Water transport in plants

Question 1

Transport systems in plants

Answer 1

No circulatory system

Question 2

Locations of phloem and xylem in stem and root

Answer 2

Phloem, xylem, big circle to support plant

Phloem, xylem, small circle to resist pulling forces

Question 3

Water transport in plants

Answer 3

Used for photosynthesis, turgor, rest evaporates

Transpiration, leave evaporation

Question 4

Movement through roots

Answer 4

Symplast pathway

Apoplast pathway

Question 5

Symplast pathway

Answer 5

Water absorbed into RHC, osmosis, decreased WP in root
Diffuses from epidermis through roots to xylem down potential gradient
Cytoplasm in root connected by plasmodesmata through cell wall holes, no further membranes to cross until water reaches xylem, no more osmosis

Question 6

Apoplast pathway

Answer 6

Thick and open cell walls, water diffuses through cell walls
Do not cross membranes by osmosis
Pathway stops at endodermis due to waterproof casparian strip, seals cell walls
Enters symplast pathway
Plant has some control over xylem, water uptake

Question 7

Movement of water into xylem

Answer 7

Active transport of salts with endodermal cells into xylem, along carrier proteins
Decrease in WP, osmosis along pot grad, water moves in

Question 8

Transpiration

Answer 8

Water moves through plants from high WP in soil to low WP in air
Transpiration provides force that pulls water up xylem
Explained by cohesion tension theory

Question 9

Movement through stem

Xylem structure

Answer 9

Composed of dead cells joined together = tubes, no osmosis
Lignin cell wall, laid down in helices, strengthen vessels, do not collapse under pressure
Make woody stems strong
Continuous pipes from root to leaves
Driving movements, transpiration

Question 10

Cohesion tension theory

Answer 10

Water evaporates from mesophyll cell in leaf into air spaces, reduce WP in cells by xylem
Water enters cells from xylem by osmosis
More water molecules drawn up as result of cohesion
Water pulled by xylem due to transpiration
Transpiration put water column under tension

Water adheres to xylem walls
Water column under tension by evaporation from leaves
Strong lignin walls stop collapse under suction pressure
Shrink slightly during day, transpiration at max

Question 11

Movement through leaves

Answer 11

Xylem vessels form leaf veins
Water diffuses from xylem in veins through adjacent cells, lower WP
Symplast pathway through living cytoplasm
Apoplast pathway through non living cell walls
Water evaporates from spongy cels into sub stomata air space, diffuse out through stomata
Endothermic evaporation by solar energy

Question 12

Factors affecting transpiration

Answer 12

Light
Temperature
Air movement
Humidity

Question 13

Potometer equation

Answer 13

Rate of uptake = air bubble speed x cross section area of capillary tube

Question 14

How does a potometer work?

Answer 14

Measures rate of uptake by cut stem
Water used in turgor and photosynthesis
During day, more transpiration and wilt
During night, less transpiration, turgid

Question 15

Effect of light on rate of transpiration

Answer 15

Stimulate stomata open for gas exchange, photosynthesis, increase rate
Wilt with net water loss

Question 16

Effect of temperature on rate of transpiration

Answer 16

Increase temperature, increase rate from spongy mesophyll

Question 17

Effect of air movement on rate of transpiration

Answer 17

Wind blows away saturated air from around stoma, replace with dry air
Increase WP grad, increase rate

Question 18

Effect of humidity on rate of transpiration

Answer 18

Increase humidity, increase WP in air, reduce water potential gradient, decrease rate

Question 19

Limiting water loss in plants

Answer 19

Control stomata to prevent net water loss

Waterproof waxy cuticle

Question 20

Mesophytes

Answer 20

Adequate water

Rhododendron

Question 21

Xerophytes

Answer 21

Dry habitatas

Marramgrass, cacti

Question 22

Halophytes

Answer 22

Salty habitat

Seaweed

Question 23

Hydrophytes

Answer 23

Freshwater habitat

Lilies

Question 24

Xerophytic features

Answer 24

Thick cuticle
Small leaf SA
Low stomata density
Stomata on lower leaf surface
Shedding leaves in dry/cold season
Sunken stomata
Stomatal hairs
Folded leaves
Succulent leaves and stem
Extensive roots

Question 25

Thick cuticles

Answer 25

Stop uncontrolled evaporation through leaf cells

Dicots

Question 26

Small leaf SA

Answer 26

Less area for evaporation

Conifer needles, cactus spines

Question 27

Low stomata density

Answer 27

Fewer gaps in leaves

Question 28

Stomata on lower leaf surface

Answer 28

More humid air on lower surface, less evaporation

Dicots

Question 29

Shedding leaves in dry/cold season

Answer 29

Reduce water loss at certain times of the year

Deciduous plants

Question 30

Sunken stomata

Answer 30

Maintains humid air around stomata

Marramgrass

Question 31

Stomatal hairs

Answer 31

Maintains humid air around stomata

Marramgrass

Question 32

Folded leaves

Answer 32

Maintain humid air around stomata

Marramgrass

Question 33

Succulent leaves and stem

Answer 33

Stores water

Cacti

Question 34

Extensive roots

Answer 34

Maximise water uptake

Cacti

Question 35

Evidence supporting cohesion tension theory

Answer 35

Change in diameter in tree trunks according to rate of transpiration
more tension in xylem, rate is greatest. Pulls wall of xylem inwards, causes trunk to shrink, diameter decreases
If xylem broken, air enters. Tree cannot draw up water as continuous column broken, no cohesion
If xylem broken, water does not leak, not under pressure, most be tension