The Organization of Organisms

Cells are often called “the basic unit of life”. What is meant by this is that cells are the smallest and simplest level at which all the functions necessary for life, growth, maintenance, and reproduction, can occur. Some organisms, such as many protistans, never develop beyond this level.

Cells with a similar structure and function are referred to as tissues, which allow for cells to function together to benefit the whole organism. The functions of tissues are varied. Some functions include carrying oxygen to other tissues (blood), protecting other tissues (stratified squamous epithelium), and carrying electrical impulses to other tissues (nervous tissue). Tissues allow for organisms to have larger, more complicated body plans.

Various tissues constitute an organ, such as the stomach, kidney, and lung. The many tissues of organs work together to fulfill a larger function for the organism. For instance, in the stomach there is a tissue which secretes digestive acid, another tissue which secretes mucous, and a muscular tissue which churns the stomach. These tissues work together to allow the organism to chemically digest its food while protecting its other tissues from the extreme acidity.

Many organs come together to form an organ system, which fulfill a major role, perhaps more than one, for the organism. Organ systems include the circulatory system, the digestive system, and the respiratory system. In the case of the digestive system, its major role is for obtaining, digesting, and excreting food and waste. We can follow the digestive tract easily and see the many organs involved in the system, such as the stomach, small intestine, liver, and large intestine.

All of the organ systems combined make up an individual. Many individuals of the same species in the same area make up a population. All of the populations in the same area make up a community or ecosystem. All of the ecosystems on Earth make up the biosphere. This is the organization of organisms from cell to biosphere.