2. Levels of Organization

3. Division of Labor & The First Level Within multi-cellular organisms there is division of labor. Division of labor means that the work (labor) of keeping the organism alive is divided (division) among the different parts of the body. Each part has a specific job to do and as each part does its special job, it works in harmony with all the other parts. The arrangement of specialized parts within a living thing is sometimes referred to as levels of organization. Cells are the first level of organization.

4. Cells: LOTS of Different Kinds! Here are two examples. Can you guess what kind? Nerve CellsSkin Cells

5. Second Level: Tissues There are four basic/major types of tissues in the human body: Muscle tissueNerve tissue Connective tissue Epithelial tissue (There are other kinds of tissues besides these.) Other kinds of tissue include bone tissue (a strong solid tissue that gives you shape and support) made of bone cells in your body form bone tissue. Blood cells in your body are part of blood tissue, a liquid tissue responsible for transporting food and oxygen throughout the body. In any multi-cellular organism, cells rarely work alone. Cells that are similar in structure and function are usually joined together to form tissues.

6. Let’s Look Again… Here are the cells we saw before, but if you look closely, you can see that they all look similar. Nerve cells working together make nerve tissue, and skin cells make up a special type of epithelial tissue.

7. Level Three: Organs When a bunch of different types of tissues work together, they form an organ. There are many organs in the body. How many can you name??

8. Level Four: Organ Systems A group of organs that work together to perform a major function is an organ system. For example, your heart is part of your circulatory system, which carries oxygen and other materials throughout your body. Besides the heart, blood vessels are organs that work in your circulatory system.

9. The nervous system detects and interprets information from the environment outside the body and from within the body; controls most body functions. The immune system fights disease. The excretory system removes wastes. The endocrine system controls many body processes by means of chemicals, like hormones.

10. The muscular system enables the body to move; moves food through the digestive system, and keeps the heart beating. The skeletal system supports and protects the body, and works with the muscular system to allow movement; makes and stores blood cells and stores some other materials.

11. The digestive system takes food into the body, breaks the food down into smaller particles, and absorbs the digested materials. The respiratory system takes oxygen into the body and eliminates carbon dioxide. The reproductive system produces sex cells that can unite with other sex cells to create offspring; controls male and female characteristics.

12. Level 5 - Organism When all the systems work together to make a living thing (an organism). Organisms can be one cell big (amoeba, bacteria) or more (human, ant, frog) In a multicellular organism, each cell must carry out all the basic life functions and do their specific job to keep the organism alive.

13. Let’s Review…. 1 st Level: Cells working together form 4 th Level: Organ Systems, which work together to form 2 nd Level: Tissues, which can form 3 rd Level: Organs, which work together to form 5 th Level: Organisms!