B2.2 - Movement in and out of cells

Question 1

define diffusion

Answer 1

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient as a result of random movement.

Question 2

what are different factors which affect diffusion?

Answer 2

surface area, concentration gradient, temperature and distance

Question 3

how does surface area affect the rate of diffusion?

Answer 3

• The bigger the surface area the faster the rate of diffusion
• A larger surface area gives more space for diffusion to occur, if it was a smaller space there isn’t much need for diffusion, therefore, the rate of diffusion increases.

Question 4

how does concentration gradient affect the rate of diffusion?

Answer 4

• Bigger concentration gradient will increase the rate of diffusion
• Concentration gradient is the amount of molecules in a cell and out of a cell
• The larger the difference in concentration between high and low this will increase the rate of diffusion because the molecules need to diffuse more, so they move faster.

Question 5

how does temperature affect the rate of diffusion?

Answer 5

• Higher temperature will increase the rate of diffusion

- This is because the particles experience more kinetic energy which increases the diffusion rate.

Question 6

how does distance affect the rate of diffusion?

Answer 6

• The shorter the distance will increase the rate of diffusion.
• This is because the particles don’t need to move around as much

Question 7

define osmosis.

Answer 7

Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.

Question 8

what are the different types of water concentration?

Answer 8

pure water, concentrated solution (small salt or other solutions), highly concentrated solution

Question 9

explain the water concentration of ‘pure water’

Answer 9

• In pure water, the cell contents such as cytoplasm and vacuole push against the cell wall making the cell turgid (firm).
• This is because water moves from a higher water potential to a lower water potential which is outside the cell to inside the cell.
• In an image this cell would be the biggest.

Question 10

explain the water concentration of ‘concentrated solution’

Answer 10

• In a more concentrated solution, the lower water potential would be outside of the cell
• So water moves from a higher water potential which is inside the cell to a lower water potential, outside the cell
• From this the cell loses water, so it loses turgor pressure and becomes flaccid as and it is becoming plasmolyzed.
• In an image this cell would be the medium sized one.

Question 11

explain the water concentration of ‘highly concentrated solution’

Answer 11

• The higher water potential would again be inside the cell, therefore water is lost to the lower water potential, outside the cell
• The cell undergoes full plasmolysis and this cell loses the most water.
• The cell loses all turgor pressure and becomes very flaccid.
• In an image this cell would be the smallest

Question 12

explain the importance of water potential and osmosis in the uptake of water in plants.

Answer 12

• Water potential is the ability of water to leave the system
• The molecules in liquids move randomly and they move from a region of higher water potential to a region of lower water potential.
• This means that water is more likely to flow to a concentrated solution where there is less water present from a dilute solution where more water is present.
• This means, in order for water to diffuse through plant cells, the water potential gradient has to be maintained – plant cells must have a lower water potential than its surrounding environment.

Question 13

explain the importance of water potential and osmosis on animal cells and tissues

Answer 13

• Animal cells, like plant cells lose and gain water as a result of osmosis
• Animal cells don’t have a cell wall, the results of an experiment will appear more severe.
• If a plant cell is placed in a strong sugar solution, so the lower water potential is outside the cell, it will lose water by osmosis and becomes crenated (animal cell term for shrivelled up)
• If an animal cell is placed into distilled water, with a higher water potential than the cell, it will gain water by osmosis and as it has no cell wall to create turgor pressure it will continue to do so until the cell membrane is stretched too far and it bursts.