Mass transport in plants

Question 1

Give two ways in which the structure of starch is similar to cellulose.

Answer 1

• 1 - Both polymers

- 2 - Both contain glycosidic bonds

Question 2

Give two ways in which the structure of starch is different from cellulose.

Answer 2

• 1 - Starch contains alpha glucose

- 2 - No hydrogen bonds between molecules

Question 3

Using the diagram, suggest and explain one other way in which sieve cells are adapted for mass transport.

Answer 3

• Few organelles

- So more flow of sugars

Question 4

Using the diagram, suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells.

Answer 4

• Mitochondria release energy

- For active transport

Question 5

One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a lower pressure in the roots.

Describe how a high pressure is produced in the leaves.

Answer 5

• Water potential lowers as sugars enter the phloem
• Water enters the phloem by osmosis
• Increased volume of water increases the pressure

Question 6

During this experiment, the scientists ensured that the rate of photosynthesis of their plants remained constant.
Explain why this was important.

Answer 6

• Rate of photosynthesis is related to rate of sucrose production
• Rate of translation is higher when sucrose concentration is higher

Question 7

The scientist concluded that some translocation must occur in the spaces in the cell walls.
Explain how the information in the figure above supports this conclusion.

Answer 7

• Rate of translocation still occurs after 120 minutes

- however sucrose is no longer able to enter the cytoplasm of phloem cells

Question 8

Contrast the processes of facilitated diffusion and active transport

Answer 8

• Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins
• Facilitated diffusion doesn’t require ATP however active transport uses ATP
• Facilitated diffusion occurs down a concentration gradient whereas active transport occurs against a concentration gradient

Question 9

Calculate the ratio of the mean rate of uptake of chloride ions in the first hour to the rate of uptake of chloride ions in the second hour for group B plants.

Answer 9

• 3.3:1

Question 10

Explain the results shown in the figure above.

Answer 10

• For group A, initial uptake is slower because diffusion is occurring only it also levels off due to the same concentration of ions inside and outside the cell
• For group B, uptake is faster as diffusion and active transport are taking place, it also doesn’t level off because no equilibrium is reached

Question 11

Describe the mass flow hypothesis for the mechanism of translocation in plants.

Answer 11

• In the source, sugars are actively transported into the phloem
• By companion cells
• Lowers water potential of sieve cells and water enters by osmosis
• Increase in pressure causes mass movement

Question 12

Name the process that produces the ^14CO2 released from the trunk.

Answer 12

• Respiration

Question 13

How long did it take the ^14C label to get from the top of the trunk to the bottom of the trunk?
Explain how you reached your answer.

Answer 13

• 30 hours

- time between peak ^14C at the top of the trunk and the bottom of the trunk

Question 14

What other information is required in order to calculate the mean rate of movement of the ^14C down the trunk?

Answer 14

• length of the trunk