3.2 The movement of Substances across the Plasma Membrane in Everyday life

Posted on: March 24, 2011

The effects of hypotonic, hypertonic and isotonic solutions on plant and animal cells

In comparing two solutions with different
solute concentrations:

•The solution with higher solute
concentration is said to be hypertonic
•The solution with a lower solute

concentration is hypotonic (‘hypo’: less)

•Solutions in which the concentration of solute are equal are said to be isotonic(‘iso’: equal)

Animal and plant cells in an isotonic solutions

An isotonic solution is a solution in which the concentration of solute is equal to that of the cytoplasm of the cell .
•Water diffuses into and out of the cell
by osmosis at equal rates
•Therefore there is no net movement of
water across the plasma membrane
[no net gain or net loss of water]
•The cells retain their normal shape

Animal and plant cells in a hypotonic solutions

Solutions which contain a higher concentration of water than that of the cytoplasm are called hypotonic solutions
•Hypotonic solutions contain lower concentration of solute than the cell
•Since the concentration of water is higher outside the cell, there is net movement of water from outside of the cell into the cell by osmosis
•The cells gains water, swells and the internal pressure increases.
The effects of hypotonic solutions on plant cells
1. When plant cells are immersed in a hypotonic solution water
diffuses into the large central vacoule by osmosis
2. The solution outside of the cell is less concentrated than the inside of the cell

3. The large central vacoule expands, causing the cell to swell

4. In this condition, the cell is said to be turgid and firm as a result of the net flow of water into the cell

5. The plant cell does not burst because the rigid cell wall is strong enough to resist the increasing pressure within

6. The swelling plant cell in a hypotonic creates turgor pressure within the cell. This pressure prevents the cell from taking I too
much water and bursting as an animal cell would

7. Turgor pressure is very important to plant cells as it supports and maintains the shape of the cells

Animal and plant cells in a hypertonic solutions

In animal cell, there is a net movement of water from inside to outside of the cell.

This causes the cell to shrink.

In red blood cell, the cell shrivel and the plasma
membrane crinkles up.

The cell has undergone crenation.

In plant cell, water diffuse

out of vacuole through osmosis. Both vacuole and cytoplasm shrink and plasma

membrane pulls away from cell wall (plasmolysis). The cell becomes flaccid. The

flaccidity causes the plant to become limp and stem to drop (wilting). The cell can

deplasmolysed by immersing it back to a hypotonic solution.

Wilting of plant

•Wilting occurs in plants when too much fertilizers like potassium nitrate is
given. Too much fertilizers cause the soil to turn hypertonic to the plant cell.

As a result, water diffuses from the cell sap into the soil by osmosis and the
cell is plasmolysed. Water shortage in soil also causes the plant to wilt.

Food preservation

Food preservatives (salt and sugar). The preservative makes the surroundings

more hypertonic to the food and causes water to leave through osmosis. The

es dehydrated. Microbes loses water to the surrounding and dies.

here is the pictures about 🙂 take a view .

An illustration of water movement in hypertonic and hypotonic solution


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