1. Organization of Living Things
Section 4.3

2. What do we know? Which one of your body systems is the most important?
Why do you think scientists use the word system to describe your skeleton or your digestive system?
Can you think of an activity you do that requires different parts of your body to work together?

3. A Question of Scale
Make a list of the life activities of a pond organism that can only be seen under a microscope, such as an amoeba.
Make a second list of the life activities of a fish.
Compare the two lists.
Which organism do you think can adapt to a wider range of conditions? Why?

4. Organisms
Humans are considered many-celled organisms (we are made up of trillions of cells)
But other organisms are made up of only one cell (for example an amoeba)
To see most single-celled organisms, you need a microscope.
A many-celled organism carries out more complex activities than a single-celled organism.
Many-celled organisms have specialized cells to perform different tasks.
However, these cells must be organized so they can work together.

5. Levels of Organization
There are 5 main levels of organization:
Cells
Tissues
Organs
Organ Systems
Organism

6. Cells, Tissues, & Organs
Most many-celled organisms have specialized cells
Specialized- different cells that do different kinds of work.
Each type of specialized cells are organized into tissues
Where each kind of tissue performs a certain function.
Tissues are then organized into groups called organs.
Organ- group of tissues that work together to perform special functions.
Both plants and animals have tissues and organs.

7. Organ Systems
A group of organs that work together make up an organ system.
Some organisms have no organ systems (sponges)
Others have a few organ systems (flatworms)
More complex organisms have ten organ systems (dogs and humans)

8. Organisms Highest level of cellular organization is the organism.
All organisms carry out life processes.
The different organ systems work together to keep the organism alive.
Respiratory system- enables you to breathe
Muscular & Skeletal system- enable you to support, protect, and move your body.
Digestive system- enables you to process the nutrients your body needs to work properly.

9. What do you think?
Look at the illustrations on page 86 and 87 in your book:
Which picture shows cells most clearly?
What do you think the term cardiac means?
What system is shown in the picture of the runner?
What tissues make up the circulatory system?
What are the names of different types of blood vessels?

10. What have we learned?
List at least one example of each of the following: cell, tissue, organ, organ system, and organism.
Describe the difference between a cardiac muscle cell, cardiac muscle tissue, and the heart.
Can a single-celled organism contain tissue? Explain.
Classify the following as a tissue, organ, or system:
Brain, spinal cord, and nerves
Heart
Group of muscle cells