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.
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. • 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.
19. 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.
20. • 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.
21. 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.
22.
23. 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.
24.
25. 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.
26. • 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.
29. 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.
30. 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.
31. 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 and
photosynthesis in plants.
32. • 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
33. 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.
