transport across cell membranes.

Question 1

Describe the difference between passive and active transport.

Answer 1

• Passive has no energy input.
• Active requires energy in the form of ATP.

Question 2

Examples of active and passive transport.

Answer 2

Active = Active transport.
Passive = Diffusion, facilitated diffusion, osmosis.

Question 3

Define the term osmosis.

Answer 3

• The net movement of water
• From a high water potential to a low water potential
• Through a selectively partially permeable membrane.

Question 4

What happens to an animal cell when it is places in distilled water?

Answer 4

• The cell bursts.
• The water potential outside the cell is higher than the water potential inside the cell.
• Water moves into the cell by osmosis.

Question 5

What happens to a plant cell when it is placed in distilled water?

Answer 5

• The cell becomes turgid.
• The water potential outside the cell is higher than the water potential inside the cell.
• Water moves into the cell by osmosis.

Question 6

What happens to an animal cell when it is places in a concentrated salt solution?

Answer 6

• The cell shrinks (becomes crenated).
• The water potential inside the cell is higher than the water potential outside the cell.
• Water leaves the cell by osmosis.

Question 7

What happens to a plant cell when it is placed in a concentrated salt solution?

Answer 7

• The cell becomes plasmolysed.
• The cell membrane moves away from the cell wall.
• The water potential inside the cell is higher than the water potential outside the cell.
• Water leaves the cell by osmosis.

Question 8

Describe how you would find out the water potential inside carrot cells.

Answer 8

• Cut the carrot into 6 1cm cubes.
• Find the mass of each cube.
• Place each carrot cube into a separate test tube.
• Add 5cm cubed of a different salt solution to each test tube (0.0, 0.2, 0.4, 0.6, 0.8, 1.0M).
• Leave for 20 minutes.
• Remove each carrot cube and blot it.
• Find the mass again.
• Calculate the percentage change for each carrot cube.
• Repeat 2 more times.
• Spot anomalous results and calculate a mean.
• Plot a graph of salt concentration against percentage change.
• Draw a line of best fit.
• The concentration of the carrot cells is where the line crosses the x axis.

Question 9

Factors that increase the rate of diffusion.

Answer 9

• Increased concentration gradient.
• Increased temperature.
• Increased surface area.
• Thinner exchange surface area.

Question 10

Describe how active transport is carried out.

Answer 10

• The molecule attaches to a carrier protein.
• The carrier protein changes shape.
• This moves the molecule to the other side of the membrane.
• Requires ATP.

Question 11

Describe how exocytosis is carried out.

Answer 11

• The molecule is packaged in a vesicle.
• The vesicle ie moved to the plasma membrane by the cytoskeleton.
• The vesicle fuses with the plasma membrane.
• The molecule is released.
• Requires ATP.

Question 12

Describe how endocytosis is carried out.

Answer 12

• The plasma membrane surrounds the substance / molecule.
• Forms a vesicle.
• The cytoskeleton moves the vesicle into the cell.