Chapter 9 Key Concepts Flashcards
The 3 reasons why plants need transport systems
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
how are ROOT HAIRS adapted for their role as an exchange surface?
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
evidence for role of AT in root pressure
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
gas exchange from the leaf
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
evidence for the cohesion tension theory
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
Factors affecting rate of transpiration
-light
-relative humidity
-temperature
split into two sections
-air movement
-soil water availability
how does iincrease light insity affect transpiration
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
-relative humidity how does it affect transpiration
high humidity lowers rate of transp cuz decreased water potential gradient between leaf and outside air
very dry air increases transpiration
-temperature and two ways it affect transpiration
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
-air movement how does it affect transpiration
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
-soil water availability how does it affect transpiration
amount of water in soil can effect transpiration rates
if v. dry
-plant under water stress
-rate of transpiration reduced
main sources of assimilates
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
main sinks
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
evidence for translocation
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.
why use aphids to show evidence of translocation
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
examples of xerophytes
conifes
marram grass
cacti
10 ways xerophytes conserve water
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
how reduced leaves help conserve water
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
how hairy leaves help conserve water
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
how curled leaves help conserve water
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
how leaf loss help conserve water
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
how sunken stomata help conserve water
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
how reduced no stomata help conserve water
reduces water loss by transpiration but also reduce their gas exchange capabilities
how thick waxy cuticle help conserve water
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
how succulents help conserve water
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
how root adaptions help conserve water
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
how avoiding the problem help conserve water
-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
whats so special about the marram grass’s roots
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
examples of hydrophytes
submerged/ free floating -waterlillies -water cress -duckweeds edge -bulrushes -yellow iris
8 adaptations of the hydrophytes
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
Very thin or no waxy cuticle
water loss by tranp not an issue because plenty water avail
many always open stomata on upper surfaces
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
reduced structure to the plant
water supports leaves and flowers so nah need supporting structures
wide flat leaves
to capture as much light as poss
eg water lillies
large SA of stems and roots under water
maximises area for photo and o2 to diffuse into submerged plants
air sacs
enable leaves and or flowers to float to the surface of the water
small roots
less need for uptake by roots as water can diffuse str8 into stem and leaf tissue so less need for uptake by roots
Aerenchyma
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
whats wrong with flooded rice paddies
the aerenchyma provides a low resistance pathway by which methane made from rice plants can be vented to the atmosphere
what happens when there is a lot of water in places like mangrove swaps?
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
