Locomotion in animals Definition

Locomotion in animals
Locomotion is defined in different ways such as:
Movement or capability of an organism to go or move from a place to another place.

Locomotion in biology pertains to the various movements of organisms to propel themselves from one place to another.

It is the active travel from place to place.it requires energy expenditure to overcome two forces:
Word origin:
The word locomotion is derived from the Latin word locus (place) and motio (motion) which means movement from place to place.

Modes of locomotion:
Locomotion used by the animals depends upon:
The size of the animal
The habitat of the animal
For example, land animals are capable of terrestrial locomotion because they have specific adaptations for it. For example, for running and walking they have feet and strong limbs. For animals without limbs, like snakes, they can slip over the surfaces. Animals having long hind limbs have ability to jump high. Animals living in the water, like fishes, move from place to place by using their fins. Unicellular organisms, like ciliates and flagellates, move by cilia and flagella. Animals, like bats, squirrels climb from one tree to another and this type of locomotion is called arboreal locomotion.

Importance of locomotion:
Locomotion plays a very vital part in the lives of all the living things. Most of the animals move to stay away from their predators and for survival with the result that the natural selection shaped the modes of locomotion and the ways or mechanisms used by moving organisms. Animals change their positions or move from place to place due to several reasons. Some of them are as follows:
To find food to grow and to get energy from that food
To find a mate and to reproduce
To find a suitable microhabitat to live
To escape from predators
To protect themselves from damage from pressure, pain or sudden temperature changes
To find shelter from bad environment
Locomotion in protoctista
Protists have different modes of locomotion to move from one place to another. Protists have adapted five different locomotry methods. These modes are:
Pseudopodial locomotion
Flagellar locomotion
Ciliary locomotion
Wriggling locomotion
Mucilage propulsion
1.Pseudopodial locomotion:
It is a very slow method of locomotion in which the animals creep with the help of different projections or finger like outgrowths that arises from the protoplast. These projections are called pseudopodia. Sarcodines and slime moulds show such type of locomotion.

Types of pseudopodia:
There are four types of pseudopodia discussed below.

Lobo podia:
These are the large and blunt extensions of the cell body and contains both endoplasm and ectoplasm. Amoeba moves by lobo podia.

These pseudopodia are fine, thread-like, tapering, and are composed of ectoplasm. These are found in Euglypha.

These are long and stiff, with hard axial filament. These pseudopodia are present in Actinophryid.

These are long and branching. These pseudopodial branches unite and forms a net like mesh. These are found in Globigerina.

Locomotion in Amoeba:
Pseudopodia are the locomotry organs in amoeba. These are finger like projections thrown in the direction the flow of the cytoplasm consequently, the body moves in that direction.

2. Flagellar locomotion:
Flagella shows whip-like movement. They usually beat independently. Such type of locomotion is displayed by the dinoflagellates (Gonyaulax), euglenoids (Euglena) and zoo flagellates (Leishmania).

Locomotion in Euglena:
Euglena is a very active micro-organism and moves very fast. Movement is caused by the lashing movement of the long flagellum against the surrounding water. The flagellum is present on the anterior side of the organism. The whipping action of the flagellum causes it to rotate and simultaneously moves forward. The flagellum has 9+2 arrangement of the fibrils. Five fibrils will contract simultaneously to bend flagellum, then four fibrils will contract simultaneously to straighten the flagellum.

To change its direction euglena uses the myonemes which are the contractile structures made up of a long chain of proteins and are present on the whole length of its body. When the myonemes contract the shape of the body is changed as well as its direction. The movement displayed by Euglena is known as euglenoid movement.

Ciliary locomotion:
Movement exhibited by the cilia is oar like. All the cilia of a cell show coordinated movement which is of two types:
Isochronic rhythms
Metachronic rhythms
In isochronic or synchronous rhythm, all the cilia of a cell beat at the same time. In case of metachronic rhythm they do so in rapid succession one after the other. It occurs in ciliates (Paramecium).

Locomotion in Paramecium:
Paramecium moves very fast with the help of cilia. It is called ciliary movement. Not all the cilia move at the same time, but a group of cilia moves gradually like a wave. This wavy movement of the cilia begins from the anterior end and moves backward.

Structure of cilia:
These are short, very thin thread like projections that arises from the plasma membrane. Their length ranges from many microns to many hundred microns and the diameter varies from 0.1 to 0.5 micron.

Mechanism of movement:
This movement was explained by the Bradford in 1955 who said that the sliding movement of the double fibrils of the cilia in two groups is responsible for the movement of the cilia.

a. Effective stroke: Five out of nine double fibrils contract or slide simultaneously.

As a result, cilium bents and shortens. this is called effective stroke.

b. Recovery stroke: Four out of nine double fibrils contract and cilium becomes straight. This is said as recovery stroke. Because of this Paramecium swims against water.

Wriggling locomotion:
It is a slow wave like locomotion. This movement is caused by the wave of expansion and contraction in the body of the organism such as sporozoans, zoo flagellates, euglenoids.

Locomotion by mucilage propulsion:
Some protists lack any specific organ of locomotion like diatoms. For locomotion these organisms secrete mucilage. The organism is expelled in the direction opposite to that of the direction in which the mucilage is secreted.

Locomotion in other invertebrates
The organs of locomotion in lower animals vary a lot. They may use wings, tube feet, muscular feet or walking legs as means of locomotion. Some invertebrates like round worms, flatworms, squids, octopus and jellyfish lack special organs of locomotion. Out of these animals some are pushed by the expansions and contractions of their body muscles while others move by pumping water or by jet propulsion.

Locomotion in Earthworm:
The organs of locomotion are setae or bristles which are present externally on each segment. The setae of the posterior part become extended and attach to the ground. The longitudinal muscles are then relaxed, and circular muscles are contracted. As a result, anterior part moves forward over the surface of the soil. Then the setae of the anterior part extend and hold the soil surface and setae of the posterior part are withdrawn. Now the circular muscles relax and the longitudinal muscles contract. As a result, the posterior end of the organism is drawn forward. The posterior end is again fixed, and the anterior end is extended forward. This whole process is repeated again and again. So, an earthworm shows an accordion like movement.

Locomotion in cockroach:
Cockroach has three pairs of legs and two pairs of wings. There are two modes of locomotion in cockroach.

The posterior pair of the wings bring about flight. These beat in air in such a manner that they support the body weight and drive it through the air.

In walking, the legs of one side are used. The forelegs pull the body forward and the hind legs pushes it in the same direction. The middle leg of the opposite side acts as a prop. The remaining three legs begins to move together, and the process is repeated. For movement of the legs antagonistic pairs of the muscles are used.

Locomotion in snail:
Snail and mussels are molluscs and crawl or move very slowly by foot.locomotion in snail takes place with the support of strong muscular foot present under the shell. A snail secretes a layer of mucus like slime and then uses its long, muscular feet to crawl on that layer of mucus. These waves move rapidly and produces enough force that pushes the snail forward.

Locomotion in starfish:
Starfish moves by the tube feet that are alternatively attached on the substratum. In the direction of movement arms are raised. The sucker contracts by circular muscles due to which the tube feet elongates and move forward and adhere firmly to the substratum by vaccuum action of the sucker. The tube feet take a vertical posture with the help of muscular activity. Hence the body is pushed forward. Then the tube feet contract with the help of longitudinal muscles and forces some water back to their ampullae. Then the sucker releases their hold from the substratum.

Locomotion in vertebrates
In vetebrates skeletal muscles or skeleton helps in locomotion. Vertebrate locomotion can take various forms including swimming, crawling, walking, flight, as well as some more idiosyncratic gaits such as hopping, brachiation, and burrowing.

Locomotion in Fishes:
Swimming in water presents very different problems than walking on land like a man or flying in the air like birds. The adaptations for walking efficiently through the water are:
Streamlined body:
The body of the most of the fishes is streamlined which means tapered at both ends. Hence water flows rapidly and readily over the body surface drag force is reduced at a minimum. Apart from the fins no other structures projects from the body of the fish and it seems that faster the fish, more perfect is the streamlined.

Mucus or oil glands:
The dermal denticles of the cartilaginous fish the scales of bony fish are moist by slimy exudation from mucus or oil glands and this also considerably reduces friction between fish and water.

The dorsal and ventral, unpaired fins help to stabilize the fish. The paired pectoral and pelvic fins are used for steering and balancing the animals. The caudal or tail fin, along with paired fins, provide further movement of the fish through the water.

Swim bladder:
Buoyancy in the water is maintained by a specialized structure in bony fish called swim bladder.

Locomotion in amphibians:
The general build of a body is essentially fish like in amphibians. Such forms have two means of locomotion that are as follows:
The body of the amphibians have segmentally arranged muscles. These muscles help them to wriggle or twist on the land. It looks like swimming on land. When they wriggle on the ground, their legs hardly touch the ground.

Some amphibians have adapted swimming and jumping methods of locomotion. They uplift their body with the help of muscular systems which expels them along, by means of extensor thrusts of both kinds limbs, acting together. Frogs and toads have strong hind limbs. These limbs help them to walk and jump in the terrestrial environment.
Locomotion in reptiles:
Reptiles have adapted better modes of locomotion than amphibians as skeleton have evolved in them. Mostly their modes of locomotion are walking and running. Their general form of skeleton is like those of their ancestors, amphibians. They have developed many modifications for locomotion.
Reptiles have cervical vertebrae. The first two cervical vertebrae, called atlas and axis, are involved in the movement for head. The axis is modified for the rotational motion. The ribs of the reptiles have also modifications for locomotion. Their flexible bones of the ribs are connected to their large belly muscles. This modification also helps in locomotion.
Many primitive reptiles walk on their hind limbs. Such reptiles were called bipedal. Their pelvis was restricted and narrow and they had expanded broad tail to keep the body in balanced state. The animals that used only their hind limbs for locomotion, their forelimbs became modified for prey capture or for flying in some reptiles.

Locomotion in birds:
Their skeleton is modified in such a way that to support them for flying. Some of the modifications are as follows:
One of the most important modification is the evolution of such bones having large air spaces. Due to large air spaces their body weight reduces which helps them in flight.
Their fore limbs are modified into wings attached with the strong pectoral muscles which helps in the movement of the wings. These muscles help the wings to move up and down.

Another most important and obvious adaptation is the formation of keel. This structure is formed by the modification of the sternum. It provides the place of attachment of muscles.

Their body is covered with the feathers. These feathers increase the surface area of the wings. Larger surface area of the wings helps in flight.

Birds keep their bodies warm which helps them to produce enough energy for flight.

The bodies of the birds are streamlined which reduces the forces of friction and gravity and makes the flight easier.

Their feathers lie smoothly against their body hence air can pass easily over them.

There are two types of flights in birds:
Active flight
Passive flight
Active flight:
When the birds cannot gain any support from the upward currents of the air, then flying can be gained by the flapping of wings. When the birds fly in air, air slip past more quickly from the upper curved surface than the lower surface. Hence the air pressure decreases on the upper surface than on the lower. There is, therefore, net upward pressure which gives the bird a flight.

Passive flight:
Birds fly passively by gliding. During gliding their wings acts as aerofoils. The smooth surface which moves through the air at angle to the airstream is called aerofoil. The air flows over the wings. The flow of the air is such that it provides the bird a lift. The amount of the lift provided by the air flow depends upon the angle at which the wing is held relative to the airstream.

Locomotion in mammals:
Most efficient way of supporting the body is seen in mammals. Like most of reptiles, majority of the mammals move across land. The legs of the mammals originate from beneath their body which helps in moving to and fro while the legs of the reptiles arise from the side of their body. They use tendons for locomotion. Their limbs are modified to support the following modes of locomotion.

In this mode of locomotion, the mammals used to walk on their soles with palm, wrist and digits all lending to rest on the ground, such as monkeys, apes, man and bear etc.

Some mammals tend to walk on their digits only. They run faster than plantigrade animals. In these mammals the first digit usually reduces or completely lost such as rabbits, rodents etc.

These mammals walk on the tips of the toes modified into hoof such as deer, goat etc. it is the swiftest type of locomotion.