Cytology Osmosis and Water relations

1. Cytology Osmosis and Water relations

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

3. (a) 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) Equilibrium Net diffusion Net diffusion • Diffusion • Is the tendency for molecules of any substance to spread out evenly into the available space

4. (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. Equilibrium Net diffusion Net diffusion Net diffusion Equilibrium Net diffusion Figure 7.11 B • Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another

5. Osmosis is the a special form of diffusion in which of water molecules diffuse through a selectively permeable membrane. Net water movementoccurs 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 concentration gradient / water potential gradient

7. Why osmosis is relevant to living cell?

8. Why osmosis is relevant to living cell? • a selectively permeable membrane • a concentration gradient / water potential gradient

9. Water Balance of Cells Without Walls • Tonicity /concentration strength of a solution: 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 same as it is inside the cell • There will be no net movement of water • If a solution is hypertonic • 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 less than it is inside the cell • The cell will gain water

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

17. RBC and osmosis • https://www.youtube.com/watch?v=A8cI6FkcG4c https://www.youtube.com/watch?v=OYoaLzobQmk

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

19. Plant cell_effect of a rigid cell wall

20. A pressure component The water column will stoprising at a certain level, why?

21. Water movement and water potential

22. Components of Water potential

23. Components of Water potential

24. Components of Water potential Pressure potential: hydrostatic pressure affects water potential

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

26. Water purification with reverse osmosis

27. Singapore reclaimed water by ‘reverseOsmosis’

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

29. A turgid cell: Cell membrane pressingon the cell wall

30. Turgor pressure Expandingcell 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

31. Turgidity in plant cell a) Water enters the cell by osmosis 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

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

33. Water balance in cells with rigid cell walls

34. Rhoeo Discolor epidermis

35. Rhoeo Discolor epidermisplasmolysed cell

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

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

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