Chapter 9 Key Concepts

Question 1

The 3 reasons why plants need transport systems

Answer 1

Metabolic demand

• green parts make glucose and O2, other parts eg roots need it transported to them
• hormones made in one place need to be transported to area they have an effect
• mineral ions absorbed by roots need transport to all cells to make proteins for enzymes and struct of the cells

SA:V
-leaves have large SA V but if you combine the roots, stem, trunks, the plant has a small SA V so cant reply on diffusion alone

Size
-need systems to transport substances up and down from the tip of the roots to the topmost leaves and stems

Question 2

how are ROOT HAIRS adapted for their role as an exchange surface?

Answer 2

microscopic so can penetrate easily between soil particles

each hair has a large SA V and their are thousands on each growing root tip

each hair has a thin surface layer (cw and csm) for quick diff and os

con of solutes in the cyto of rhc maintains wp grad entre soil water and cell

Question 3

evidence for role of AT in root pressure

Answer 3

ox or resp substrate falls and the root pressure falls too

increases with increase temp, decrease with decrease temp. suggesting chemical reactions involved

some poisons eg cyanide affect the mito and prevent atp production. add cyanide to root cells and theres no energy supply, root pressure decreases

guttation
xylem sap exudes from the cut ends of the stems at certain times,
in nature, xylem sap forces out of special pores at the end of the leaves in some conditions eg overnight when transpiration is low

Question 4

gas exchange from the leaf

Answer 4

CO2 diffuses from the air and into the leaf whilsto2 does the reverse

down concentration gradients from the air spaces through microscopic pores called stomata, into the air spaces by diffusion down a concentration gradient.

at the same time water evaporates form the surfaces of the leaf cells and into the air spaces

Question 5

evidence for the cohesion tension theory

Answer 5

when xylem vessel broken eg cut flower stem for your house, most times air drawn in nah water leaking out

when vessel broke and air drawn in, plant can’t move water up the stem no more and the continuous stream of h20 molecules held together by the cohesive forces has been broken

changes in tree diameter, when transp it at its highest at midday, tension of xylem is at its highest, so tree shrinks in its diameter. and vice versa.

*can measure the last point by measuring the circumference of suitable size tree at different times in the day

Question 6

Factors affecting rate of transpiration

Answer 6

-light
-relative humidity
-temperature
split into two sections
-air movement
-soil water availability

Question 7

how does iincrease light insity affect transpiration

Answer 7

light needed for photo
in light stomata open for gas ex needed so increase light intensity increase number of stomata open increasing rate of water vapour in therefore increasing the evap from the surfaces of the leaf.
INCREASING TRANSPIRATION

Question 8

-relative humidity how does it affect transpiration

Answer 8

high humidity lowers rate of transp cuz decreased water potential gradient between leaf and outside air
very dry air increases transpiration

Question 9

-temperature and two ways it affect transpiration

Answer 9

increased temp increases the kinetic energy of water and increases rate of evap from the spongy mesophyll cells into the air spaces of the cell

increase temp increases the concentration of water vapour that the external air can hold so it becomes saturated and thus decreases its relative humidity and water potential

BOTH INCREASE RATE OF TRANSPIRATION

Question 10

-air movement how does it affect transpiration

Answer 10

each leaf has a layer of still air around it trapped by the shape of the leaf and features like hairs on the surface of the leaf

they decrease air movement close to the leaf
water vapour that diffuses out of the leaf sometimes accumulates here

water vapour potential around the stomata increases so reduces diffusion gradient INCREASING RATE OF TRANSPIRATION. so increased wind increases transpiration

Question 11

-soil water availability how does it affect transpiration

Answer 11

amount of water in soil can effect transpiration rates
if v. dry
-plant under water stress
-rate of transpiration reduced

Question 12

main sources of assimilates

Answer 12

green leaves and green stems

food stores in seeds when they germinate

storage organs such as tubers and tap roots that are unloading their seeds at the beginning of a growth period

Question 13

main sinks

Answer 13

roots that are growing or actively absorbing minerals

meristems that are actively dividing

any part of the plant that are laying
down food stores eg developing seeds, fruit or storage organs

Question 14

evidence for translocation

Answer 14

advances in microscopy have allowed us to see the adaptations og#f the companion cell for AT

poison mito and translo stops

flow of sugar in phloem is like 10K times faster que if it was just diff alone

using aphid studies, shows a positive pressure in the phloem that forces sap out the stylet.
-pressure and therefore flow rate in the phloem is lower closer to the sink than the source. so con of sucrose in the phloem sap is also higher near to the source que the sink.

Question 15

why use aphids to show evidence of translocation

Answer 15

they penetrate the plant tissue to reach the phloem with their stylet.

if anaesthetise and remove aphid from stylet, phloem continues to flow out of the stylet cuz pressure from phloem content

Question 16

examples of xerophytes

Answer 16

conifes
marram grass
cacti

Question 17

10 ways xerophytes conserve water

Answer 17

leaves
reduces leaves
hairy leaves
curled leaves
leaf loss

stomata
sunken stomata
reduced number of stomata

thick waxy cuticle
succelents
root adaptations
avoiding the problem

Question 18

how reduced leaves help conserve water

Answer 18

decrease leaf area reduces water loss
eg conifer leaves reduced to thin needles almost circular in cross section with a greatly reduced SA V minimising water lost in transpiration

Question 19

how hairy leaves help conserve water

Answer 19

creating a mircoclimate of still humid air, decreasing water vapour potential gradient
minimising the water loss by transpiration from the surface of the leaf
like the spines of some cacti
eg borage flower
some eg marram have microhairs in the sunken stomata pits

Question 20

how curled leaves help conserve water

Answer 20

reduces water loss by transpiration.
confines all the stomata within a microenviroment of still humid air to decrease diff of water vapour from the stomata
eg marram grass

Question 21

how leaf loss help conserve water

Answer 21

eg palo verde
loses all its leaves in the long dry seasons.
tree and branches turn green and photosynthesis with min water loss to keep it alive

Question 22

how sunken stomata help conserve water

Answer 22

in pits to reduce air movements making a microclimate of still humid air that decreases water vapour potential gradient and reduces rate of transpiration
eg marram grass
cacti
sitka spruce
conifers

Question 23

how reduced no stomata help conserve water

Answer 23

reduces water loss by transpiration but also reduce their gas exchange capabilities

Question 24

how thick waxy cuticle help conserve water

Answer 24

10% water loss usually through the cuticle. so use a particularly thick waxy cuticle to help minimise water loss.
esp in evergreen plants
-helps them survive in hot dry summers and cold winders where hard to absorb h20 from the frozen ground eg in holly in the UK

Question 25

how succulents help conserve water

Answer 25

store water in specialised paranchyma tissue in their stems and roots.

have a fleshy swollen appearance

water stored when plenty and used in droughts.

eg Saicornia spp. which gows on UK salt marches
desert cacti and Aloes including Aloe vera

Question 26

how root adaptions help conserve water

Answer 26

long tap roots that grow deep into the ground so can access water a long way below the surface
- mass of wide spread shallow roots with large SA to abosorb any avail waterbefore rain shower evaps including the giant saguaro

Question 27

how avoiding the problem help conserve water

Answer 27

-lose leaves and become dormant
-die completely leaving seeds to germinate and grow rapidly when rain falls again
-survive as storage organs eg bulbs corms or tubers.
-a few can withstand complete dehydration and recover
appear dead and when it rains, the cells recover
plant becomes turgid and green again
begins to photosynthesise.
*linked to the disaccharide trehaloose, that appears to enable cells to survive unharmed

Question 28

whats so special about the marram grass’s roots

Answer 28

long vertical roots that penetrate deep into sand
mat of horizontal rhizomes which many more roots develop from to make an extensive network that helps to change their envrio and enable sand to hold more water

Question 29

examples of hydrophytes

Answer 29

submerged/ free floating
-waterlillies
-water cress
-duckweeds
edge
-bulrushes
-yellow iris

Question 30

8 adaptations of the hydrophytes

Answer 30

Very thin or no waxy cuticle
many always open stomata on upper surfaces
reduced structure to the plant
wide flat leaves
small roots
Large SA of stems and roots under water
Air sacs
Aerenchyma

Question 31

Very thin or no waxy cuticle

Answer 31

water loss by tranp not an issue because plenty water avail

Question 32

many always open stomata on upper surfaces

Answer 32

maxisied gas ex
no risk to loss of turgor cuz bare water avail. so guard cells are inactive
on the upper surface so incontact with air

Question 33

reduced structure to the plant

Answer 33

water supports leaves and flowers so nah need supporting structures

Question 34

wide flat leaves

Answer 34

to capture as much light as poss

eg water lillies

Question 35

large SA of stems and roots under water

Answer 35

maximises area for photo and o2 to diffuse into submerged plants

Question 36

air sacs

Answer 36

enable leaves and or flowers to float to the surface of the water

Question 37

small roots

Answer 37

less need for uptake by roots as water can diffuse str8 into stem and leaf tissue so less need for uptake by roots

Question 38

Aerenchyma

Answer 38

specialised paranchyma in the leaves, stems and roots of hydrophytes
-has many large air spaces made mostly by apoptosis in normal parenchyma
making the plant
-stems and laves more buoyant
-lost resistance internal pathway for the movement of substance such as oxygen to tissues below the water. helping the plant deal with anoxic conditions in the mud by transporting o2 to tissues

Question 39

whats wrong with flooded rice paddies

Answer 39

the aerenchyma provides a low resistance pathway by which methane made from rice plants can be vented to the atmosphere

Question 40

what happens when there is a lot of water in places like mangrove swaps?

Answer 40

roots can become waterlogged. air not water is in short supply
so special aerial roots called pneumatophores grow up towards the air. these have many lenticels that allow the entry of air into the woody tissue