lecture 2.pptx

botony

1. Pharmaceutical Botany Dr. Badr Eldin Ahmed Eltayeb Associate Professor of Plant Biotechnology

2. Objectives After studying this material you should be able to : Plasmolysis Definition. Plasmolysis and Osmosis. Types of Plasmolysis. Osmosis and How it works . Tonicity. Hypotonic, hypertonic, and isotonic Difference Between Osmosis and Diffusion

3. Plasmolysis Plasmolysis Definition Plasmolysis is when plant cells lose water after being placed in a solution that has a higher concentration of solutes than the cell does.

4. this known as a hypertonic solution . Water flows out of the cells and into the surrounding fluid due to osmosis . This causes the protoplasm , all the material on the inside of the cell, to shrink away from the cell wall . Severe water loss that leads to the collapse of the cell wall can result in cell death. Since osmosis is a process that requires no energy on the part of the cell and cannot be controlled, cells cannot stop plasmolysis from taking place.

5. Plasmolysis and Osmosis Osmosis is responsible for the occurrence of plasmolysis. Osmosis is a special type of diffusion that occurs when water flows into or out of a membrane such as a cell’s plasma membrane . It occurs based on the type of solution that a cell is in. A solution is a mixture that contains a fluid, or solvent (usually water), and a solute that is dissolved in the solvent

6. . When a cell is placed into a hypertonic solution, there is a higher concentration of solutes outside the cell, so water flows out of the cell to balance the concentration on both sides of the membrane. Since plasmolysis is the loss of water from a cell, it occurs when a cell is in a hypertonic solution. Conversely, when a cell is placed into a hypotonic solution , there is a lower solute concentration outside the cell than inside, and water rushes into the cell. In an isotonic solution , solute concentrations are the same on both sides, so there is no net gain or loss of water.

7. Plant cells fare best in hypotonic solutions. This is because when plant cells are full of water, they push against each other to form the basic support structure for the plant and allow it to stand upright. Plant calls full of water are known as turgid cells; they exert turgor pressure on each other. The cells’ rigid cell wall keeps them from bursting. Unlike plant cells, animal cells do not have a cell wall in addition to their cell membrane . When animal cells are placed in a hypotonic solution and too much water rushes in, they will lyse , or burst. They fare best in isotonic solutions instead.

8. This figure shows a plant cell in different types of solutions:

9. Types of Plasmolysis Concave Plasmolysis Concave plasmolysis is a process that can usually be reversed. During concave plasmolysis, the protoplasm and the plasma membrane shrink away from the cell wall in places due to the loss of water; the protoplasm is then called protoplast once it has started to detach from the cell wall. Half-moon-shaped “pockets” form in the cell as the protoplast peels from the surface of the cell wall. This can be reversed if the cell is placed in a hypotonic solution, which will cause water to rush back into the cell.

10. Convex Plasmolysis Convex plasmolysis is more severe than concave plasmolysis. When a cell undergoes complex plasmolysis, the plasma membrane and protoplast lose so much water that they completely detach from the cell wall. The cell wall collapses in a process called ctyorrhysis . Convex plasmolysis cannot be reversed, and results in the destruction of the cell. Essentially, this is what happens when a plant wilts and dies from lack of water .

11. Defenses Against Plasmolysis Plasmolysis happens in extreme cases of water loss, and does not happen very often in nature. Plants have a couple mechanisms to protect against water loss. Stomata, which are small holes on the underside of a plant’s leaves, close to help keep water in the plant. Plants also naturally produce wax that is another defense against water loss.

12. Examples of Plasmolysis Although plasmolysis more commonly happens in a laboratory setting, it can happen in real-life settings as well. For example, during periods of extreme coastal flooding, ocean water deposits salt onto land. Too much salt causes the water to flow out of any plants on the affected land, killing them . .

13. Chemical weedicides are also used to kill unwanted plants through plasmolysis. This same process is also used when a lot of salt and/or sugar is added to preserve food and make jams , jellies, and pickles. The cells lose water and become less conducive to the growth of microorganisms such as bacteria , allowing these food items to be preserved

14. osmosis is the net movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This may sound odd at first, since we usually talk about the diffusion of solutes that are dissolved in water, not about the movement of water itself. However, osmosis is important in many biological processes, and it often takes place at the same time that solutes diffuse or are transported. Here, we’ll look in more detail at how osmosis works, as well as the role it plays in the water balance of cells .

15. How it works Why does water move from areas where solutes are less concentrated to areas where they are more concentrated? This is actually a complicated question. To answer it, let’s take a step back and refresh our memory on why diffusion happens. In diffusion, molecules move from a region of higher concentration to one of lower concentration—not because they’re aware of their surroundings, but simply as a result of probabilities. When a substance is in gas or liquid form, its molecules will be in constant, random motion, bouncing or sliding around one another.

16. If there are lots of molecules of a substance in compartment A and no molecules of that substance in compartment B, it’s very unlikely—impossible, actually—that a molecule will randomly move from B to A. On the other hand, it’s extremely likely that a molecule will move from A to B. You can picture all of those molecules bouncing around in compartment A and some of them making the leap over to compartment B. So, the net movement of molecules will be from A to B, and this will be the case until the concentrations become equal. How it works

17. How it works Why should that be? There are some different explanations out there. TheIn the case of osmosis, you can once again think of molecules—this time, water molecules—in two compartments separated by a membrane. If neither compartment contains any solute, the water molecules will be equally likely to move in either direction between the compartments. But if we add solute to one compartment, it will affect the likelihood of water molecules moving out of that compartment and into the other—specifically, it will reduce this likelihood. one that seems to have the best scientific support involves the solute molecules actually bouncing off the membrane and physically knocking the water molecules backwards and away from it, making them less likely to cross1,2^{1,2}1,2start superscript, 1, comma, 2, end superscript.

18. Tonicity The ability of an extracellular solution to make water move into or out of a cell by osmosis is know as its tonicity . A solution's tonicity is related to its osmolarity , which is the total concentration of all solutes in the solution. A solution with low osmolarity has fewer solute particles per liter of solution, while a solution with high osmolarity has more solute particles per liter of solution. When solutions of different osmolarities are separated by a membrane permeable to water, but not to solute, water will move from the side with lower osmolarity to the side with higher osmolarity . Three terms—hypotonic, isotonic, and hypertonic—are used to compare the osmolarity of a cell to the osmolarity of the extracellular fluid around it.

19. Note : When we use these terms, we are considering only solutes that cannot cross the membrane. If the extracellular fluid has lower osmolarity than the fluid inside the cell, it’s said to be hypotonic — hypo means less than—to the cell, and the net flow of water will be into the cell. In the reverse case, if the extracellular fluid has a higher osmolarity than the cell’s cytoplasm, it’s said to be hypertonic — hyper means greater than—to the cell, and water will move out of the cell to the region of higher solute concentration. In an isotonic solution— iso means the same—the extracellular fluid has the same osmolarity as the cell, and there will be no net movement of water into or out of the cell.

20. Hypotonic, hypertonic, and isotonic are relative terms. That is, they describe how one solution compares to another in terms of osmolarity . For instance, if the fluid inside a cell has a higher osmolarity , concentration of solute, than the surrounding fluid, the cell interior is hypertonic to the surrounding fluid, and the surrounding fluid is hypotonic to the cell interior.

21. Difference Between Osmosis and Diffusion Osmosis is the movement of the solvent (water) from a region of higher concentrations to the region of lower concentration through a semipermeable membrane, to maintain the equilibrium. On the other hand, diffusion can be described as the movement of the molecules (solid, liquid or gases) from the region of higher concentration to the region of lower concentrations, but not through a semipermeable membrane .

22. Definition of Osmosis The function of osmosis is to maintain the equilibrium on both the side of the membrane and so in this process there is the only movement of the water molecule, also called as the solvent .

23. In order to keep the homeostasis the water molecule move sidelong from higher water concentration to the region of lower water concentration . And also from the lower solute concentration to the higher solute concentration. Notably, the water molecules are passed through a semi-permeable membrane . So we can say that osmosis is a special kind of diffusion. Osmosis is important in the distribution of nutrients and in a release of the metabolic waste from the body, and in maintaining the concentration gradient inside and outside the cell. In plants osmosis is helpful in absorbing water from the soil, it helps in maintaining water level, even at the time of loss of water, cell to cell diffusion, also provide mechanical support.

24. Factors affecting osmosis are: Diffusion distance Concentration gradient. Temperature.

25. Osmotic pressure It can be defined as the pressure exerted on the solution, to prevent the passage of the solvent into the solution, where both are separated by a semipermeable membrane .

26. Hypotonic Solution – Solution with relatively low pressure and high solvent concentration, here cells absorbs water, swell, and burst . Hypertonic Solution – Solution with relatively higher osmotic pressure and high solute concentrations, here cells shrivel due to loss of water. Isotonic Solution – Solution with equal osmotic pressure ( iso -osmotic) and the concentration of solute and solvent are at level, so the cell tone is maintained and thus no changes in cell volume and shape.

27. Definition of Diffusion The movements of molecules like solid, gases or liquid, from the region of higher concentration to the region of lower concentration. The reason for this movement is the randomly moving molecules present in high concentration possess free energy, and when they move to the region of lower concentration, equilibrium of diffusing molecule along with the benefit of free energy is achieved. There is no role semi-permeable membrane . Thus diffusion is important in creating energy, at the time of respiration it helps in exchange of gases in animals, it is also helpful in the process of transpiration a nd photosynthesis in plants.

28. Example: If a drop of blue ink is put in the jar filled with water, the ink will get evenly distributed all over the water, and the particles will get distributed everywhere, this is the simplest example of diffusion. Definition of Diffusion

29. Factors affecting diffusion are:   Molecular weight – Larger the molecular weight, slower will be the movement of the molecules.  Concentration gradient – Higher the difference, higher the rate of the motion of molecules  Pressure – Higher the pressure, lower will be the rate of diffusion due to the increase in the number of a collision.  Temperature – Higher the temperature, higher will be the motion of the particles.

30. 1Surface diffusion. 2. Collective diffusion. 3. Electron diffusion. 4. Facilitated diffusion. 5. Brownian diffusion. 6. Effusion . 7. Gaseous diffusion. 8. Photon diffusion. 9. Self-diffusion. 10. Reverse diffusion. 11. Momentum diffusion. 12. Knudsen diffusion. Types of diffusion are: