1. Cells: The Building Blocks of Life Section 1-1 What is Life?

2. The Six Characteristics of Living Things

3. All living things can be called organisms.

4. Cellular Organization All organisms are made of small building blocks called cells. A cell is the basic unit of structure and function in an organism.

5. Some organisms are unicellular, like bacteria. Some organisms are multicellular, like animals.

6. The Chemicals of Life Water is the most abundant chemical found in living cells. Proteins and lipids (fats) are used as the building materials of cells. Genetic material is composed of nucleic acids, another important building material.

7. Energy Use All living things must undergo metabolism to make energy to stay alive.

8. Growth and Development Growth is the process of becoming larger. Development is the process of change that occurs during an organism’s life to produce a more complex organism.

9. Response to Surroundings A change in an organism’s surroundings that causes the organism to react is called a stimulus (plural stimuli).

10. Response to Surroundings An organism reacts to a stimulus with a response—an action or change in behavior. A plant growing toward light is an example of a response.

11. Reproduction All living things reproduce offspring similar to themselves.

12. Life Comes From Life The mistaken idea that living things arise from nonliving sources is called spontaneous generation. The experiments of Redi and Pasteur helped to demonstrate that organisms do not arise from nonliving material.

13. The Needs of Living Things energy water living space stable internal conditions

14. Energy All living things must have a source of energy. Food is used as the energy source. The source of food for most autotrophs is the sun. Heterotrophs eat other organisms to acquire food.

15. Water All living things need water to survive.

16. Living Space All organisms need a place to live—a place to get food and water and find shelter. Some organisms may compete for space.

17. Stable Internal Conditions Homeostasis refers to an organism's ability to maintain stable internal conditions.