Growth

A cell grows by increasing in mass and size (volume). The increase is due to the addition of more protoplasmic material. When the cell reaches its maximum size  it stops growing.

   Growth is an anabolic process. For it to occur, the cell needs plenty of good to provide the necessary energy and materials for building up  new protoplasm.

   In a unicellular organism, the young organism grows until it reaches its maximum size; then it reproduces to give rise to young individuals. This usually happens by simple division of the adult cell into two daughter cells as in amoeba.

    All multicellular organisms begin life as a single fertilized cell. This cell divides into two, then into four and so on. At the beginning , the fertilized cell just divides to form smaller cells, there is no increase in size. Cell division is , therefore, the basic of growth in a multicellular organism. It brings about an increase in number of cells.

    After cell division, the daughter cells increase in mass and size, I.e. enlarge. Eventually, each  cell may develop into a special type of cell by changing its shape and structure to carry out a particular function. The kind of cell it becomes depends on its position in the body of the organism. In our body, a cell may develop into a nerve cell if it is in the brain, a muscle cell, if it is in the heart, or a ciliated lining CE of it is in the trachea. This process is called cell differentiation and is important in the growth and development of a mature  multicellular organism.

   In a multicellular organism, during the early stages of growth and development, all the cells can divide. These cells may also rearrange themselves so that they can enlarge and differentiate  to give rise to the various parts of an organism in an orderly manner. In s mature organism, cell division is usually restricted to cells in certain regions of the body only. This is because most specialized cells lose their ability to divide.