Plant transport

Question 1

what is transpiration

Answer 1

• loss of water vapour by evaporation through the stomata

Question 2

what 4 factors affect rate of transpiration ?

Answer 2

1. temperature = at high temp = particles have more Ke so move out of stomata faster
2. humidity = low humidity = increased transpiration rate = inc water pot gradient
3. air movement / wind = more wind = increased transpiration rate = air blows away water vapour around stomata so increased water vapour potential gradient
4. light intensity = increased light intensity = increased transpiration rate = more stomata are open to allow co2 to enter for photosynthesis

Question 3

what are xerophytes + what are 3 adaptations ?

Answer 3

• adapted to live in dry conditions = to prevent water loss by transpiration

1. thick waxy cuticle = to prevent water loss
2. sunken stomata in pits = stomata are sheltered from the wind which slows down transpiration rate
3. hairy leaves = traps moist air = reduces water vapour potential gradient

Question 4

what are hydrophytes + what are there adaptations ?

Answer 4

= live in water

1. stomata on upper surfaces of leaf = to increase water loss
2. thin/ no waxy cuticle

Question 5

what is the apoplast pathway ?

Answer 5

apoplast pathway = movement of water through cell wall (non-living parts) by diffusion

Question 6

what is translocation ?

Answer 6

• movement of assimilates (sucrose) by mass flow from ‘source to sink’

Question 7

outline the process of translocation

Answer 7

• H+ ions are actively transported out of companion cell using ATP
• increased conc of H+ ions outside of cell
• H+ ions binds to co-transporter protein + so does sucrose + move back into companion cell by facilitated diffusion
• sucrose diffuses into STE through plasmodesmata = decreases water potential in STE
• water moves into STE by osmosis = generates hydrostatic pressure for mass flow.

Question 8

compare the structure of a xylem with a phloem

Answer 8

BOTH = made up of cells joined end to end + both have no nucleus
- xylem has lignin whereas phloem does not
- xylem has no end walls whereas phloem has sieve plates
- xylem has pits whereas phloem does not
- xylem has vessels whereas phloem does not
- phloem has companion cell whereas xylem does not
- xylem = dead cells vs phloem = living

Question 9

what is the symplast pathway ?

Answer 9

water moves continuously through (living parts) cytoplasm + plasmodesmata via osmosis

Question 10

How does water move through the endodermis ?

Answer 10

endodermis contains Casparian strip ( made of suebrin + impermeable to water) so water has to enter through symplast pathway

Question 11

How does cohesion + tension help water move up plants ?

Answer 11

• water evaporates from leaves out the stomata
• reduces water pot
• this creates tension in xylem which pulls more water into the leaf
• water molecules are cohesive (stick together) so water pulled up as a column

Question 12

what is adhesion ?

Answer 12

water molecules attracted to walls of xylem vessels

Question 13

what are 2 adaptions of STE that enable mass flow to occur?

Answer 13

no nucleus + few organelles
little cytoplasm

Question 14

what is the transpiration stream (2) ?

Answer 14

movement of water up xylem vessels from roots to leaves

Question 15

What can u see in companion cell using an electron microscope (2) ?

Answer 15

• many mitochondria + ribosomes
• plasmodesmata

Question 16

how are new xylem cells formed

Answer 16

in meristem by differentiation

Question 17

How can students observe position of xylem vessels on leaf stalk

Answer 17

• cut transversely
• add stain + observe with microscope under low power

Question 18

what is function of pits in xylem

Answer 18

lateral movement of water

Question 19

what do we assume when measuring rate of transpiration ?

Answer 19

water uptake = water loss

Question 20

how would u set up and use potometer apparatus to ensure no air is present

Answer 20

• cut stem under water
• insert stem under water
• joints must be sealed tight so no air can enter apparatus
• whilst using keep shoot still + open end under water to ensure validity of results

Question 21

why is sucrose transported instead of glucose ?

Answer 21

• sucrose is soluble + metababollicaly inactive

Question 22

similarity + diff between transport in xylem + phloem

Answer 22

simm = both use mass flow + generated hydrostatic pressure
diff = phloem uses living cells xylem does not