THE MECHANISM OF LOCOMOTION IN ANIMALS

•Describe briefly the mechanism of locomotion in an animal

Locomotion in an earthworm• Earthworms have a

hydrostatic skeleton.

• Circular and longitudinal muscles of the body wall press against the fluid, creating a pressure in the fluid to maintain the shape of the earthworm.

• Movement of the earthworm is brought about by the contraction and relaxation of the circular and longitudinal muscles alternating each other (antagonistic).

– When the earthworm moves forward, the circular muscles at the anterior end contract. The compressed fluid cause the relaxed longitudinal muscles to lengthen. The segments extend and the body moves forward

– Following this extension movement, the longitudinal muscles at anterior end contract, the circular muscles relax and body shorten

Locomotion in a grasshopper

• Grasshopper has a hinged exoskeleton.

• 3 pairs of legs. It hind legs are big and very strong – use for jumping.

• Before jumping the hind legs are folded. The contraction of the extensor muscles in the hind legs extends the leg and pushes against the ground. The thrust created propels the grasshopper forward and upward.

• Apart from jumping, the grasshopper has claws and glandular pads at the end of the each leg to enable it to walk upside down and climb up smooth vertical surfaces.

• The grasshopper also has wings on its thorax hat enable it to fly. The wings are flattened extension of the exoskeletons.

• The contractions of the thoracic muscles move the wings, producing a lifting force to lift the grasshopper and allow it to fly.

Locomotion in a fish• Fish are vertebrate animals

which live in fresh or sea water

• Water, particularly sea water, has a high relative density, providing resistance to the fish movement. Most fish overcome this problem by streamlining.

• The tail has a broad caudal fin which increase the surface area. The side-to-side lashing of the tail is brought by the myotome muscles which produces a forward thrust to drive the fish forward in the water

• There is a tendency for the fish to become unstable in the water during movement. This leads to yawing, rolling and pitching movements. This movement are control by fins.

• The fins give stability and control the direction during swimming.

• Bony fishes have an air filled swim bladder beneath the spinal column. The pressure in the bladder can be increased decreased by gulping or releasing air through the mouth. This keeps the fish buoyant when it stop swimming.

TYPES OF FINS

FUNCTION

PECTORAL FIN •Control the pitch of the fish, causing it to swim upward @ downward.•Help in slowing down @ stopping

DORSAL FIN •Controls rolling & yawing of fish

PELVIC FIN •Control the pitch of the fish•Control the rolling of the fish

VENTRAL FIN •Controls rolling & yawing of fish

Locomotion in a bird• Birds have many special

modification which are adapted for efficient flight.

• Modification of the adaptation is to reduce the bird’s weight. There includes: Hollow bones Some paired organs such as kidneys and testis, occurring as a single organ

Small brain Absence of teeth Small head Absence of sweat glands No storing of fat

• The air is a medium which does not provide much support for flying.

• Therefore, the bird overcome this problem by having wings acts as aerofoil.

• The wings are attached to the sternum by large, powerful muscles known as pectoralis major and smaller muscles known as pectoralis minor.

• The contraction and relaxation of the muscles give the flapping movements of the wings

• The movement of the wings creates a flow of air over the wings, with the speed of air faster on top of the wings

• This is due to the aerofoil shape of the wings. This causes a higher pressure under the wings according to Bernoulli’s Principle. A lifting force is then produced to enable the bird to fly.

• The shape of the bird and a layer of waterproof feathers give the bird a streamlined body to overcome air resistance during flight.