12.3 mass transports in plants

Question 1

what does the phloem tissue transport?

Answer 1

sucrose and organic substances from leaves where they are formed to where they are needed (for example shoots, flowers and fruits in roots)

Question 2

solutes are?

Answer 2

dissolved substances

Question 3

phloem tissue is formed from…

Answer 3

cells arranged in long tubes

Question 4

what are important cell types in phloem tissue?

Answer 4

sieve tube elements and companion cells

Question 5

sieve tubes elements are…

Answer 5

living cells that form the tube for transporting solutes.
They have no nucleus and few organelles

Question 6

each sieve tube element has its own…

Answer 6

companion cells that carry out functions for sieve cells

Question 7

companion cells contain…

Answer 7

many mitochondria to synthesise ATP through aerobic respiration for active transport of solutes

Question 8

sieve tubes are…through…

Answer 8

connected to each other
sieve plates

Question 9

solutes are sometimes called…

Answer 9

assimilates

Question 10

transloction is an… process

Answer 10

energy requiring process

Question 11

it moves from…

Answer 11

sources to sinks

Question 12

how do enzymes maintain a concentration gradient?

Answer 12

from source to sink by concerting the solutes to other storage substances

Question 13

there is a lower concentration gradient…

Answer 13

at sink than source

Question 14

explain source in mass flow hypothesis

Answer 14

• companion cells actively transport sucrose into the sieve tubes of the phloem at the source
• this lowers water potential in sieve tubes
• water enters the phloem sieve tubes by osmosis from xylem
• this creates a high hydrostatic pressure inside sieve tubes at source end of phloem

Question 15

explain sink in mass transport hypothesis

Answer 15

• sucrose actively transported from phloem sieve tubes into sink cells and converted to starch or repaired
  -increases water potential inside sieve tubes so water exits by osmosis
  -this lowers hydrostatic pressure inside the sieve tubes

Question 16

explain mass flow in mass transport hypothesis

Answer 16

• forms a pressure gradient from source end to sink end
• gradient pushes solutes towards the sink (roots and growing regions)
• when they reach the sink the solutes will be used or stored
• higher concentration of sucrose at source the higher rate of translocation

Question 17

Describe the mass flow hypothesis for mechanism of translocation in plants

Answer 17

1. in source/ leaf sucrose actively transported into phloem
2. by companion cells
3. lowers water potential of sieve cell/ tube and water enters by osmosis
4. Increase in pressure causes mass movement towards sink/root
5. Sucrose used / converted in root for respiration for storage

Question 18

ringing experiment observation, evidence for and against

Answer 18

observation
- if a ring of bask which includes the phloem but not the xylem is removed from a woody stem a bulge forms above the ring

Evidence for
- fluid from bulge has a higher concentration of sugars then fluid from below the ring
- this is because sugars can’t move past area where bark has been removed which is evidence of a downward flow of sugars
-conc of sucrose is higher in leaves (source) than root (sink)
-downward flow in pholem during daylight ceases in shade or night

Question 19

ringing experiment observation, evidence for and against

Answer 19

observation
- if a ring of bask which includes the phloem but not the xylem is removed from a woody stem a bulge forms above the ring

Evidence for
- fluid from bulge has a higher concentration of sugars then fluid from below the ring
- this is because sugars can’t move past area where bark has been removed which is evidence of a downward flow of sugars
-conc of sucrose is higher in leaves (source) than root (sink)
-downward flow in pholem during daylight ceases in shade or night