The modern cell theory states the following:

  1. All organisms are made up of cells.
  2. The cell is the basic unit of structure and function in living organisms.
  3. All cells come from other cells by cell reproduction.
  4. Cells contain hereditary information, which is passed from cell to cell during cell division.
  5. All cells are the same in chemical composition.
  6. All energy flow (metabolism and biochemistry) of life occurs within the cell.

In this section, you will look more closely at the second and sixth statements of the cell theory.

You have learned the levels of organization in living things. You know that cells make up tissues, tissues make up organs, organs make up organ systems, and organ systems make up an organism.

You have also learned the functions of the various organ systems in the human body.

Primary Function
Circulatory transports nutrients and oxygen to the body
Respiratory exchange of oxygen and carbon dioxide
Skeletal provides structure and protection
Muscular movement
Integumentary protection
Digestive breaks down food to provide energy and nutrients
Excretory gets rid of body waste
Reproductive produces offspring
Nervous coordinates the body
Endocrine regulates the body

Without cells, none of the tasks in the table above could be carried out. Cells carry out the basic functions of organisms, such as extracting energy from food and waste removal.

A cell is the smallest unit that can carry on all of the processes of life.

The function of a cell is to:

Source: Balance Beam, Selma, Clker

The main function of an organism is to maintain homeostasis. All the components of an organism, from the cell organelles to the organ systems, interact to maintain homeostasis or a balanced internal environment.