Transport in Plants - Phloem

Question 1

whats the function of the leaves

Answer 1

photosynthesis
carbon dioxide + water > glucose + oxygen

Question 2

what does organic substances refer to in phloem

Answer 2

glucose and dissolved sugars

Question 3

what is the function of the phloem

Answer 3

to transport the organic substances (sugar) produced in the leaves around the rest of the plant to reach cells that need sugar to respire

Question 4

what are the two key cells that make up phloem tissue

Answer 4

sieve tube elements
companion cells

Question 5

where are the sieve tube elements in phloem

Answer 5

down the centre, all lined up

Question 6

where are the companion cells in phloem tissue

Answer 6

alongside the sieve tube elements

Question 7

describe sieve tube elements

Answer 7

living cells that contain no nucleus and very few organelles

Question 8

what do companion cells do

Answer 8

provide ATP which is required for the active transport of organic substances

Question 9

what is the source in the mass flow hypothesis

Answer 9

where the organic substances is produced

Question 10

what is the sink in the mass flow hypothesis

Answer 10

where the organic substance is being transported to

Question 11

briefly explain the movements of solutes from source to sink

Answer 11

source cell (leaf) has higher hydrostatic pressure than the sink cell (respiring cell) so the solutes are forced towards the sink cell from the source via the phloem

Question 12

how do the solutes move from the source cell to the sieve tube elements

Answer 12

• organic substances formed in source cell
• substances diffuse into companion cells via facilitated diffusion
• ## active transport is used to actively load the solutes to transport them from the companion cell into the sieve tube at the source

Question 13

describe movement of sucrose within the phloem sieve tube elements

Answer 13

• increase of sucrose in STElowers the water potential
• water diffuses in via osmosis from surrounding xylem vessels
• increase in water, increases the hydrostatic pressure which forces the liquid down towards the sink

Question 14

how is sucrose transported into the sink

Answer 14

• sucrose is used in respiration at the sink or stored as insoluble starch
• the sucrose is actively transported into the sink which increases the water potential inside the STE > so water leaves the tubes by osmosis into the sink cell / xylem
• this lowers pressure inside the sieve tube element at the sink end
• the concentration gradient is maintained