Movement is the ability of living organisms to move from one place to another.
Reasons for movement include searching for food, escape from danger, response to stimuli (either positively or negatively) and for the sake of reproduction. All organisms that can move are equipped with various organelles or organs and mechanisms for movement.
Cyclosis is the circulation of protoplasm in cells. In animals, cyclosis occurs in protozoa like Amoeba popularly known as amoeboid movement. Amoeboid movement is aided by a mechanism called cytoplasmic streaming. It involves the principle of gel-sol conversion of cytoplasm, i.e ., the varying of the viscosity of cytoplasm and the accompanying fluid pressure at different points within the cell membrane.
Movement in Amoeba proteus is accompanied by a continuous streaming of the cytoplasm in the forward direction. This movement is accompanied by the locomotion of the whole cell. In the forward direction, the central plasma sol is converted to plasma gel which remains attached to the inner wall of the plasma membrane but at another point, the gel is reconverted into a sol thereby creating pseudopodium in front and the driving force from behind.
Organelles for Movement
Organelles which cause movements affecting the whole cells and leading to cellular locomotion in Paramecium, Chlamydomonas and Euglena are flagella and cilia.
Flagella: These are long whip-like projections on the cell surface. They are usually one or two on a cell,e.g. Euglena, Chlamydomonas, Spermatozoa, Trypanosome, etc. The flagella (singular, flagellum) are the organelles of movement in these organisms.
Cilia: Cilia are short, hair-like structures that project out of the cell’s surface.
They are usually numerous and packed closely together. They move in a co-ordinated way to bring about movement. In the Paramecium, the action of the cilia moves the whole organism; at the same time it also directs a current of water containing food into the Paramecium’s gullet. In the cells lining the human windpipe, the beating of the cilia causes mucus to move up towards the throat.
The bending of a part of plant to any particular direction may be due to the relative auxin concentration. This shows that the growth movement in plant which are involved in tropism are brought about by auxins.