The primary way that animals grow and develop is by building more cells. When an animal eats food, its body breaks the food down and uses it to fuel its energy requirements and build new cells through the process of mitosis. These new, or daughter, cells are often similar in size to the old, or parent, cells.
To produce more cells, animal cells divide in two. The process is complex, as the parent cell must produce new organelles for each resulting daughter cell, copy the genetic code as accurately as possible and transfer both copies of the genetic code into the nuclei of the daughter cells. Scientists call this process mitosis. This process requires energy, which must come from the animal’s food, along with the raw materials for constructing more cells.
Animals use a variety of chemical processes to convert this food into new tissues; the combination of all of the various chemical processes is called metabolism. During catabolism, the first step in the process, food is broken down into its constituent molecules. The second step in the process of metabolism is called anabolism. Anabolism produces new cells from these raw materials.
This method of growth, which relies on cell division, differs from that of plants. Plants primarily grow through the enlargement of existing cells, with less emphasis placed on the production of new cells.