Mass transport in plants

Question 1

factors affecting transpiration:

Answer 1

light- positive-stomata open- larger surface area for evaporation
temperature- positive- more kinetic energy- faster evaporation
wind- positive- blows away humid air containing- decreases water potential outside of leaves
humidity- negative- higher water potential outside of leaf- reduces water potential gradient

Question 2

How water moves through plants:

1) root to xylem:

Answer 2

dissolved substances in cell sap- make water potential of roots lower than soil- absorbs water by osmosis

symplast pathway: water enters cytoplasm of cells through plasma membrane and then through plasmodesmata between cells

apoplast pathway: water moves in the cell wall

once water reaches a layer of suberin- the casparian strip- can only pass through the symplast pathway

water moves down water potential gradient until it reaches the xylem

Question 3

cohesion tension theory:

Answer 3

water is dipolar- hydrogen bonds formed between molecules of water- cohesion/ stickiness- water travels up the xylem as a continuous column

adhesion- water sticks to xylem walls

Question 4

how does water move up the xylem:

Answer 4

water vapour evaporates out of stomata of the leaves, creates low pressure

more water is pulled up the xylem to replace the water lost

due to hydrogen bonds between molecules- water molecules are cohesive to each other and adhesive to the xylem walls- moves up as a continuous column

as the water is pulled up the xylem it creates tension pulling the xylem in narrower

Question 5

Mass flow hypothesis:

Answer 5

organic molecules like sucrose are produced from photosynthesis
facilitated diffusion to companion cell
active transport of H+ ions into cell walls creates a diffusion gradient for H+ to diffuse into the sieve tube element
H+ and sucrose co transported through co transport protein carriers into sieve tube element
decreases water potential- water enters phloem by osmosis from xylem
increased volume increases hydrostatic pressure causing liquid to move towards the sink
sugars used in respiring cells- sugars actively transported into sink cells- increases water potential, water leaves phloem to xylem by osmosis- decreases hydrostatic pressure

Question 6

Tracers

Answer 6

plants are supplied radioactive CO2 that’s used in making sugars in photosynthesis
slices of the stems are cut and turn x-ray film black when exposed to radioactive material
the sections of the stem containing the sugars turn black, highlights the phloem and shows where the sugars are transported from

Question 7

Ringing experiment

Answer 7

ring of bark and phloem are removed from a tree trunk

trunk swells above the ring

liquid in the swelling contains sugar

shows when the phloem is removed, the sugars cannot be transported

proves phloem transports sugars