Mass Transport In Plants

Question 1

Potometer assumption

Answer 1

Water uptake directly related to water loss

Question 2

Potomter method

Answer 2

Cut shoot underwater and at a slant
Underwater, assemble the potometer and insert the root
Remove apparatus from water, keeping end of capillary tube in water
Dry leaves
Allow time for shoot to acclimatise then close the tap
Remove end of capillary tube from beaker till bubble forms then replace in water
Start stopwatch and record distance moved by the bubble per unit time

Question 3

Dissecting plants

Answer 3

Scalpel to cut thin cross section of stem
Tweezers to. Place in water to prevent drying out
Add to dish of stain (TBO) for 1 minute which stains lignin pf xylem blue green
Rinse off sections in water and mount onto slide

Question 4

Is translocation an energy requiring process or not

Answer 4

It’s energy requiring

Question 5

Mass flow hypothesis

Answer 5

Active transport of solutes from companion cell into sieve tube elements
Decreases water potential at source
Water moves by osmosis into sieve tube element from xylem
Increases (hydrostatic) pressure/ produces pressure gradient
Mass flow to respiring cells or to storage tissue/ organ
Enzymes break down solutes at sink so higher water potential there
(Water moves out to xylem by osmosis
Lower pressure
Pressure gradient)
Unloaded/ removed from phloem by active transport?

Question 6

Bark ringing

Answer 6

Remove ring of bark from woody stem (not xylem though)
Bulge forms above ring
Fluid fro bulge has higher concentration of sugars than from below the ring
Evidence of downward flow of sugars

Question 7

Tracers

Answer 7

Plant supplied with organic substance with a radioactive label attached (eg CO2 with 14C)
Radioactive carbon then incorporated into organic substances produced by leaf which will be moved round the plant by translocation
Plant killed by freezing in liquid nitrogen and placed on photographic film- radioactive substance is present in dark areas (autoradiography)

Question 8

Xylem

Answer 8

Transports water and mineral ions in solution
Up the plant to leaves
Xylem vessels- Long tube like structures formed from dead cells joined end to end with no end walls

Question 9

Cohesion tension theory

Answer 9

Transpiration (water evaporates from mesophyll cells due to heat from sun, into air spaces beneath stomata)
Creates tension which pulls more water up to the leaf
Water molecules are cohesive (form hydrogen bonds with each other) so column of water moves up xylem
Water enters stem through roots
Transpiration pull puts xylem under pressure (negative pressure in xylem)

Question 10

Factors affecting transpiration rate

Answer 10

Light
Temperature
Humidity
Wind

Question 11

Other than a change in temperature, give one change the scientist could make to the environmental conditions to increase the cut flowers’ shelf life

Answer 11

Reduce light intensity—-> stomata close——> decreased rate of evaporation/ transpiration
Increase humidity—->reduces water potential gradient between plant and air—->decreased rate of evaporation/ transpiration

Question 12

Evidence supporting cohesion tension theory

Answer 12

Change in diameter of tree trunks according to the rate of transpiration
Day: most transpiration so greatest tension in xylem which pulls walls of xylem inwards