KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

1. KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.

2. cell membrane The cell membrane has two major functions. • forms a boundary between outside and inside of the cell. outside cell inside cell

3. cell membrane The cell membrane has two major functions. • forms a boundary between inside and outside of the cell • controls passage of materials outside cell inside cell

4. Phospholipid – is a molecule composed of three parts: Head – forms hydrogen bonds with water. • A charged phophate group---polar • Glycerol-----polar Tail • Two fatty acids---nonpolar

5. Cell membranes are composed of two phospholipid layers.

6. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer.

7. carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane.

8. carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane. • The fluid mosaic model describes the membrane.

9. carbohydrate chain protein cell membrane cholesterol protein protein channel The Fluid Mosaic Model • The fluid mosaic model describes the describes the arrangement of molecules that make up the cell membrane. • Gives flexibility • Imbedded with many proteins and protein channels to assist in molecules leaving and entering the cell. • Cholesterol provides support

10. The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

11. The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.

12. Chemical signals are transmitted across the cell membrane. • Receptor- a protein that detects a signal molecule and performs an action in response. • It recognizes and binds to only certain molecules (enzyme) • Receptors bind with ligands and change shape. • There are two types of receptors. • Intracellular receptor - Membrane receptor

13. Chemical signals are transmitted across the cell membrane. - Intracellular receptor – Located inside the cell. Bound by molecules that can cross the membrane.

14. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • Membrane receptor – bind to molecules that cannot enter the cell. When bound the receptor transmits the signal inside the cell by changing shape.

15. 3.4 Diffusion and Osmosis KEY CONCEPT Materials move across membranes because of concentration differences.

16. 3.4 Diffusion and Osmosis • Passive transport - is the movement of molecules • across the cell membrane that does not require energy • input from a cell. • There are two types of passive transport. • diffusion • osmosis

17. 3.4 Diffusion and Osmosis • Molecules diffuse down a concentration gradient- which is the difference in the concentration of a substance from one location to another. • Diffusion – is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration. • Osmosis – is the movement of • water across a semi-permeable • membrane from an area of higher • water concentration to an area of • lower water concentration.

18. 3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. • Osmosis is the diffusion of water molecules across a semipermeable membrane.

19. 3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. • There are three types of solutions. • isotonic • hypertonic • hypotonic

20. 3.4 Diffusion and Osmosis Some molecules can only diffuse through transport proteins. • Some molecules cannot easily diffuse across the cell membrane. • Facilitated diffusion is diffusion through transport proteins.

21. 3.5 Active Transport, Endocytosis, and Exocytosis KEY CONCEPT Cells use energy to transport materials that cannot diffuse across a membrane.

22. 3.5 Active Transport, Endocytosis, and Exocytosis Active transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient. • Passive transport requires no energy from the cell. • Active transport is powered by chemical energy (ATP). • Active transport occurs through transport protein pumps. • Cells use active transport to maintain homeostasis.

23. 3.5 Active Transport, Endocytosis, and Exocytosis A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis. • Cells use energy to transport material in vesicles. • Endocytosis is the process of taking material into the cell. • Phagocytosis is a type of endocytosis.

24. 3.5 Active Transport, Endocytosis, and Exocytosis A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis. • Cells use energy to transport material in vesicles. • Exocytosis is the process of expelling material from the cell.