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Saturday, 22 December 2018

Movement and Locomotion





Movement is a general term meaning the act of changing position. Locomotion is the movement of the whole organism from one place to another. The latter is an important characteristic of most heterotrophic organisms, especially animals.

    In living organisms, movement is brought about mainly by pseudopodia, cilia, flagella and muscles. Many simple motile organisms move from place to place using pseudopodia, cilia PR flagella.

Pseudopodia : Amoeba moves by using pseudopodia, which are temporary projections of the cell. Pseudopodia formation is brought about by

• The Sol gel sol (I.e.  liquid semisolid liquid) transformations, and 
• The streaming movement of the cytoplasm. In amoeba, the cytoplasm is composed of two parts:

• An outer ectoplasm which is a semi solid or plasmagel, and 

• An endoplasmic within, which is a fluid PR plasmasol. 

At the part of ectoplasm where a new pseudopodium is forming (anterior end), the plasmagel liquifies. Plasmasol from within the cell streams forward into this part forming a projection, the new pseudopodium. Immediately, the plasmasol in the outer part of  the new pseudopodium solidifies into plasmagel to form ectoplasm. Simultaneously, a pseudopodium is withdrawn from another part (posterior end) of the cell by liquefaction of the ectoplasm there.

    Multicellular organisms too have cells which move by pseudopodia. Examples include digestive cells in the gut of the hydra and the white blood cell in humans.

Flagella : The trypanosoma moves by using a flagellum. The flagellum is a long tube of cytoplasm that projects from the cell surface r. It has a constant beat that produces waves along its length, and also makes it move in a spital manner.

    Usually, the flagellum is at the rear and of the cell, from where its action propels the organism forward.

   Motile gametes of multicellular organisms, including human spermatozoa, move by the action of flagella.

Cilia : Paramecium moves by the coordinated beat of its numerous cilia. Cilia are like flagellum in structure except that they are much shorter and occur in large numbers, arranged in rows in the cell surface e. The beat of cilium, however , is not  constant. It has two phases: a rapid and a slow one. To propel the organism forward, the cilium behaves like a stiff paddle and pushes back against the water rapidly. This is the driving or effective stroke. Then, cilium becomes flexible and bends as it slowly returns to its starting position, in the recovery stroke.

   In many multicellular organisms, ciliated cells are used to move fluids over tissue surfaces. For example, the beating action of the cilia of the cells lining

• The fallopian tube in humans moves the egg cell along the tube to the uterus; and 

• The breathing passages in humans moves mucus ( which traps dust and dirt in the inhaled air) up towards the throat.

    Cilia, flagella and pseudopodia are mainly used for the locomotion of simple organisms. In higher animals, locomotion is brought about by muscles attached either to the exoskeleton or the endoskeleton.

Muscles : In mammals, there are three types of muscles:

• Smooth, 
• Cardiac
• Skeletal

Of these , the skeletal muscles bring about movement by pulling on the skeletal parts of which they are attached. This is the type of movement that is responsible for locomotion.

   Muscle tissue is made up of specialized elongated cells or fibres which can contract, I.e. shorten and thicken, to bring about movement. Skeletal muscles are under voluntary control, which means that we can consciously bring about their environment. Smooth and cardiac muscles are under involuntary control, we cannot control their movements.

Smooth muscle : This muscle is composed of elongated spindle shaped cells which are grouped into bundles or sheets. They are the last specialized muscle cells and are under the control of the autonomic nervous system. Smooth muscles contract slowly and fatigues slowly. They occur in the walls of the gut, blood vessels and respiratory tract.

Cardiac muscle : This muscles is not only found in the walls of the heart. The muscles cells are branched and connected to one another by special disc. These discs help the cells to contract and relax in unison so that the heart can pump rhythmically. The cells can carry on contracting and relaxing even when the heart is taken out of the body. However. The rage of contraction is influenced by the automatic nervous system.

Skeletal muscle : This muscle is so named because it is attached to the bones it moves. About 40%, of a human male's body and 23% of a female's body are composed of skeletal muscle.

     A skeletal muscle consists of bundles of cylindrical muscles arranged in a parallel manner. Each bundle is enclosed in connective tissue, and all the bundles are again collectively wrapper in connective tissue. At the ends of muscle, the connective tissues extend to form tendons which attach the muscle to bones. 

    Contraction of skeletal muscles occurs when they are stimulated by motor nerves from the brain or spinal cord. Skeletal muscles can contract rapidly and powerfully. Their contraction is a high energy consuming process. The energy comes from ATP which is provided by aerobic cellular respiration
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