1. Transport across the CSM

2. CSM transport
Phospholipid bilayer creates effective barrier against water soluble molecules and ions
Prevents aqueous contents from escaping
Some essential transport is achieved through diffusion, facilitated diffusion, osmosis, active transport and bulk transport

3. Diffusion
Diffusion: net movement, as a result of random motion of its molecules or ions, of a substance from a region of high concentration to a region of low concentration
Particles move down a concentration gradient

4. Rates of Diffusion
‘steepness’ of concentration gradient: greater difference = higher rate
Temperature: higher temperature = higher rate
Surface area of diffusion: greater surface area – higher rate
Nature of molecules/ions: small molecules = greater rate

5. Diffusion
Respiratory gases cross membrane by diffusion (uncharged and nonpolar)
Water (even though it is polar) can cross because molecules are very small

6. Facilitated diffusion
Diffusion that takes place with the help of a certain protein molecule
Channel proteins
Carrier proteins

7. Channel proteins Water-filled pores Fixed shape
Allow charged substances (usually ions) to diffuse through membrane
Gated to allow for selectivity and control of movement

8. Carrier proteins
Flips between shapes to alternately open binding sites on interior/exterior of membrane
Direction of movement depends on concentration gradient inside and outside of cell

10. Osmosis
Type of diffusion involving water molecules only

11. Water potential
Water potential: tendency of water molecules to move from one place to another
Measured by Greek symbol psi Ψ

12. Water potential Water potential for pure water is 0
Solutes make water potential less than 0, the more solute, the more negative the water potential
The amount that solutes lower the water potential is called solute potential

13. Pressure potential Increasing pressure increases water potential
The contribution made by pressure to water potential is called pressure potential and is given by symbol Ψp
Pressure potential makes water potential less negative (more positive)

14. Water potential in animal cells

15. Osmosis in plant cells

16. Active Transport
Active transport moves molecules/ions against concentration gradient
Achieved by carrier proteins (specific for structure of particular ion/molecule)
Requires ATP for energy, supplied by cellular respiration
Can occur into or out of the cell

17. Sodium-potassium pump
Found in CSM of all animal cells
Use ~30% avg cell energy and ~70% neuron cell energy
Pump 3 Na+ ions out of the cell and 2 K+ ions into the cell
Net result: inside of cell become more negative than the outside

18. Sodium-potassium pump
Difference in charges between inside membrane and outside creates a potential difference (p.d.) which allows nerve cells to propagate a signal

19. Active transport
Important in re-absorption in the kidneys, where certain useful molecules and ions have to be re-absorbed into the blood after filtration into the kidney tubules
Involved in
absorption of
products of
digestion in the
gut

20. Active transport
Used to load sugar from photosynthesizing cells of leaves into phloem tissue for transport around the plant

21. Active transport

22. Bulk transport
Bulk transport involves the mechanism of moving large quantities of molecules into the cell (endocytosis) or out of the cell (exocytosis)
Large molecules such as proteins or polysaccharides, part of cells, or even whole cells may be transported across the membrane

23. Endocytosis
Involves the engulfing of material by the CSM to form a small sac, or endocytic vacuole
Two forms: phagocytosis and pinocytosis

24. phagocytosis ‘cell eating’ Bulk up take of solid material
Cells specializing in this are called phagocytes and the vacuoles are called phagocytic vacuoles
Ex: engulfing of bacteria by immune cells

25. endocytosis

26. Pinocytosis ‘cell drinking’ – bulk uptake of liquid into cell
Vacuoles ( vesicles) formed are often extremely small, in which the process is called micro-pinocytosis
Human egg cells take up nutrients from cells that surround it by pinocytosis

27. exocytosis Process by which bulk material is removed from a cell
Ex: how plants transport materials out of CSM to make cell wall
Ex: secretion of digestive enzymes of the pancreas
Secretory vesicle from the Golgi carry the enzymes to the CSM and release their contents

28. Bulk transport

29. Homework
Pg 81 #5,6,7 (ING Pg 34)