quick looping movements.
- Earthworms move with the help of repeated contraction and relaxation of their muscles.
- Fish have fins and tail for locomotion. Fins and tail have a bony skeleton inside for support. Therefore, movements involve both bones and muscles.
- Snakes show creeping movement. Bodies of snakes are covered with scales, which help them in movement.
- Hind-limbs of frogs have webbed feet, which help them in swimming.
- Birds have wings for flying and well-developed chest muscles to support the movement of wings.
- Webbed feet of ducks act as oars and help them to swim.
Locomotion Human Beings:
Locomotion in humans is brought about by the coordination of two organ systems: skeletal system and muscular system.
Skeletal system: Human skeleton is made up of 206 bones. Bones help in the attachment of muscles and provide advantage for locomotion. Thus, when the muscles pull these levers, movement like opening and closing the jaws and flexing of arms are produced.
Functions of the skeletal system:
1. It forms a rigid structural framework of the body giving shape and form to the body.
2. It protects the delicate internal organs of the body. For example, skull protects the brain, eyes and ears and the vertebral column protects the spinal cord.
3. Skeletal system and the muscular system jointly bring about locomotion and movements. Muscles are connected to bones by means of bands of strong and flexible connective tissue called tendons.
Two bones fit into each other rat places called joints. Movement of the skeletal system actually occurs at the joints. Movements are produced at eh joints by contraction and expansion of the muscles attached to them. Bones of the skeletal system cannot move on their own. Bones are connected to each other at eh joints by tough, yet flexible connective tissue bands called ligaments.
Movement of the arm at the elbow joint is brought about by two muscles, which contract to produce opposite movements- the biceps and triceps. When one of these muscles contracts to produce movement the other one must relax to allow that movement to take place. When you move your arm up, the biceps contract pulling the arm up while triceps relax allowing the arm to be pulled up. When you straighten the arm, biceps relax while the triceps contract bringing down the raised arm.
Movement in Plants:
Most plants do not move around from place to place. However, some plants like volvox and chlamydomonas move from place to place by means of flagella. Plants like spirogyra and many weeds are free-floating and are carried to different places by the water current.
Different parts of the plant body do show several types of movements. Plant parts may move in response to light, gravity, water or touch. Thus, plant roots move in response to gravity while stems move in response to light. Leaves of oxalis or clover remain open during the day and fold up at night. Leaves of touch-me-not plant fold up when touched.
Movement in Response to Stimuli:
Living organisms respond to different stimuli in different ways. They respond either moving towards the stimulus or away from it. Response of an organism towards or away from a stimulus is called taxis. Movement in response to light is called phototaxis while movement in response to gravity is called geotaxis. You know that moths are attracted to light. Thus, they exhibit positive phototaxis while cockroaches and termites exhibit negative photo-taxis since they shun light.