1. Cells, Tissues, Organs, Organ Systems and Organism
Body Organization
Cells, Tissues, Organs, Organ Systems and Organism

2. Level One: Cells
A cell is a basic unit of structure and function in a living thing.
The human body contains about 100 trillion cells.
Cells can not be seen without a microscope.
Three important structures to recall are cell membrane, nucleus, and cytoplasm.
What is the function of the nucleus?

3. Functions of Cell Structures
Cell membrane: forms the outside boundary of the cell; materials move across the cell’s membranes
Nucleus: the control center that directs the cell’s activities and contains information that determines the cell’s characteristics
Cytoplasm: a clear, jellylike substance in which many important cell structures are found

4. Level Two: Tissues
A tissue is a group of similar cells that perform the same function.
The human body contains 4 basic types of tissue:
muscle tissue
nerve tissue
connective tissue
epithelial tissue

5. Muscle Tissue
Like the muscle cells that form it, muscle tissue can contract or shorten.
One kind of muscle tissue allows the body to move.
Other kinds of muscle tissue move:
1. blood through the heart
2. food through the digestive system

6. Nerve Tissue Nerve tissue directs and controls movement.
Nerve tissue carries messages back and forth between the brain and every other part of the body.
Nerve tissue enables you to see, hear, and think.
Your brain, spinal cord and nerves consist of nerve tissue.
Under a microscope you can see the neurons & glial cells.

7. Epithelial Tissue
Epithelial tissue covers the surfaces of your body and the outside of your internal organs.
Under a microscope epithelial tissue looks like it is packed tight together & in sheets or layers.
Your skin is composed of 2 layers of epithelial tissue, the epidermis and dermis. It is also composed of connective, nerve & muscle tissue.

8. Connective Tissue
Connective tissue provides support for your body and connects all its parts.
Examples of connective tissue are:
bones & tendons-for support
fat-provides insulation from cold & stores
energy
blood-travels to all parts of your body
Under a microscope connective tissue looks like fibrous strands of protein collagen

9. Organs
An organ is a structure that is composed of different kinds of tissue. It performs a specific job.
For example, the heart pumps blood throughout the body
An interesting fact about the heart: it contains all 4 kinds of tissue! So does the skin!

10. Organ Systems
An organ system is a group of organs that work together to perform a major function.
11 systems make up the human body:
Circulatory Nervous
Digestive Reproductive
Endocrine Respiratory
Excretory Skeletal
Immune Integumentary (Skin)
Muscular

11. Thinking Critically Answer the following questions:
What systems of the body are involved when you prepare a sandwich and then eat it?
Which 2 systems work together to get oxygen to your cells?