1. Cell Boundaries 7.3

2. Cell Membrane Thin, flexible barrier around a cell; regulates what enters and leaves the cell.

3. Cell Wall Strong supporting layer around the cell membrane in plants, algae, and some bacteria.

4. Lipid Bilayer Double-layered sheet that forms the core of nearly all cell membranes.

5. Concentration The mass of solute in a given volume of solution, or the mass/volume.

6. Diffusion Process by which molecules tend to move from an area where they are more concentrated to an area where they less concentrated.

7. Equilibrium When the concentration of a solute is the same throughout a solution.

8. Osmosis Diffusion of water through a selectively permeable membrane.

9. Isotonic When the concentration of two solutions is the same.

10. Hypertonic When comparing two solutions, the solution with the greater concentrations of solutes.

11. Hypotonic When comparing two solutions, the solution with the lesser concentration of solutes.

12. Facilitated Diffusion Movement of specific molecules across cell membranes through protein channels.

13. Active Transport Energy-requiring process that moves material across a cell membrane against a concentration difference.

14. Endocytosis Process by which a cell takes material into the cell by infolding of the cell membrane.

15. Phagocytosis Process in which extensions of cytoplasm surround and engulf large particles and take them into the cell.

16. Pinocytosis Process in which a cell takes in liquid from the surrounding environment.

17. Exocytosis Process by which a cell releases large amounts of material.

18. Key Concept What are the main functions of the cell membrane and the cell wall? The cell membrane regulates what enters and leaves the cell and also provides protection and support. The main function of the cell wall is to provide support and protection for the cell.

19. Key Concept What happens during diffusion? Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy.

20. Key Concept What is osmosis? It is the diffusion of water through a selectively permeable membrane.