Section 3: From Cell to Organism

1. Section 3: From Cell to Organism Preview • Key Ideas • Diversity in Cells • Levels of Organization • Body Types • Summary

2. Key Ideas • What makes cells and organisms different? • How are cells organized in a complex multicellular organism? • What makes an organism truly multicellular?

3. Diversity in Cells • Both prokaryotic and eukaryotic cells can have a variety of shapes and structures. • The function of a cell is determined by its shape and the organelles found in the cell. • The different organelles and features of cells enable organisms to function in unique ways in different environments.

4. Diversity in Cells, continued Diversity in Prokaryotes • Many prokaryotes have a flagellum, a long, hair-like structure that grows out of the cell and enables the cell to move quickly through its environment. • Prokaryotes may also have pili, short outgrowths that allow the cell to attach to surfaces or other cells.

5. Flagella On Prokaryotic Cells Click to animate the image. B C D A E F

6. Diversity in Cells, continued Eukaryotic Cell Specialization • Depending on their function, eukaryotic cells can also vary in their internal organelles. For example, muscle cells, which use large amounts of energy, contain many mitochondria. • Animal and plant cells are two types of eukaryotic cells. Both have many of the same organelles, but plant cells also have chloroplasts, a large central vacuole, and a cell wall.

7. Eukaryotic Cells Click to animate the image. I K H C A G D J M B D L C E J B A F I H E G F

8. Levels of Organization • A tissue is a distinct group of similar cells that perform a common function. • An organ is a collection of tissues that work together to form a structure which performs a specific function. • An organ system is composed of a group of organs that work together to perform major body functions.

9. Organization in Multicellular Organisms Click to animate the image.

10. Body Types • Unicellular organisms can thrive independently or live together in groups. • Cells that are permanently associated but do not work together or integrate cell activities are called colonial organisms. • A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other. True multicellularity occurs only in eukaryotes.

11. Visual Concept: Comparing Organisms that are Unicellular and Multicellular

12. Body Types, continued • In a multicellular body, cells are interdependent. Distinct types of cells have specialized functions to help the organism survive. • The individual cells in a multicellular organism cannot survive alone and are dependent on the other cells of the organism. • Must multicellular organisms begin as a single cell, which divides to form more cells. These cells then grow and become specialized in a process called differentiation.

13. Visual Concept: Differentiation

14. Summary • The different organelles and features of cells enable organisms to function in unique ways in different environments. • Plants and animals have many highly specialized cells that are arranged into tissues, organs, and organ systems. • A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other.