Monday, May 2, 2011

Animal and Plant Cells

All living things are made of cells and part from those of the bacteria the cells all have much the same internal structure, although their external appearance varies enormously according to the jobs they have to do. A variety of animal cells are shown on the right below. There are several hundred different kinds of cells in the human body, and the total number of cells may exceed ten trillion. Most of them are obviously extremely small, and it is only recently that powerful microscopes have revealed their detailed structure. The nucleus the most conspicuous of the internal structures or organelles is the cell’s control center. It is bounded by the nuclear membrane and it contains the chromosomes that carry all the hereditary material. The nucleus produces the ribosomes, which themselves are responsible for the formation of the cell’s proteins. This takes place on the surface of the endoplasmic reticulum, which is a network of flattened and connected to the nuclear membrane and spreading throughout the cell.