translocation

Question 1

what is translocation

Answer 1

movement of dissolved substances to where they are needed in the plant

Question 2

where does translocation occur

Answer 2

phloem

Question 3

what type of process is translocation

Answer 3

active

Question 4

what is a source

Answer 4

where the substance is made so its in high concentration

Question 5

what is a sink

Answer 5

where the substance is used up so in low concentration

Question 6

why is sucrose transported

Answer 6

it is soluble so easily transported and metabolically inactive so doesnt get used up

Question 7

what is the source and sink for sucrose

Answer 7

source is the leaves as this usually makes sucrose and sink is the other areas of the plant such as food storage organs and meristems

Question 8

how can parts of the plant act as a source and a sink

Answer 8

sucrose can be stored in the roots, however in growing season, this sucrose is transported to the leaves with energy for growth where the leaves act as a sink

Question 9

how do enzymes help movements from source and sink

Answer 9

maintain conc gradients by changing the dissolved substances at the sink

Question 10

what do enzymes ensure

Answer 10

ensures there is always a lower concentration of substance at the sink than the source

Question 11

give an example of enzymes affecting source and sink movement in potatoes

Answer 11

sucrose is broken down into glucose and fructose at the sink, so there is a lower concentration of this at the sink than the source

Question 12

what happens first according to the mass flow hypothesis

Answer 12

active transport is used to actively load the solutes (sucrose) into the sieve tubes of the phloem at the source (leaves)

Question 13

what does the addition of sucrose in the leaves cause

Answer 13

water potential inside the sieve tubes lowers so that water can enter the tubes via osmosis

Question 14

why does water move into the sieve tubes in mass flow

Answer 14

to create a high pressure in the source end of the phloem

Question 15

what happens at the sink end in mass flow

Answer 15

solutes are removed from the phloem to be used up

Question 16

when solutes are removed from the sink in mass flow, what does this cause

Answer 16

increases the water potential inside the sieve tubes so that water leaves the tubes via osmosis

Question 17

what does water moving out of the sink end cause

Answer 17

pressure to fall

Question 18

what does the changes in pressure by osmosis at the source and sink create

Answer 18

a pressure gradient from source to sink to push solutes along

Question 19

how do substances enter the source of the phloem

Answer 19

active loading

Question 20

where is the concentration of sucrose at its highest and lowest

Answer 20

lowest - surrounding tissues -> companion cells -> sieve tubes

Question 21

what is the first stage of active loading

Answer 21

in the companion cell, ATP is used to actively transport H+ ions out of the cell into surrounding tissue

Question 22

what does the movement of H+ out of the companion cell cause

Answer 22

formation of concentration gradient as there are more H+ ions out of the companion cell than inside

Question 23

what happens to the H+ ions that have been actively transported out of the companion cells

Answer 23

bind to a co transporter protein at the companion cell membrane and re enter the cell down their concentration gradient

Question 24

how does sucrose enter the companion cells

Answer 24

bind to the same co transporter as H+ ions, the movement of H+ into the cell aids the movement of sucrose into the cell against conc gradient

Question 25

how does sucrose reach the sieve tubes

Answer 25

via the plasmodesmata of the companion cells against their conc gradient again