Movement and Locomotion
Category : 11th Class
Movement is one of the most important characteristics of living organisms. Nonliving objects do not move. If nonliving objects show movement, that is always due to some external force. For example, the cart is moved by the horse and the fan revolves by the energy of electric current. The movement of a nonliving object is, therefore induced (due to external force) while the movement of living things are autonomic (self sustained). Study of movement is called kinesiology (G. Kinein = to move, Logos = study). The movement of living systems are thus autonomic or active, that is effected by the organisms themselves without external influences. On the other hand the movement of nonliving systems are induced or passive, i.e., made to occur by external forces. Movement of animals are two main types muscular and non muscular.
(1) Muscular movement : Muscular movement are found in the majority of animals brought about by sliding of myofilaments. Muscular movement are further divide into two kinds – Locomotion and movement of body parts.
(i) Locomotion (locus = place + moveo = to move) : Locomotion is the movement of an animal as a whole from one place to another.
Types of locomotion : Locomotion takes several forms such as walking (man), creeping (earthworm, lizard), cursorial (Horse, flightless birds), hopping (frog, rabbit), running (dog, horse), flying (insects, birds) and swimming (fish, whale).
Animals have suitable adaptations for their specific mode of locomotion. Adaptations for running, hopping, swimming and flying are respectively called cursorial, saltatorials, natatorial, and volant adaptations. Morphogenetic movement, i.e., the streaming of cells in the early embryo to form tissues or organs, may be considered a form of locomotion.
Advantage of locomotion : Locomotion is helpful for animals as escape from predators, search of shelter, food and water, shift to favourable environment, reproduction, collect materials for nest building, locate suitable area for breeding and dispersal to new location. All forms of locomotion require energy to overcome two forces that tend to keep the animals stationary. These are friction and gravity.
(a) Swimming : Water is a much denser medium than air so body modified for swimming in the form of buoyancy, fusiform body etc. Mode of swimming varies in animals. fishes swim by moving their body and tail from side to side. Whales and dolphins swim by undulating their body and tail up and down. Insects and 4-legged vertebrates use their legs as oars to push against the water. Cuttle fish and squid are jet-propelled, taking in water and squirting it out in bursts.
(b) Locomotion on land : For walking, running, hopping and crawling on land, animal expends energy body to prevent falling down and move forward against gravity. Powerful muscles and strong skeletal support are more important for moving on land than a streamlined body. Creeping animals have their entire body in contact with the ground. Therefore, they make a considerable effort to overcome friction.
(c) Flying : Gravity is a major problem in flight. Wings must produce enough lift to make and keep the animal air-borne against the downward force of gravity.
(ii) Movements of body parts : Movement of the body parts help the animals in several respects.
(a) Movement of external parts : Appendages are vary in number and form in different animals. Many annelids have several pairs of flat parapodia, arthropods have 3 to many pairs of jointed legs, mollusks have an unpaired foot, echinoderms have numerous paired tube-feet, vertebrates have fins in fishes or limbs in all others.
Movements of head, trunk and appendages, enable the animals to assume favourable posture for rest and equilibrium. Movements of appendages, snout, mouth, jaws, tongue, etc., enable the animals to capture and ingest food. Movements of sense organs, namely tentacles, antennae, eyeballs and pinnae of the ears, help the animals to gather information about their external environment. Movements of buccopharyngeal cavity bring about water breathing in fishes and air breathing in amphibians, and movements of chestwall cause ventilation of lungs in other vertebrates. Movement of body parts also assist the animals in mating and feeding the young ones. Facial expression and gestures also result from movements. Vibrations of vocal cords produce sound in vertebrates, and of special abdominal plates in cicada. Rubbing the edges of forewings produces sound in grasshoppers.
(b) Movements of internal parts : Visceral movements make many vital activities possible :
(2) Non-Muscular movement : Besides locomotion and movements of body parts, some of the cells of multicellular animals move like unicellular organisms.
(i) Ciliary movement : The cilia present in the trachea, vasa efferentia and oviducts propel by their movements dust particles, sperms and eggs respectively. The cilia of flame cells of flatworms push excretory materials. Ciliary movements in Planaria or Dugesia also.
(ii) Flagellar movement : The flagella of choanocytes (collar cells) of the sponges maintain a regular current of water in the body. The flagella of certain cells of gastrodermis of hydra help in the circulation of food. Sperms move by flagellar movements.
(iii) Pseudopodial movement : Leucocytes and macrophages move by pseudopodial movement.
(iv) Cytoplasmic streaming movement : Streaming movement of the cytoplasm is called cyclosis. It is observed in most of the cells.
(3) Locomotion in different animals
(i) Locomotion in Protozoa : Locomotion in protozoans by the help of cilia, flagella and pseudopodia.
(ii) Locomotion in Porifera : Sponges are sedentary or fixed animals which are always attached to some substratum. Hence locomotion never takes place.
(iii) Locomotion in Coelentrates : Locomotion in coelentrates is largely due to the contraction of the epidermal muscle fibres following type of movements take place in coelentrates -
(a) Swimming (b) Floating (c) Surfacing (d) Climbing
(e) Walking (f) Gliding (g) Somersaulting (h) Looping
(i) Bending swaying movement.
(iv) Locomotion in Helminths : In helminths (platyhelminthes and aschelminthes) locomotion not required by adult due to parasitic adaptations. However in miracidia (a larva) locomotion by cilia, in cercaria larva by tail. In Ascaris 15% locomotion by cuticle fiber. In planaria locomotion by cilia and muscles.
(v) Locomotion in Annelids : Leech, Earthworm and Nereis have well developed circular and longitudinal muscles in the body wall that help these animals to move about. Parapodia and setae helpful for locomotion in nereis. In earthworm also locomotion by setae.
(vi) Locomotion in Arthropods : In arthropods locomotion takes place with the help of jointed legs, and a pair of wings. Cockroaches, housefly etc., move from one place to another by legs (walking) as by wings (flight) both. Palaemon or prawn crawls at bottom by pairs of walking legs. Palamnaeus or Indian scorpion used 4 pairs of walking legs. All insects used 3 pair of walking legs for locomotion.
(vi) Locomotion in Mollusca : In all the molluscs, the locomotory organ is a thick walled, muscular, broad or laterally compressed foot. In some molluscs, the foot is modified into eight or ten arms (e.g., Sepia, Loligo, Ocotopus etc). Foot is chiefly a locomotory organ in unio and pila both. In Neopilina also locomotion by foot. In sepia, loligo locomotion by fins mainly.
(viii) Locomotion in Echinodermata : In echinoderms such as starfish, the locomotory organs are tubefeet and locomotion takes place by water vascular system, which set up a hydraulic pressure. The tubefeet are associated with this system intimately. At the time of locomotion, one or two arms of a side work as main structures.
(ix) Locomotion in vertebrates : In vertebrates, locomotion takes place with the help of skeletal muscles, and skeleton. The locomotory organs are a pair of legs.
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