3.3 transport in plants Flashcards
1
Q
what is the exchange site in plants
A
roots - water and minerals
stomata
pores in older bark
2
Q
adatations of plants to increase sa:v ratio
A
Plants have a branching body shape
Leaves are flat and thin
Roots have root hairs
3
Q
what is mass transport system
A
bulk movement of materials. It is directed movement so involves some source of force
4
Q
why is mass transport important and needed
A
- Bring substances quickly from one exchange site to another
- Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings
- Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
5
Q
whhat are the two seperate mass transport systems in plants
A
- xylem transports water and mineral ions
- phloem transports sucrose and other nutrients
6
Q
why don’t plants ned a specialised trabsport system for oxygen and carbon dioxide
A
- have adaptations that give them a high SA: V ratio for the absorption and diffusion of gases
- leaves and stems possess chloroplasts which produce oxygen and use up carbon dioxide
- low demand for oxygen due to plant tissues having a low metabolic rate
7
Q
function of the xylem
A
- Vascular tissue that carries dissolved minerals and water up the plant
- Structural support
- Food storage
8
Q
where is the xylem and phloem found
A
vascular bundles
9
Q
where is the xylem in the vascular bundle in the root
A
found in the centre and the centre core of this is xylem tissue. This helps the roots withstand the pulling strains they are subjected to as the plant transports water upwards and grows
10
Q
where is the xylem in the vascular bundle in the stem
A
located around the outside and the xylem tissue is found on the inside (closest to the centre of the stem) to help support the plant
11
Q
where is the xylem in the vascular bundle in leaves
A
form the midrib and veins and therefore spread from the centre of the leaf in a parallel line. The xylem tissue is found on the upper side of the bundles (closest to the upper epidermis)
12
Q
function of phloem
A
Transport organic compounds, particularly sucrose, from the source (eg. leaf) to the sink (eg. roots). The transport of these compounds can occur up and down the plant
13
Q
what is the phloem made up of
A
bulk is made up of sieve tube elements which are the main conducting cells and the companion cells
Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres
14
Q
where is the phloem in the vascular bundle in the roots
A
found in the centre and on the edges of the centre core is the phloem tissue
15
Q
where is the phloem in the vascular bundle in the stem
A
located around the outside and the phloem tissue is found on the outside (closest to the epidermis)
16
Q
where is the phloem in the vascular bundle in leaves
A
vascular bundles form the midrib and veins and therefore spread from the centre of the leaf in a parallel line. The phloem tissue is found on the lower side of the bundles (closest to the lower epidermis)
17
Q
what 4 types of cells is the xylem made up of
A
- Tracheids (long, narrow tapered cells with pits) - water conducting
- Vessel elements (large with thickened cell walls and no end plates when mature) - water conducting
- Xylem parenchyma- packign tissue, food storage
- Sclerenchyma cells (fibres and sclereids) - strength and support
most of xylem tisue made up f tracheid’s and vessel elements
18
Q
function of lignified cell walls
A
- spirals of lignin running around the lumen of the xylem
- adds strength to withstand the hydrostatic presure so the vessels dont collapse, impermeable to water
19
Q
function of no end plates
A
allows the mass flow of water and dissolved solutes as cohesive (between water molecules) and adhesive (between water and the walls) forces are ntot impeded
20
Q
function of no protoplasm, cells deaed when mature
A
doesnt impede the mass flow of water and dissolved solutes (transpiration stream)
21
Q
function of pits in walls
A
lateral movement of water, alows continual flow in case of air bubbles forming in the vessels
22
Q
function of small diameter of vessels
A
helps preent the eater column from breakign and assits with capillary action
23
Q
features of the xylem
A
- lignified cell walls
- no end plates
- no protoplasm
- pits in walls
- small diameter of vessels
24
Q
describe how the xylem develops
A
- stem cell specialises into a xylem cell
- lignin is produced around the cell
- ligin production kills the cell as impermeable to water so organelles are broken down
- plasmodesmata form unliginifed pits
- each dead cell becomes a vessel element
25
what cells is the phloem made up of
- Sieve tube elements - main conducting cells
- Companion cells
- Parenchyma for storage and strengthening fibres
- mature phloem tissue contains living cells unlike xylem
26
how are roganic comppounds carried around plants
dissolved in water to form sap
27
features of phloem
- sieve plates with sieve pores
- cellulos cell wall
- no nucleus, vacuole or ribosomes in mature cells
- thin cytoplasm
28
function of sieve plates in phloem
allows for continous movement of organic compounds
29
function of cellulose cell wall in phloem
strengthens the wall to withstand te hydrostatic prssures that move the assimilates
30
function of minimised organelles in phloem
maximises the space for the translocation of the assimilate
31
function of thin cytoplasm in phloem
reduces friction to facilitate the movement of the assimilates
32
what si the role of companion cells in phloem
control the metabolism of their associated sieve tube member, also play a role in loading and unloading of sugars into the phloem
33
features of companion cells
nucleus and otehr organells present
transpor proteins in plasma membrane
large numbers of mitochondria
plasmodesmata
34
function of organelles present in companion cells in
provides metabolic support to sieve tube elements and helps with the loading and unloading of the assimilate
35
function of transport proteins in plsma membrane in companion cells
moe assimilate into and out th sieve tube elements
36
function of large number of mitochndria in companion cells
to provide ATP for the actve transport of assimilates into or out of the cnpanion cells
37
function of plasmodesmata in companion cells
link to siee tube elements whcih allows organic compounds to move from the companion cells into the sieve tube elements
38
comparison of xylem and phloem tissue
living cells: xylem no, phloem yes
substances transpoted: xylem watr and mineral ions, phloem rganic compunds/assimilates
process fo transportation: xylem transpiration, hloem active translocation
direcion of flow: xylem one way/upwards, phloem two ways/up and down
presence of end walls; xylem no, phloem yes
cell wall matrial: xylem lignin ac cellulose, phloem cellulose
39
what is transpiration
refers to the loss of water vapour from a plant to its environment by evaporation and diffusion
Transpiration is a consequence of gaseous exchange at the stomata
40
advatnages of transpiration
provides a means of cooling the plant via evaporative cooling
The transpiration stream is helpful in the uptake of mineral ions
The turgor pressure of the cells (due to the presence of water as it moves up the plant) provides support to leaves (enabling an increased surface area of the leaf blade) and the stem of non-woody plants
41
what causes the movement of water through the xylem
- cohesive and adhesive properties
- graiden tin water potential that parmits the movement of water from osl to atmosphere via plant's cells
42
factors affecting rate of transpiration
- air movement
- temperature
- humidity
- light ntenisty
43
how does air movement affect the rate of transpiration
- There is usually a lower concentration of water molecules in the air outside the leaf
- When the air is relatively still water molecules can accumulate near the leaf surface. This creates a local area of high humidity which lowers the concentration gradient and the rate of transpiration
- Air currents can sweep water molecules away from the leaf surface, maintaining the concentration gradient and increasing the rate of transpiration
44
how does temperature affect the rate of transpiration
- An increase in temperature results in an increase in the kinetic energy of molecules. Therefore an increase in temperature will increase the rate of transpiration as water molecules move out of the leaf (down the concentration gradient) at a faster rate
- If the temperature gets too high the stomata close to prevent excess water loss. This dramatically reduces the rate of transpiration
45
how does humidity affect the rate of transpiration
- If the humidity is high that means there is a large concentration of water molecules in the air surrounding the leaf surface
- This reduces the concentration gradient between inside the leaf and the outside air which causes the rate of transpiration to decrease
- At a certain level of humidity, an equilibrium is reached; there is no concentration gradient and so there is no net loss of water vapour from the leaves
46
how does light intensity affect the rate of transpiration
- Stomata close in the dark, their closure greatly reduces the rate of transpiration
- When the light is sufficient for the stomata to open, the rate of transpiration increases
- Once the stomata are open any increase in light intensity has no effect on the rate of transpiration
- Stomata will remain open at relatively low light intensities
47
graph showing temp on rate of transpiration
| x axi temp
up and down, curve
48
graph showing humidity on rate of transpiration
| x axis: humidity
downwards
49
graph showing air movement on rate of transpiration
| x axis: air moevment
up and plateus, more of a slower inclien and curve
50
graph showing ligth intesnity on rate of transpiration
| x axis: ligth intensity
up and plateus, more of a faster inclien and sharper plateu
51
descreb the root structure
| from outside to most inner
root hair cells
epidermis
cortex
edodermis
pericycle
xylem
phlowm
52
how do water and minerals eneter the roots
- minerals are taken up from the soil by either active transport or diffusion, depending on soil mineral concentrations
- mineral ions lower the water potential of the root hair cells, and water enters the cells from the soil by osmosis
53
what re the 2 pathways to transport water into plants
- apoplastic pathway - diffusion/mass flow
- symplastic - osmosis
54
desrieb the apoplastic pathway
enters the cell wall, travels through the cell walls of epidermis and cortex cells through diffusion, when reaches the endodermis cells the Casparian strip which is waterproof stops the diffusion of water throught the cell wall forcing it to enter the cell by osmosis due to there being a high water potential in the cell walls and low in the cells where it travels through the cytoplasm and plasmodesmata's until it reaches the xylem
55
descrieb the symplastic pathway
Water enters the cytoplasm through the partially permeable plasma membrane.
Water moves into the sap in the vacuole, through the tonoplast.
Water may move from cell to cell through the
plasmodesmata.
Water may move from cell to cell through adjacent plasma membranes and cell walls until it reaches the endodermis and then xylem vessels whcih have pits in walls to allo water in
56
what si the casparian strip
- made of suberin which is impermeable and waterpoof, creates a water tight seal
57
hwo dos water travel in the xylem
- water evaporates from the surface of cells in the leaves, lowering the water potential of leaf cells
- water is drawn out of the xylem and into leaf cells by osmosis down its water potential gradient
- more water molecules are drawn upwards in the xylem in a continuous column due to forces of cohesion between water molecules
- attractive forces of adhesion between water molecules and the sides of the xylem aid this process
58
how does water leave through somata
* The water vapour lost by transpiration lowers the water potential in the air spaces surrounding the mesophyll cells
* The water within the mesophyll cell walls diffuses into these air spaces resulting in a transpiration pull
* This transpiration pull results in water moving through the mesophyll cell wall (apoplastic pathway) or out of the mesophyll cytoplasm (symplastic pathway) into the cell wall
The pull from the water moving through the mesophyll cells results in water leaving the xylem vessels through unlignified pits
59
what are xerophytes
plants that are adapted to dry and arid conditions
60
what are hydrophytes
Plants that are adapted to living in freshwater
61
adaptions of xerophytes
- adapted to maximise water retention
- fleshy suculent leaves stores water for time of low availability
- hinge clls shrink when flaccid, causes leavs to rell epsing thick waterroof cuticel to the air and creates a humid space in middl eo frolled lea
- small surface area of leaves, reduce transpiration due to reuced surface area available
- stomat clsoed during light, open in dqrk, minimise, Transpiration can't take place so no water loss
- sunken stomata/ leaf cered in fine hairs, water loss minimised trapping moist ar close to area of water loss ducign diffusion gradient
- reduced number of stomata, lss water loss due to fewer pores
- stomata only found in upper epidermis, open into humid space created by hairs and rolle shape
- thick waxy xuticel, water los reduced via cuticle
62
adaptations of hydrophytes
- Floating leaves: the leaves are thin, flat and have large air spaces inside to give them buoyancy. This keeps them close to the surface of the water where there is more light for photosynthesis
- Thin waterproof waxy cuticle: it is very thin as there is little need to prevent water loss
- Stomata located on the upper surface of the leaves: this allows for gas exchange to occur with the air instead of the water
- Reduced root system: only small roots are required as they can also extract nutrients from the surrounding water through their tissues
-Reduced veins in the leaves: the xylem is significantly reduced as there is no need to transport water throughout the plant
63
what is a source and sink of assimilates
spurce: source and storage of glucose - green leaves and sten, sorage organs, food stores in seeds
sink: use glucose for growht or respiration - meristems, roots, any part of plant where assimilates are beign stored
64
definition of translocation
refer to the transport of substances in the xylem and phloem, as it means ‘moving from one place to another,’ it is more commonly connected with the transport of assimilates in the phloem tissue
Thus translocation within phloem tissue can be defined as the transport of assimilates from source to sink and requires the input of metabolic energy (ATP)
65
phloem loading
* H+ ions / protons are pumped out of companion cells by active transport creating a concentration gradient
* H+ ions diffuse back into the companion cell down a concentration gradient with sucrose
* This occurs through a co-transporter protein carrier
* This creates a concentration gradient of sucrose between the companion cell and the phloem
- Sucrose diffuses into the adjacent sieve tube element (phloem) through the plasmodesmata
66
describe the pressure flow hypothesis
Active loading of sucrose into sieve tube elements decreases the water potential in the sap;
causing water moves from the xylem down a water potential gradient and into the phloem. This increases the hydrostatic pressure in the phloem at the sources.
At the sinks there is a lower hydrostatic pressure. The sucrose diffuses out of the phloem into the sink (unloaded) where it may be converted to starch and stored or glucose for respiration. This increases the water potential in the phloem. Water moves back out of the phloem into the xylem reducing the hydrostatic pressure.
Due to the hydrostatic pressure gradient from source to sink , the phloem sap moves down the hydrostatic gradient in the sieve tube.
