1. Transport Across the Cell Membrane maintains homeostasis of cell membrane is selectively permeable – some things can pass through but others can’t 3 types: active transport, passive transport, and bulk transport

2. 1. Passive Transport passive = no energy req’d move through membrane due to differences in concentration gradient 3 different types

3. 1. Diffusion Movement of molecules from an area of high concentration to an area of low concentration across a concentration gradient Used transport small molecules like CO 2 H 2 O, and O 2 Animation: How Diffusion Works

4. 2. Osmosis waterDiffusion of water from a region of high concentration to a region of low concentration Water can diffuse into or out of a cell, it depends on the concentration on either side of the cell membrane Animation: How Osmosis Works

5. Water potentials Water moves from a place with a LESS NEGATIVE (higher) water potential to a place with a MORE NEGATIVE (lower) water potential The water potential of pure water is 0 (zero). Solutions have negative water potentials – the more concentrated the solution, the more negative the water potential.

6. 3 Types of Osmosis 1.Hypotonic contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.

7. 2. Hypertonic contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). when cell is placed in a hypertonic solution, water diffuses out of the cell, causing the cell to shrivel.

8. 3. Isotonic contain the same concentration of solute as an another solution (e.g. the cell's cytoplasm). when cell placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. fluid that surrounds the body cells is isotonic.

9. http://www.zerobio.com/flashmx/transport.swf

10. 3.Facilitated diffusion

11. Key features how glucose/charged ions moves into cells passive – does not require energy uses carrier proteins solute molecules “combine” with carrier proteins in the membrane. carrier molecules speed (or facilitate) the passage of the solute molecules across the membrane.

12. Spot the difference!

13. 2 kinds of proteins involved: 1.CARRIER PROTEINS bind to a specific type of diffusing molecule. have a highly specific hydrophilic region to which the solute molecule binds. binding cause the protein to undergo a change in shape that moves the solute across the bilayer and release it on the other side

14. Carrier proteins Animation: How Facilitated Diffusion Works

15. Carrier proteins

16. 2. ION CHANNELS formed by proteins with a central pore that is lined with charged groups. help the diffusion of charged particles such as Ca 2+, Na +, K +, HCO 3- and Cl ions. Some channels are gated and allow cells to regulate the flow of ions from one cell to another.

17. Ion channel

18. Factors affecting Rate of Diffusion 1.Concentration Difference happens ONLY when a concentration gradient is present and solute travels ALONG (down) a concentration gradient 2. Saturation there are only a limited number of carrier molecules per unit area of membrane. rate of movement reaches a max. when all carrier molecules are fully loaded with solute molecules

19. 2. Active Transport the transport of molecules or ions across a membrane by carrier proteins against a concentration gradient.

20. requires energy involves carrier proteins in the membrane. hydrolysis of ATP releases the energy required for active transport. Cells involved in active transport have a large number of mitochondria to provide the ATP required

21. Spot the difference

23. Sodium-Potassium Pump ex. of active transport Exists in most cell membranes. Actively removes sodium ions from the cell while actively accumulating potassium ions into them from their surroundings Animation: How the Sodium Potassium Pump WorksAnimation: How the Sodium Potassium Pump Works

25. 3. Bulk Transport used for materials to large to enter via passive or active transport vesicles created by folding of cell membrane onto itself to either engulf or expel materials 2 types: endocytosis & exocytosis

27. Endocytosis the transport of large particles into the cell in vesicles formed by folding in of the cell surface membrane 3 types: 1.Pinocytosis (cell drinking) intake of small droplet of extracellular fluid along with solute particles occurs in all cells often

28. 2. Phagocytosis (cell eating) intake of large droplet of extracellular fluid including particulate matter (bacteria or organic matter) occurs only in specialised cells like amoeba or macrophages (bacteria fighting immune cells) Animation: Phagocytosis

29. 3. Receptor-assisted endocytosis involves intake of specific molecules that attach to special protiens in cell membrane that serve as receptors have a unique shape that fit only to one specific molecule ex. animal cells use this to bring cholesterol into cell

31. Exocytosis the reverse process and is used to secrete proteins, e.g digestive enzymes, out of the cells. vesicle forms inside cell moves to membrane and empties contents outside of cell ex. pancreas secretes insulin