All living things are made of cells which are differentiated to perform different functions. Substances move into or out of the cell and enzymes are catalysts contributing to cell metabolism. The ...

To focus on a distant object – the lens is pulled thin, this allows the light rays to refract slightly.

The metabolic activity of any tissue is limited by its blood supply; the more active any organ, the more blood it needs and the more extensive its vascularization. The changes in metabolic activity ...