Human life is characterized by a variety of functions that are essential for survival and well-being. These functions include metabolism, movement, development, growth and reproduction.

Metabolism

The basic function of an organism is to consume energy and molecules in foods, convert some of it into fuel for movement, sustain body functions, and build and maintain body structures. There are two types of reactions that accomplish this: anabolism and catabolism.

Anabolism is the process whereby smaller, simpler molecules are combined into larger, more complex substances. Catabolism is the process by which larger, more complex substances are broken down into smaller, simpler molecules. Catabolism releases energy. The complex molecules in foods are broken down into nutrients so the body can use them to assemble the structures and substances needed for life.

Taken together, these two processes are called metabolism. Metabolism is the sum of all anabolic and catabolic reactions that take place in the body. Both anabolism and catabolism occur simultaneously.

Movement

Human movement includes not only actions at the joints of the body, but also the motion of individual organs and even individual cells. Muscle cells contract and relax to maintain the body's posture. The body coordinates the action of entire muscle groups to enable the movement of air in and out of the lungs, to push blood throughout the body, and to propel the food eaten through the digestive tract.

Development, Growth and Reproduction

Development is all of the changes the body goes through in life. The development also includes the processes of growth and repair, both of which involve cell differentiation — transition of a cell from one cell type to another. Growth is the increase in body size. Like all multicellular organisms, humans grow by increasing the number of existing cells, increasing the amount of non-cellular material around cells (such as mineral deposits in bone), and, within very narrow limits, increasing the size of existing cells. Reproduction is a fundamental function of human life that allows for the continuation of the species. Reproduction involves the production of offspring through sexual or asexual means. In humans, reproduction occurs through sexual reproduction, which involves the fusion of male and female gametes to form a zygote. The zygote then undergoes a series of developmental processes to form an embryo, which eventually develops into a fetus and is born as a baby.

This text is adapted from Openstax, Anatomy and Physiology 2e, Section 1.3 Functions of Human Life