Movement

Movement is another characteristic of living things. It does not always mean locomotion or movement from one place to another. In animals movement is quite obvious. We move our arms and legs; we also move from place to place. Most animals can move in this manner at least at some stage of their life. Movement in plants is not so obvious. However, if you observe plant cells under a microscope, you can see streaming movement of cytoplasm within them.

This is called cyclosis. Some plants like Mimosa and Venus's flytrap show obvious movements, as you have read before.The mode of locomotion in animals varies. Some lower animals move about by the beating of tiny hair like cilia or longer flagella. Some like amoebae move about using pseudopodia, which are temporary extrusions of cytoplasm. A few animals such as sponges, corals, oysters and certain parasites do not move from place to place.

However, most of these have free swimming larval stages. Moreover, even in the sessile adults, cilia or flagella or tentacles move rhythmically.Thus you find that one or more of the above characteristics distinguish living things from the non-living. However, the most important of these criteria is reproduction because that is the most unmistakable characteristic of living things.