Topic 2B - Year 1 - Cell Membranes - Osmosis

Question 1

What is Osmosis?

Answer 1

Osmosis is the movement of water molecules across a partially permeable membrane form a high water potential to a Low water potential

Question 2

What is meant by a high water potential?

Answer 2

If something has a high water potential then it has a high concentration of water molecules.

Question 3

What is meant by something having a low water potential?

Answer 3

If something has a low water potential then it has a low concentration of water molecules.

Question 4

What is the water potential of pure water?

Answer 4

Pure water has a water potential of 0

Question 5

If the water potential of something is highly negative what can be said about that solution?

Answer 5

The solution is very concentrated.

Question 6

If two solutions have the same water potential what can be said about the solutions?

Answer 6

The solutions are isotonic

Question 7

If a cell is put in an isotonic solution what will occur?

Answer 7

If a cell is placed in an isotonic solution no osmosis will occur as there will be no concentration gradient.

Question 8

If a solution has a higher water potential than the cell which is placed with in it , the solution can be referred to as?

Answer 8

Hypotonic

Question 9

If a solution has a lower water potential than the cell which is placed within it it can be referred to as?

Answer 9

Hypertonic

Question 10

If a cell is placed in a hypotonic collation what happens?

Answer 10

If a cell is placed in hypotonic solution then the solution has a higher water potential than the cell itself hence water moves into the cell down the water potential gradient to bring the concentrations to an equilibrium.

Question 11

If a cell is placed in a hypertonic solution what happens?

Answer 11

If a cell is placed in a hypertonic solution then the water potential of the solution is lower than that of the water potential in the cell , water thus moves out from the cell into the solution to even the water potential gradient until an equilibrium is reached.

Question 12

Which 3 factors affect the rate of osmosis?

Answer 12

The water potential gradient
The thickness of the exchange surface
The surface area of the exchange surface

Question 13

How does the water potential gradient affect the rate of osmosis?

Answer 13

Higher water potential gradient will increase the rate of osmosis.

Question 14

How does the thickness of the exchange surface affect the rate of osmosis?

Answer 14

The thinner the exchange surface the faster the rate of osmosis .

Question 15

How does the surface area of the exchange surface affect the rate of osmosis?

Answer 15

The greater the surface area the greater the rate of Osmosis.

Question 16

Osmosis can cause a plant cell to become flaccid , under what circumstances would this happen?

Answer 16

A plant cell becomes flaccid when it looses water , water is lost from a plant cell when it is put in a hypertonic solution (absolution which has a lower water potential than the cell itself).

Question 17

Osmosis can cause a plant cell to become plasmolysed, under which circumstances would this occur?

Answer 17

A plant cell becomes plasmolysed when so much water is lost from the cell that the cytoplasm pulls away from the cel wall, an occasion in which lots of water would be lost from the cell would be iff the cell was put in a hypertonic solution where the water potential outside the cell had an extremely low water potential in comparison to the water potential in the cell.

Question 18

Osmosis can cause a plant cell to become turgid , what is meant by turgid and under what circumstance would a plant cell become turgid?

Answer 18

A plant cell becomes turgid when water enters the cell by osmosis in consequence of being put in a hypotonic solution (a solution which has a higher water potential than the cell itself) , the plant cell swells up becoming hard but does not burst as the cell wall holds it together.

Question 19

Under what circumstance would a red blood cell be heaymolised?

Answer 19

A red blood cell would become heamolised if the water potential outside was greater than the water potential inside of the cell , this would cause water to move down the water potential gradient into the cell and as it is not bound by a cell wall it would simply burst.

Question 20

Under which circumstance would an membrane bound cell become crenated?

Answer 20

A membrane bound cell would become crenated when the water potential outside of the cell is much lower than the water potential inside the cell .