Earthworms use hydrostatic skeleton and antagonistic muscles to move forward by extending segments through fluid compression. Grasshoppers use strong hind legs and wing contractions to jump and fly. Fish rely on tail lashing and fins for stability and thrust in water. Birds evolved light bones and wings for lift via flapping, overcoming air resistance.

1. THE MECHANISM
OF LOCOMOTION
IN ANIMALS

2. • Describe briefly the mechanism
of locomotion in an animal

3. 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).

4. – 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

5. 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.

6. • 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.

7. 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

8. • 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.

10. TYPES OF FUNCTION
FINS
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

11. 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

12. • 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

14. • 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.