Transport across membranes PPQs

Question 1

Give two ways in which pathogens can cause disease. (2 marks)

Answer 1

1. (Releases) toxins;

2. Kills cells / tissues.

Question 2

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar. Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria. (3 marks)

Answer 2

1. water potential in honey lower (than in bacterial cells);
2. Water leaves bacteria / cells by osmosis;
3. (Loss of water) stops (metabolic) reactions.

Question 3

Low-density lipoprotein (LDL) is a substance found in blood.
LDL enters the liver cells (lines 3−4). Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell. (2 marks)

Answer 3

1. Lipid soluble / hydrophobic

2. Enters through (phospholipid) bilayer

Question 4

Explain how the monoclonal antibody would prevent the regulator protein from working (2 marks)

Answer 4

1. (Monoclonal antibody) has a specific tertiary structure /is complementary to regulator protein
2. Binds to / forms complex with (regulator protein)
3. (So regulator protein) would not fit / bind to the receptor / is not complementary to receptor

Question 5

The stomata close when the light is turned off. Explain the advantage of this to the plant. (2 marks)

Answer 5

1. (Because) water is lost through stomata;
2. (Closure) prevents / reduces water loss;
3. Maintain water content of cells.

Question 6

In both Treatment 1 and Treatment 2, the uptake of carbon dioxide falls to zero when the light is turned off. Explain why. (2 marks)

Answer 6

1. No use of carbon dioxide in photosynthesis (in the dark);
2. No diffusion gradient (maintained) for carbon dioxide into leaf / there is now a diffusion gradient for carbon dioxide out of leaf (due to respiration).

Question 7

Arteriole end direction of blood flow Venule end Hydrostatic pressure = 4.3 kPa Hydrostatic pressure = 1.6 kPa Tissue fluid Hydrostatic pressure = 1.1 kPa (a)
Use the information in the figure above to explain how tissue fluid is formed (2 marks)

Answer 7

1. (Overall) outward pressure of 3.2 kPa;

2. Forces small molecules out of capillary.

Question 8

High blood pressure leads to an accumulation of tissue fluid. Explain how (3 marks)

Answer 8

1. High blood pressure = high hydrostatic pressure;
2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Question 9

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why. (3 marks)

Answer 9

1. Water has left the capillary;
2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).

Question 10

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values. (2 marks)

Answer 10

1. Divide mass of each lipid by total mass of all lipids (in that type of cell);
2. Multiply answer by 100.

Question 11

Describe how you would use the student’s results in the table above to find the water potential of the potato tissue. (3 marks)

Answer 11

1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
2. Find concentration where curve crosses the x-axis;
3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis)

Question 12

Explain why the data in the table above are described as processed results. (1 mark)

Answer 12

Calculations made (from raw data) / raw data would have recorded initial and final masses.

Question 13

Give 2 ways in which active transport is different to facilitated diffusion (2 marks)

Answer 13

1. AT molecules go against conc. gradient whereas in facilitated go down
2. AT requires energy from hydrolysis of ATP whereas facilitated is passive
3. AT uses only carrier proteins whereas facilitated uses carrier and channel

Question 14

Describe how you would use a 1.0 mol dm−3 solution of sucrose to produce 30 cm3 of a 0.15 mol dm−3 solution of sucrose. (2 marks)

Answer 14

Add 4.5 cm3 of (1.0 mol dm-3) solution to 25.5 cm3 (distilled) water.

Question 15

Explain why the structure of a membrane is described as fluid mosaic. (2 marks)

Answer 15

1. proteins are dispersed/embedded
2. in a variety of sizes and shapes
3. looks like a mosaic