plant transport
why do plants need to transport system?
Metabolism demands - All cells of a plant carry out respiration so require glucose and oxygen by photosynthesis
Size - Diffusion is not sufficient to meet the demands
Surface area to volume ratio - Cannot rely on diffusion alone
vascular systems
Xylem and phloem
Root
stem - Arranged in vascular bundles- phloem (top/outside), cambium (middle), xylem (bottem/inside)
leaf
xylem
Nonliving tissue
Transport water and mineral ions from roots to the leaves
no end walls
contains lignin for support
Long hollow tube remains after thickening kills cells
phloem
Transport organic solute from source to sink
Made up of cell stacked and to end
Alive
Each individual cell is a sieve tube element
end walls are sieve plates
Companion cells maintain cell functions
companion cells and sieve tube elements are connected by channels called
Plasmodesmata
water in xylem
Maintains the turgidity
Is a transport medium
root hair cells
- Large surface area for water absorption
- Thin wall for short diffusion distance
- High concentration of solutes in the cytoplasm for low water potential in the cell to maximise the rate of osmosis
to move from root hair cell in epidermis to endodermis water needs to
follow 3 pathways - symplast, apoplast, vacuolar
Xylem transports water up the plants and away from the root - Maintains water potential gradient
symplast
cytoplasm
apoplast
cell walls
vacuolar
vacuoles
suberin (casparian strip)
Waxy layer of waterproof material on cell walls of endoderm cells
what does suberin do (casparian strip)
Forces water from apoplast Pathway into symplast pathway
root pressure
Solutes are actively transported into the xylem which lowers water potential increases volume of water absorbed by osmosis
transpiration
Diffusion of water vapour through the stomata and out of the leaf into the atmosphere
transpiration stream
1. water enters root hair cell by osmosis because of high solid concentration inside
2. Water moves across cortex by osmosis through one of three pathways
3. Water reaches Casperian strip (made of suberin) So it enters the symplast
4. Solutes actively transported into xylem so water follows (root pressure). Water is pulled up the xylem in transpiration stream, using cohesion and adhesion
5. water leaves xylem at the leaves to replace the water vapour that diffuses out of the open stomata by transpiration
effect on rate of transpiration
Light - More photosynthesis, requires more water and CO2, more stomata open, increased transpiration
Humidity - Decrease transpiration, Concentration is lower so slower diffusion
wind speed - Increased transpiration, Increased concentration gradient because of removal of water vapour
Number of open stomata - Increase transpiration, more diffusion
Temperature - kinetic energy increases, Faster transpiration because of increased evaporation
potometer set up
1. Set up underwater (prevent xylem being blocked)
2. Cut the stem at an angle (maximise SA)
3. Use three-way tap or reservoir
4. Use a ruler to measure the movement of the bubble
5. know diameter of glass tube so you can calculate volume
6. Use hairdryer on cold (to stimulate wind), Use warm setting (to stimulate warmer wind)
7. Cover the leaves with Vaseline (adjust leaf SA)
Translocation
The movement of organic solute around a plant in the phloem
movement in the phloem is due to
Hydrostatic pressure gradient created by water movement within the transport system
Mass flow
1.Sucrose actively loaded into seive tube element, Reduces water potential
2. Water follows by osmosis, Increases hydrostatic pressure
3. Water moves down sieve tube down a hydrostatic pressure gradient
4. Crisis removed from sieve tube, increases water potential
5. Water moves out, reduces hydrostatic pressure
loading
Movement of assimilates into sieve tubes
Active or passive
passive loading
symplast
sucrose moves via cytoplasm
Water falls by Osmosis, increases hydrostatic pressure
Active loading
apoplast
Through cell walls
Active loading process
1. H+ Ions are pumped out of companion cells (Active transport)
2. H+ Ions can only re-enter companion cell if they use sucrose transporter (Facilitated diffusion)
3. Sucrose moves down concentration gradient through plasmodesmata into sieve tube
4. Water followed by osmosis, Increases hydrostatic pressure
evidence for translocation
Microscopes see adaptations in companion cells
When respiration Stops translocation stops
xerophytes
Adapted to surviving with limited water ability
Roots are highly developed- Deep tap root or widespread network of roots
Some plants will lose leaves and become dormant when light levels are low
xerophyte adaptation
thick, waxy cuticle- Minimises water loss
Sunken stomata- Reduces air movement over stomata
Reduced numbers of stomata- reduces places where water vapour can escape
hairy leaves- Reduces airflow over leaf
hydrophyte adaptation
No waxy cuticle- No need for plant to conserve water, so energy isnt used to produce cuticle
Many stomata- Maximise rate of gas exchange
Wide flat leaves- Increase the surface area for light absorption
Small roots- Water can diffuse directly into stem and leaves