Final exam

Question 1

sucrose-proton symporters

Answer 1

move sucrose from the apoplastic space to the phloem (apoplastic pathway)

Question 2

where is acid invertase?

Answer 2

cell wall and vacuole

Question 3

what are the requirements for symplastic phloem loading in the source tissues ?

Answer 3

extensive plasmodesmata connections and continuity

Question 4

what are the 3 potential fates of sucrose generated in a source cell?

Answer 4

• used for respiration
• transported to sink cell
• storage

Question 5

sieve tube elements

Answer 5

• alive at maturity
• no nucleus, few plastids
• many plasmodesmata
• low resistance pathway
• stacked on top of eachother and connected with sieve plates

Question 6

companion cells

Answer 6

attached to sieve tube elements, support metabolic functions

Question 7

What happens when there is a puncture in the phloem?

Answer 7

when flow changes, p-proteins are deposited on the sieve pores to isolate the leak

Question 8

symplastic pathway of phloem loading/unloading

Answer 8

material moves from one cell to the next through the plasmodesmata

Question 9

apoplastic pathway of phloem loading/unloading

Answer 9

sucrose exits source cells, enters apoplastic space, moves towards phloem cells, and is loaded into phloem cells
- requires sucrose-proton symporters to move across membranes

Question 10

Munchs pressure flow model

Answer 10

When solutes are loaded by the source, the increase in solutes draws in more water and increases the pressure. When solutes are unloaded by the sink, the decrease in solutes increases the water potential so water is drawn away from the sink, decreasing the pressure.

Question 11

fates of sucrose unloaded around a sink cell?

Answer 11

• broken down into glucose and fructose outside of the cell
• used by the sink cell for metabolic processes like respiration
• broken down into glucose and fructose inside the cell
• can be stored in vacuoles

Question 12

2 enzymes involved in sucrose metabolism

Answer 12

• invertase: turns sucrose into glucose and fructose
• sucrose synthase: turns sucrose into fructose and udp-glucose

Question 13

main ways a sink cell uses the carbon from sucrose?

Answer 13

• respiration (ATP and carbon backbones)
• synthesizing cell wall components
• storage for later use (sometimes converted into starch by plastids)