2. Learning Goal Understand that all living things are made of cells. Compare and contrast prokaryotic and eukaryotic cells.

3. What structures of a plant cell can you observe under a microscope? Investigation 15.1 Observing Cells

4. 15.1 Cells Your body is composed of billions of cells. You have nerve cells, skin cells, muscle cells, blood cells, and many other types as well.

5. Cell definition A cell is the basic unit of structure and function in an organism. All organisms are made of one or more cells.

6. Organisms and cells Unicellular organisms are made of only a single cell. Multicellular organisms are made of more than one cell. All animals and plants are multicellular organisms. All organisms are made of one or more cells.

7. Characteristics of cells Each cell in your body shares the characteristics of all living things.

8. Specialized body cells About 200 different types of specialized cells make up the tissues and organs of your body.

9. Shared characteristics 1. All cells are surrounded by a cell membrane. 2. All cells contain cytoplasm. 3. All cells reproduce using DNA.

10. Learning Goal If a cell does not have a nucleus, it is prokaryotic. If a cell has a nucleus, it is eukaryotic.

11. Classifying cells Bacteria have prokaryotic cells and are called prokaryotes. Prokaryotic cells do not have a nucleus. Scientists believe that all life on Earth came from these cells.

13. Classifying cells Eukaryotic cells have a nucleus and membrane-covered organelles. They tend to be about ten times larger than prokaryotic cells. Animals, plants, fungi, and protists all have eukaryotic cells.

15. Autotrophs Autotrophs are organisms that can make their own food. Some autotrophs, such as plants and algae, make their own food through a process called photosynthesis.

16. Heterotrophs Heterotrophs are organisms that cannot make their own food. A heterotroph must obtain its energy from the molecules originally made by autotrophs.

17. Cell reproduction The formation of new organisms of the same species is called reproduction. Reproduction is an important life function. There are two types: –asexual reproduction –sexual reproduction

18. Types of reproduction Asexual reproduction is reproduction that requires only one parent. Most unicellular organisms reproduce this way. Sexual reproduction involves two parents. Most multicellular organisms reproduce this way.

19. Food for thought Why does a more advanced cell have a nucleus? Are you a prokaryotic organism or an eukaryotic organism?