Plant transport

Question 1

Benefits of an internal transport system

Answer 1

Small SA:V - diffusion from outer surface not sufficent. Transport ensure molecules reach all tissues /
allows high metabolic rate

Question 2

What type of tissue makes up the cambium

Answer 2

Meristem

Question 3

Precautions when setting up a potometer

Answer 3

1) Remove excess water from the surface of leaves before readings are taken
2) The shoot must be kept whilst underwater
3) There should be no extra air bubbles

Question 4

Suggest how water is being lost from the cut stem when all the leaves have been treated with petroleum jelly.

Answer 4

Evaporation from upper leaf surfaces

Question 5

Why does large leaves in a hydrophyte not affect the plant

Answer 5

High rate of transpiration does not matter as
plant lives in an aquatic habitat so water is lost easily
and easily replaced

Question 6

How is glucose translocated to parts of the plant in which it is needed

Answer 6

1) Glucose is converted to sucrose in photosynthesising cells
2) Apoplast pathway
3) Active process
4) Proton pump in companion cells
5) H+ concentration gradient
6) Co-transport of H+ and sucrose into
companion cell
6) Structural adaptations of
companion cells, e.g. many
mitochondria, increase surface
area of cell surface membranes
7) Passive loading via symplast route
8) Role of plasmodesmata
9) entry of sucrose / solutes
decreases water potential of
phloem / sieve elements
10) water enters phloem from
surrounding cells / xylem
11) results in higher hydrostatic
pressure

Question 7

How are the phloem and xylem similar transport systems

Answer 7

Solutes carried in both; both carry minerals/salts; both use mass flow and hydrostatic pressure

Question 8

How are the phloem and xylem different transport systems

Answer 8

1) transport in phloem can take place in
different directions and transport in xylem
only takes place up the plant

2) phloem carries carbohydrates and xylem
does not

3) phloem transport uses living cells and xylem
does not

4) xylem uses, capillary action / cohesion and
adhesion, and phloem does not (1)

Question 9

deduce a possible mechanism to account for the increased unloading and transport of sucrose in the modified plants.

Answer 9

1) sucrose unloaded at sinks and invertase
converts sucrose into, glucose /
monosaccharide

2) increases sucrose concentration gradient
between phloem and sink

3) causes increased unloading of sucrose from
phloem

two from
increases solute gradient between source
and sink
removal of water from phloem increases
pressure gradient between source and sink
(1)
contributes to increased movement in
phloem (1)