You are already familiar with the cell—the smallest structural and functional unit of a living organism. Each cell can perform all the basic activities required for life. Some organisms, like bacteria, are unicellular—an entire organism made of only one cell. These single-celled organisms rely on diffusion and osmosis to take in needed raw materials (like food and oxygen) and to release wastes (like carbon dioxide).
What happens when organisms become more complex? How do organisms built of billions, or even trillions of cells (like human beings), get the raw materials needed to each and every cell? The answer is body systems. Large, complex organisms need many levels of organization to ensure all cells get what they need to perform life functions.
Body system organization begins with the cell. Cells working together form tissues, tissues working together form organs, and organs working together form organ systems. For example, cardiac muscle cells group together to form cardiac muscle tissue, which in turn forms the heart. The heart pumps blood through the circulatory system, delivering needed materials (glucose, oxygen) and picking up waste (carbon dioxide) from cells all over the body.
Organs systems work together to efficiently and effectively provide all body cells with their basic needs to carry out life functions. You can think of the organs and systems as puzzle pieces. The whole animal is the picture on the puzzle. So, like anyone who assembles puzzles, let's look at the box to see the big picture first.
Directions: Watch Human Body Systems: The 11 Champions for a review of the human body systems and their functions.