transpiration

Question 1

define transpiration

Answer 1

loss of water from plants by evaporation

Question 2

define transpiration stream

Answer 2

constant movement of water from roots to the leaves, driven by evaporation from stomata

Question 3

stages of transpiration

Answer 3

water vapour exits the leaves through stomata by transpiration

loss of water creates a pull that draws water up the xylem

water drawn into roots from soil by osmosis, moves up the stem

Question 4

role of stomata

Answer 4

gas exchange
let CO2 in for photosynthesis
let small amount of O2 for respiration

Question 5

control of stomata

Answer 5

photosynthesis, guard cell pump solutes in by active transport
water enters by osmosis, cell become turgid
cellulose hoops stop cells from swelling in width, swell lengthways
inner wall less flexible than outer curve outwards

Question 6

what is a side effect of gas exchange

Answer 6

water mol evaporate from surface of mesophyll cells into air spaces in leaf
move out stomata into surrounding air by diffusion down a concentration gradient

loss of water from mesophyll cell, lower water potential of cell, water move into mesophyll from adjacent cell by osmosis via apoplast

Question 7

adhesion in transpiration

Answer 7

water molecules form H bonds with carbohydrates in xylem walls

Question 8

cohesion in transpiration

Answer 8

water are polar, form H bonds

Question 9

define mass flow

Answer 9

movement of fluids down a pressure gradient

Question 10

what does transpiration pull from mass flow create

Answer 10

tension, lignin need to withstand

Question 11

how can tension successfully pull water to top of plant

Answer 11

column of water inside vessel must be intact
any breaks/bubbles in column would break the cohesion between water mol and prevent upward movement

Question 12

how does xylem overcome bubbles

Answer 12

bordered pits between adjacent vessels, allow lateral movement of water, maintain an intact column or allow column to bypass bubbles

Question 13

evidence for cohesion tension theory

Answer 13

cut flowers - draw air in rather than leaking water out, water continues to move up stem

broken xylem - broken/ cut xylem stop drawing up water as air in breaks transpiration stream - cohesion between water molecules

changes in tree diameter - high transpiration rate, diameter increase bc of tension

Question 14

how can water loss be controlled

Answer 14

waxy cuticle, prevent evaporation from top of leaf

wilting - protection mechanism against further water loss, leave collapse, hand down, smaller SA for evaporation

closed stomata at night

stomata at bottom, lower light intensity

deciduous plants lose leaves in winter- ground may be frozen, temp too low for photosynthesis

guard cells - close pore (little water, low turgor)
pump in solute when favourable

Question 15

list factors affecting transpiration

Answer 15

light intensity
humidity
temperature
air movement
soil-water availability

Question 16

how does light intensity affect transpiration

Answer 16

more light, more photosynthesis, open stomata let CO2 in, more water evaporate, more transpiration

Question 17

how does humidity affect transpiration

Answer 17

high humidity, reduce water vapour potential gradient, less transpiration

Question 18

how does temperature affect transpiration

Answer 18

increase in temp, increase in kinetic energy, more water evaporates, more transpiration

increase in temp, external air can hold more water, greater water vapour potential gradient, more transpiration

Question 19

how does air movement affect transpiration

Answer 19

water vapour is moved away from air surrounding leave, greater water potential gradient, more transpiration

Question 20

how does soil-water availability affect transpiration

Answer 20

dry soil, plant under water stress, less transpiration