osmosis 4.3

What is osmosis?

The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selective permeable membrane.

What is water potential?

it is the pressure created by water molecules
measured in units of pressure

Units are psi

what is the water potential of pure water?

0. Only when 25 degrees and 100kpa

when you add solute to pure water what happens to wp?

it lowers the wp
because more concentrated a solution is

what does the water potential of a solution be?

less than 0 a negative value

where does water move from and to?

Water will move from a region of higher (less water potential) to one of lower to one of (more water potential)

what happens if a value is negative on wp?

the more negative value,the lower the water potential

What happens when both sides of the membrane have the same water potential ?

Osmosis stops because we have reached an equilibrium

Why does the cytoplasm have a low /negative water potential

The cytoplasm of animal cells contains many solutes dissolved in water

What happens when an animal cell is in an isotonic solution ?

Osmosis doesn’t take place because the water potential outside the cell is same as the water potential of the cytoplasm .

Water molecules are still moving but no net movement of water

What happens when an animal cell is placed in a hypotonic solution ?

When placed in pure water (higher water P)
The water potential outside of the cell is greater than the water potential in the cytoplasm.

So water molecules will move inside the cell by osmosis and the pressure is called hydrostatic pressure

However the cell membrane will not be strong enough to resist the large increase in pressure inside the cell causing it to burst

What happens when an animal cell is placed in a hypertonic solution ?

When placed in a solution with a lower water potential the water potential outside of thr cell will be smaller than the water potential in the cytoplasm

So water will move out if the cell by osmosis and the cell will shrink

What is different about the environment around animal and plant cells?

in animal cells-the water potential of the surrounding liquid is tightly controlled, so water potential in the cytoplasm and outside it is the same.
-Unlike plants cant easily control the environment around their cells.

what is a protoplast

it is located between the vacuole and the cell wall
-it consists of the cell membrane,the cytoplasm and the organelles found in the cytoplasm.

what is the water potential of the interior of plant cells?

low water potential because of the dissolved solutes

What is incipient plasmolysis, and when does it take place?

-it occurs when the protoplast begins to pull away from the cell wall
-it takes place when the plant cell is placed in a solution with the same water potential (isontonic solution)

what happens when a plant cell is in a hypotonic solution?

-when placed in pure water, the water potential outside is greater than inside= which causes water to enter the cell by osmosis.
this causes the hydrostatic pressure to increase

-as a result, the protoplast pushes outwards against the cell wall-but since it is strong ,the plant cell won't burst and becomes firm.

-the plant cell is now turgid +and internal pressure is called turgor pressure

at certain point,it prevents nay more water from entering.

What happens when a plant cell is in a hypertonic solution?

-if a plant cell is placed in a solution with lower water potential than inside the cytoplasm -this causes water to move out of the cell by osmosis

-the protoplast would pull away from the cell wall,so the plant cell become plasmolysed.

-this results in the space between the cell membrane and the cell wall to be filled with the solution surrounding the plant cell.

protoplast :shrinks