diffusion and osmosis
TRANSCRIPT
Ministry of Higher Education
and Scientific Research
Tishk International University
Faculty of Education
Department of Biology
Lab. 3
4th Grade (2021 –
2022)
Diffusion and Osmosis
By: Zanyar Othman
Objectives :
• What is the diffusion mainly in the plants ?
• The factors which affects diffusion.
• What is the osmosis process in the plants?
• The role of osmosis in the plants.
• Solute molecules moving from an areaof high concentration to an area oflow concentration
– Movement is based on kineticenergy (speed), charge, andmass of molecules
– Equilibrium is reached when there isan even distribution of solutemolecules
Diffusion
Factors affecting the diffusion rate:
1. Size and molecular weight of the particle: At a given temperature, a smaller particle (molecule) moves faster than a larger one.
2. Temperature: As the temperature increases, the amount of energy available for diffusion is increased. This means that a given particle will move faster at a higher temperature.
3. Concentration Difference: The greater the concentration difference between the two compartments will lead to a faster diffusion rate.
4. Diffusion Distance: the short distance leads to faster diffusion of particles, and the long distance leads to slower diffusion.
5. Surface Area: the larger surface area, leads to the greater rate of diffusion.
6. Permeability: The more permeable substance can diffuse faster.
Experiment (1): Diffusion of liquids in liquids (with temperature effect):
Concept: The rate of diffusion of food color (or dye) molecules is increased when temperature is increased. Temperature is a measure of molecular motion.Materials: 2 petri dishesFood color (or dye)Boiled water Ice waterProcedure:Pour a little boiled water into one petri dish (about an inch full); pour a little ice cold water, but no ice into the other. Set both on an overhead projector. Put a drop of food color into each dish. Observe Food color (or dye) spreads out more quickly through a bowl of warm water than it does through a bowl of cold water.
Experiment (2): The effect of size of particles on the diffusion rate.1. Add several drops of iodine solution 2% to boiled agar and pour it in to a test tube,
marked it (1).2. Add several drops of starch solution 2%to a boiled agar, and pour it to a second test tube
(2).3. Put the tubes in refrigerator to become solid.4. Add 1ml of starch solution (starch particles cannot pass the gelatin membrane) to the
first test tube, and 1ml of iodine solution (can pass the gelatin membrane) to the second one.
5. Observe the changes in the color of gelatin in the two test tubes.Note: The starch particles have a larger size as compared with iodine.Iodine + starch = blue-purple complex.
Osmosis
• Diffusion of water through a semi- permeable membrane
–
Semi-permeable: permeable tosolvents (WATER), but not tolarge molecules
– High [water] to low [water]
• Phospholipid
• Aquaporin
Types of osmosis in plant
1. Endo osmosis: When a plant cell is placed in much diluted solution, water or solvent molecules enter into the cell through plasma membrane (diffusion and bulk flow) from the outer medium, it is called endo osmosis.
1. Exo osmosis: When a plant cell is placed in concentrated solution, the water molecules move from cell into the outer concentrated medium through plasma membrane (diffusion and bulk flow) it is called exo osmosis.
Effect of Water on Cells
• Hypertonic Environment
– High [solute], low[water]
• Hypotonic Environment
– High [water], low [solute]
• Isotonic Environment
– [water] = [solute]
Plasmolysis: is the process of contraction or shrinkage of the protoplasm of a plant cell and is caused
due to the loss of water in the cell.
The Role of Osmosis in Plant:
1. Absorption of water from the soil by the root hairs and transporting it to the other parts of plant is performed due to osmosis.
2. Support the plant cells to become in a turgid state, that gives the solidity, especially in the regions that the supporting tissues is not formed like the growth apex regions in root and stem.
3. The higher osmotic concentrations, increases the resistance of plants against high degrees of temperature and drought, because it prevents water loss.
4. The opening and closing process of stomata is combined with the osmotic pressure of the guard cells (as the osmotic pressure increased, the guard cell becomes turgid and the stomata will open at day, but it is vise versa at the night).
• Exp (2): /Clarify Osmosis (by using potato tubers)
• 1. Remove the dermal layer of (2-3) potato tubers and then make 3 cubes in equal size.
• 2. Make a hole in diameter 1cm into the center of each cube in equal height.
• 3. Put 1g of salt NaCl into the first and the second cube and don’t put any substance in the third cube.
• 4. Put the first and the third cubes into (2 Petri dishes) containing distilled water and put the second cube into another Petri dish without distilled water.
• 5. Wait for (2-3 hours) and then you see the changes?
• Exp (1): Observation the Osmotic potential of a plant cell using tissue weight:
1. Obtain and label 6 test tubes from 1 to 6.
2. Place 10ml of (0, 0.2, 0.4, 0.6, 0.8 and 1M) NaCl solution in each tube consequently.
3. Place 10gs of potato cubs in each tube.
4. Allow the potato to stay in the tubes for 40 min.
5. Reweight the potato cubs after the 40 min. passed.
6. Calculate the difference in the weight.
7. Draw a relation between concentration and the difference in weight.
8. Calculate the osmotic potential of the cell, in the concentration which there is nearly no difference in the weight of potato tuber, in the equation below:
Water potential of the cell (ψ) = -22.4 *M*N*T/273
References
• Jacobs, M. H. (1935). Diffusion processes. In Diffusion Processes (pp. 1-145). Springer, Berlin, Heidelberg.
• Brazee, R. D., Bukovac, M. J., & Zhu, H. (2004). Diffusion model for plant cuticular penetration by spray-applied weak organic acid bioregulator in presence or absence of ammonium nitrate. Transactions of the ASAE, 47(3), 629.
• Corzo, B., de la Torre, T., Sans, C., Escorihuela, R., Navea, S., & Malfeito, J. J. (2018). Long-term evaluation of a forward osmosis-nanofiltration demonstration plant for wastewater reuse in agriculture. Chemical Engineering Journal, 338, 383-391.
• Bereschenko, L. A., Heilig, G. H. J., Nederlof, M. M., Van Loosdrecht, M. C. M., Stams, A. J. M., & Euverink, G. J. W. (2008). Molecular characterization of the bacterial communities in the different compartments of a full-scale reverse-osmosis water purification plant. Applied and Environmental Microbiology, 74(17), 5297-5304.
