1. Studying Life 1.3

2. Biology Science that seeks to understand the living world.

3. Cell Collection of living matter enclosed by a barrier that separates the cell from its surroundings; basic unit of all forms of life.

4. Homeostasis Process by which organisms maintain a relatively stable internal environment.

5. Sexual Reproduction Process by which cells from two different parents unite to produce the first cell of a new organism.

6. Asexual Reproduction Process by which a single parent reproduces by itself.

7. Metabolism Set of chemical reactions through which an organism builds up or breaks down materials as it carries out its life processes.

8. Stimulus A signal to which an organism responds.

9. Key Concept What are some characteristics of the living things? Living things share the following characteristics: Made up of units called cells Reproduce Based on a universal genetic code Grow and develop Obtain and use materials and energy Respond to their environment Maintain a stable internal environment Taken as a group, living things change over time

10. Key Concept How can life be studied at different levels? Some of the levels at which life can be studied include molecules, cells, organisms, populations of a single kind of organism, communities of different organisms in an area, and the biosphere. At all these levels, smaller living systems are found within larger systems.