Biology movement of substances

Concentration gradient

Concentration gradient is the difference in concentration between two regions.

Diffusion

Diffusion is the net movement of particles from a region where they are of higher concentration to a region where they are of lower concentration, down a concentration gradient without the need for energy.

Factors that affect the rate of diffusion

1. diffusion distance

2. concentration gradient

3. s.a. to v. ratio

4. temperature

osmosis

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

Water potential

Tendency of water molecules to move from one place to another.

Dilute = higher water potential

concentrated = lower water potential

higher concentration of solutes = lower water potential

Ans:

1. contrast region of concentration

2. net movement of x molecules

3. by (process)

4. direction of movement e.g. into the cell sap

5. end result

Plant cells in a solution with higher water potential

1. Cell sap has a lower water potential than that of the solution outside the cell

2. By osmosis, water molecules enter the cell through the partially permeable cell membrane.

3. As water molecules enter the cell, the vacuole increases in size and pushes the cytoplasm against the cell wall

4. The cell swells and becomes turgid.

4. cell does not burst as it is protected by the inelastic cell wall

turgor pressure

The pressure exerted by the water in the vacuole is the turgor pressure.

-prevents the plant from wilting

-causes the opening and closing of the stomata in a guard cell

Animal cells in a solution with higher water potential

1. Cytoplasm has a lower water potential than that of the solution outside the cell

2. By osmosis, water molecules enter the cell through the partially permeable cell membrane into the cytoplasm.

3. As water molecules enter the cell, the cytoplasm increases in size and pushes against the cell membrane

4. As there is no cell wall to protect the cell, the animal cell swells and bursts

5. The animal cells is haemolysed

Plant cells in a solution with lower water potential

1. Cell sap has a higher water potential than that of the solution outside the cell

2. By osmosis, water molecules from the vacuole and cytoplasm leave the cell through the partially permeable cell membrane to the surrounding solution.

3. As water molecules leave the cell, the vacuole decreases in size

4. The cytoplasm and cell membrane shrinks away from the cell wall.

5. the cell is plasmolysed

6. The cell decreases in size and becomes flaccid.

Animal cells in a solution with lower water potential

1. Cytoplasm has a higher water potential than that of the solution outside the cell

2. By osmosis, water molecules from the cytoplasm leave the cell through the partially permeable cell membrane to the surrounding solution.

3. As water molecules leave the cell, the cytoplasm decreases in size

4. The cell undergoes crenation, shrinks and becomes spiky

Active transport

Active transport is the process of in which energy is used to move the particles of a substance across a membrane against its concentration gradient, from a region of lower concentration to a region of higher concentration.

(must have pp membrane)