3.4.2 translocation

Question 1

describe the structure of the phloem tissue

Answer 1

• made of sieve tube elements which are long, living cells arranged end to ends
• companion cells which carry out metabolic functions for the sieve tube elements and actively transport sucrose into the sieve tube

Question 2

how are sieve cells adapted

Answer 2

• contain few organelles so more flow of organic substances

Question 3

how are companion cells adapted

Answer 3

• lots of mitochondria which release ATP for active transport of organic substances

Question 4

what is translocation

Answer 4

• the transport of organic molecules from one part of a plant to another part
• mass flow from source of production to the sink which are the sites of use or storage

Question 5

outline the process of how sucrose transports from source to sieve tube element

Answer 5

• photosynthesis occurring in chloroplasts of leaves creates organic substances e.g sucrose
• sucrose is actively transported into the phloem by companion cells

Question 6

outline movement of sucrose within phloem sieve tube element

Answer 6

• high concentration of sucrose in sieve tubes lowers water potential
• water enters sieve tube from xylem via osmosis
• increase in water volume produces higher hydrostatic pressure at source causing mass flow to respiring cells/storage tissue

Question 7

outline transport of sucrose to sink

Answer 7

• sucrose is removed from phloem by active transport into respiring sink cells for use or storage as starch
• causes water potential of cells to decrease
• so water moves into respiring cells by osmosis
• decreases volume increases hydrostatic pressure sieve tube so hydrostatic pressure decreases
• movement of substances is due to difference in hydrostatic pressure between source and sink end of sieve tube

Question 8

how is a control used when investigating the effect of substance X on translocation

Answer 8

• to compare effects of other treatments as it acts as a baseline
• measure effect of substance X