Diffusion and osmosis

1. Diffusion and osmosis B M Subramanya Swamy M.Sc. B.Ed. CIE Co ordinator & Examination Officer Kanaan Global School Jakarta Indonesia [email protected]

2. Diffusion and osmosis Crossing the cell membrane Diffusion Osmosis Active transport

3. Crossing the cell membrane Substances can cross the membrane because of the membrane’s property of being partially permeable That is it is permeable to some substances and not to others Some substances are able to move into the cell and some are allowed out

4. Methods of crossing the cell membrane Crossing the membrane by Method Active transport Movement of substances from a region of lower concentration to a region of higher concentration Against the concentration gradient Requires energy from cell respiration Passive transport Movement of substances from a region of higher concentration to a region of lower concentration Not against a concentration gradient Does not require energy

5. Diffusion Movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient Form of passive transport Diffusion stops when the concentration gradient is zero that is state of equilibrium is reached

6. Importance of diffusion Importance Activity Gaseous exchange during respiration & photosynthesis Plant and animal cells use oxygen during aerobic respiration During photosynthesis carbon di oxide diffuses into the plants and oxygen diffuses out Excretion of waste products Waste products diffuse out of tissue It is transported to excretory organ by the circulatory system Absorption of digested food Digested products diffuse into the blood stream Excess mineral salts and vitamins are removed from blood stream by diffusion

7. Factors affecting rates of diffusion Rate of diffusion Effect Temperature Increase temp increase rate of diffusion Size of particles Decrease molecule size increase rate of diffusion Thickness of barrier Cell membrane in plant and animals are about the same Increase thicker cell wall decrease rate of diffusion Concentration gradient Increase concentration gradient increase rate of diffusion Total surface area of cell membrane Increase in surface area increase rate of diffusion E.g. root hair cells microvillus in ileum

8. Osmosis Definition Net diffusion of water across a selectively permeable membrane from one solution to another of lower water potential Movement involves water molecules

9. Water potential Measure of whether it is likely to lose or gain water molecules from another solution Distilled water has the highest possible water potential The difference between potential of two solution creates a water potential gradient

10. Reaction of the cells in different types of solution Types of solution Concentration as compared to cell sap Movement of water in the cell Hypotonic More dilute than cell sap Higher water potential than cell Water flows into the cell Cell become turgid Isotonic Same concentration as cell sap Zero water potential No net flow of water Cell becomes flaccid Hypertonic solution Concentration of solutes is higher outside the cell Lower water potential than cell Water flows out of the cell Cell becomes Plasmolysed

11. Effect of osmosis in plant cell Hypotonic solution (placed in pure water) Cell become turgid Cytoplasm is pressed against the wall Cell is prevented from bursting by the cell wall Isotonic solution Cell unchanged Hypertonic solution (placed in concentrated salt solution ) Cell is plasmolysed Cytoplasm shrinks

12. Effect of osmosis in animal cell Hypotonic solution (placed in pure water) Cell swells Finally bursts( hemolysed ) Isotonic solution Cell unchanged Hypertonic solution (placed in concentrated salt solution ) Cell shrinks Becomes wrinkled( crenated )

13. Active transport Movement of particles(molecules & ions) through a membrane from region of low concentration to region of high concentration Against a concentration gradient Energy consuming ;uses oxygen from aerobic respiration to produce energy Increase the speed of ions /substances moving into cell when diffusion isn’t fast enough E.g. plants absorb mineral salts present as charged ions in soil . The concentration of ions in soil is less than vacuole therefore uptake of ions is assisted by active transport across the root hair