1. Cytology Osmosis and Water relations

2. is the tendency of gaseous or aqueous particles to spread from a more concentrated region to a less concentrated region Diffusion is the tendency of gaseous or aqueous particles to spread from a more concentrated region to a less concentrated region

3. Diffusion Diffusion Is the tendency for molecules of any substance to spread out evenly into the available space Is the tendency for molecules of any substance to spread out evenly into the available space Diffusion of one solute. The membrane has pores large enough for molecules of dye to pass through. Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more molecules. The dye diffuses from where it is more concentrated to where it is less concentrated (called diffusing down a concentration gradient). This leads to a dynamic equilibrium: The solute molecules continue to cross the membrane, but at equal rates in both directions. Molecules of dye Membrane (cross section) Net diffusion Equilibrium (a)

4. Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another Figure 7.11 B Diffusion of two solutes. Solutions of two different dyes are separated by a membrane that is permeable to both. Each dye diffuses down its own concen- tration gradient. There will be a net diffusion of the purple dye toward the left, even though the total solute concentration was initially greater on the left side. (b) Net diffusion Equilibrium

5. Osmosis is the a special form of diffusion in which of water molecules diffuse through a selectively permeable membrane. Net water movement occurs from a dilute region (higher water potential) to a more concentrated region (lower water potential).

6. The two conditions for osmosis a selectively permeable membrane a selectively permeable membrane a concentration gradient / water potential gradient a concentration gradient / water potential gradient

7. Why osmosis is relevant to living cell? Why osmosis is relevant to living cell?

8. a selectively permeable membrane a concentration gradient / water potential gradient

9. Water Balance of Cells Without Walls Tonicity /concentration strength of a solution: Tonicity /concentration strength of a solution: Is the ability of a solution to cause a cell to water Is the ability of a solution to cause a cell to gain or lose water

10. If a solution is isotonic The concentration of solutes is the it is inside the cell The concentration of solutes is the same as it is inside the cell There will be of water There will be no net movement of water If a solution is hypertonic The concentration of solutes is The concentration of solutes is greater than it is inside the cell The cell will lose water If a solution is hypotonic The concentration of solutes is The concentration of solutes is less than it is inside the cell The cell will gain water

11. Water potential A measure of the of a solution to give out water molecules A measure of the capacity of a solution to give out water molecules Water moves from a region of higher water potential to a region of lower water potential has the highest water potential. The water potential of pure water at standard laboratory condition is assigned as = 0 Pure water has the highest water potential. The water potential of pure water at standard laboratory condition is assigned as = 0 ψ ψ

12. Components of Water potential Osmotic potential: Presence of solute lowers water potential

13. Solute particles decrease the ‘free energy’ of water molecules

14. Components of Water potential Osmotic potential: Solutes lowers water potential A more concentrated solution has a ________ water potential The osmotic potential of pure water is 0 All aqueous solutions have a ________ osmotic potential

15. What produces the osmotic strength of cells ? cytoplasm is a relatively concentrated solution of : sugar, mineral salts, amino acids, protein, ………and many other dissolved substances

16. Water Balance of Cells Walls Water Balance of Cells without Walls

17. Animals and other organisms without rigid cell walls living in hypertonic or hypotonic environments Must have special adaptations for Must have special adaptations for osmoregulation Paramecium has contractile vacuoles to remove excess water

18. Plant cell_effect of Plant cell_effect of a rigid cell wall

19. A pressure component The water column will stop rising at a certain level, why?

20. Water movement and water potential

21. Components of Water potential

23. Pressure potential: hydrostatic pressure affects water potential

24. Components of Water potential Reverse osmosis: Obtain pure water from salt water by applying positive pressure

25. Water purification with reverse osmosis

26. Water Balance of Cells with Water Balance of Cells with a rigid cell wall Cell walls Cell walls Help maintain water balance Help maintain water balance

27. A turgid cell: Cell membrane on the cell wall A turgid cell: Cell membrane pressing on the cell wall

28. Turgor pressure Expanding cell volume pushes outward on the cell wall – the pressure pushing on the cell wall Rigid cell wall pushes back on the cell membrane and prevent excessive expansion

29. Turgidity in plant cell a) Water enters the cell by osmosis turgor pressure b) Expansion of cell volume forcing the plasma membrane outwards against the cell wall. A pressure develops called the turgor pressure c) The outward pressure is matched by an inward pressure (wall pressure), equal in magnitude but opposite in direction

30. Turgidity and support These pressures provide mechanical to the plant tissue. If a plant experiences a lack of water the cell becomes plasmolysed, wall pressure is lost and the plant wilts These pressures provide mechanical support to the plant tissue. If a plant experiences a lack of water the cell becomes plasmolysed, wall pressure is lost and the plant wilts

31. Water balance in cells with Water balance in cells with rigid cell walls

32. Rhoeo Discolor epidermis

33. Rhoeo Discolor epidermis plasmolysed cell

35. If a plant cell is turgid If a plant cell is turgid It is in a hypotonic environment It is in a hypotonic environment It is very firm, a healthy state in most plants It is very firm, a healthy state in most plants

36. If a plant cell is flaccid If a plant cell is flaccid It is in an isotonic or hypertonic environment It is in an isotonic or hypertonic environment

37. Wilting can be reversed -- if water is replaced fast enough