phloem and translocation - lqc 2d

Question 1

transfer cell function

Answer 1

for loading sucrose into the sieve tube at source, or unloading at sink

Question 2

sieve tube function

Answer 2

has sieve plates which have sieve pores so fluid can flow through

Question 3

companion cell function

Answer 3

has organelles which provide metabolic support for the sieve tube element cells

Question 4

peripheral cytoplasm of sieve tube function

Answer 4

has very few organelles so less resistance to fluid flow

Question 5

step 1 of translocation in the phloem

Answer 5

At the source (eg. leaf) , sucrose is produced (from glucose and fructose)

Question 6

step 2 of translocation in the phloem

Answer 6

Transfer cells actively pump sucrose into phloem sieve tubes against a concentration gradient, using energy in the form of ATP from respiration

Question 7

step 3 of translocation in the phloem

Answer 7

There is a high sucrose concentration in sieve tube at the source

Question 8

step 4 of translocation in the phloem

Answer 8

This draws water into sieve tube by osmosis from adjacent xylem vessels, increasing the hydrostatic pressure at the loading end of the sieve tube

Question 9

step 5 of translocation in the phloem

Answer 9

Fluid in sieve tube flows from high to low hydrostatic pressure by mass transport

Question 10

step 6 of translocation in the phloem

Answer 10

Sucrose is actively unloaded (using ATP) in sinks (where the sugars are needed) therefore solute concentration decreases in the sieve tube at the sink

Question 11

step 7 of translocation in the phloem

Answer 11

Water moves back into the xylem by osmosis , decreasing the hydrostatic pressure