Growth and development
Many living things begin life as a single cell, from which a new and independent organism slowly takes shape. This remarkable sequence of ever is the result of two different but closely linked processes. The first these is growth, which is simply an increase in size. The second is development, when is an increase in complexity. Cells work best when they are of a particular site so living things usually grow by making more cells, rather than by enlarging the cells that they already have. New cells are made by cell division, and this can happen in two ways. One form of division, called meiosis, is used only if sexual reproduction (p.38). Another form, which is often called mitosis, is up for growth. Mitosis involves the cell nucleus splitting in two. The rest of the cell then divides, and two new cells are produced. Early on in life, cell division occurs at a very rapid rate and millions or billions of new cells can quickly build up. These new cells gradually begin to differentiate, or develop different characteristics, and eventually a mature organism is forme When this organisms reproduces, the next generation is brought into begin, and the cycle of growth and development begins all over again.