Module 3.3 Flashcards
Transport in plants
Why do multicellular plants need a transport system
SA:V - diffusion distance is large and not efficient enough
Size
Metabolic rate - plants are not active but sugars cant be absorbed in the roots so must be manufactures - need transport system to move water and minerals up to the leaves and sugars from the leaves to the rest of the plant
structure of xylem
lignified cell walls - waterproof and kills cells so they have no contents also strengthens and prevents collapse/closing
bordered pits - water and mineral ions can move out
no end cell walls - continuous column of water
Phloem sieve tube element structure
Sieve plates - movement of assimilates
No nucleus and very little cytoplasm - space for assimilate mass flow
lined end to end to form sieve tubes
Phloem companion cells structure
many mitochondria - provide ATP for active transport
Large nucleus and dense cytoplasm
carry out metabolic processes for loading of assimilates into sieve tubes
process of transpiration
Water enters leaf through xylem moves y osmosis into spongey mesophyll cells
Water evaporates out of cells
Water vapour in air spaces of the leaves
Higher water vapour concentration inside the leaves
Water vapour diffuses out of the stomata
Environmental factors effecting transpiration
Light intensity
Humidity
Temperature
Water availability
Wind speed
precautions for a potometer
Assemble under water - prevents air bubbles from entering equipment/continuous column of water
Vaseline around bung - all water is going into xylem
Cut stem under water - xylem wont water lock
dry leaves - reduced humidity
What is the apoplast pathway
Water travels in the spaces between cells along the cell walls
carried by mass flow not osmosis
What is the symplast pathway
Water travels through the plasma membrane and into the cytoplasm moving through plasmodesmata between cells
Moves by osmosis
How adhesion helps water move up the plant
Water hydrogen bonds to the lignin in the xylem cell walls
Water does not fall down the xylem and can be pulled up
The xylem is very narrow so the forces can pull water up the vessel
How cohesion helps water move up the plant
Water molecules are hydrogen bonded to each other
1 continuous column that can be pulled upwards
What is the transpiration stream
The loss of water by evaporation from the leaves must be replaced with water coming up the xylem. Because of cohesion as one molecule is lost from the top of the chain the whole column is pulled up (cohesion-tension theory)
Role of the xylem
Transport water and mineral ions from root to leaves
Role of the phloem
Transport sucrose, amino acids and other assimilates around the plant
What is root pressure
The endodermis actively transporting mineral ions into the medulla and xylem draws water in by osmosis. Pressure builds up forcing the water into the xylem and pushing the rest of the column up the xylem
What are xerophytes
Plants adapted to live in dry conditions
What are hydrophytes
Plants adapted to live in lots of water
How large air spaces help hydrophytes
help the leaves float so they are exposed to sunlight and can do gaseous exchange
How stomata on the top of the leaves help hydrophytes
The stomata are in contact with air and not water so gaseous exchange can occur
How rolled leaves help xerophytes
increases the humidity around the stomata by trapping air decreasing transpiration
How spikes for leaves help xerophytes
Reduces surface area for transpiration
How fleshy stems help xerophytes
Can act as water storage
How wide roots help xerophytes
when it does rain they collect more water
How tap roots help xerophytes
Can reach down to ground water
How sunken stomata help xerophytes
Increases humidity and reduce wind around the stomate reducing transpiration
How hair around stomata help xerophytes
capture water vapour and hold it around the stomata increasing humidity and reducing transpiration
What is translocation
An active process requiring ATP for the transport of assimilates especially sucrose around the plant between sources and sinks
What are sources
Areas of the plant that produce assimilates to be transported in the phloem e.g. sucrose produced in the leaves
What are sinks
Areas of the plant that require assimilates transported in the phloem e.g. roots and meristem
Active loading at sources
H+ ions actively transported out of companion cells increasing the concentration outside of the cell and decreasing the concentration inside the cell (concentration gradient)
H+ ions diffuse back into the companion cells through cotransporter proteins which will only allow the movement of hydrogen if it is accompanied by sucrose
Creates high concentration of sucrose in the companion cell than sieve tube
Sucrose diffuses through plasmodesmata into sieve tube elements
Removal of assimilates at sinks
Where sucrose is being used the cells have a lower concentration
Sucrose diffuses into the cells through the plasmodesmata
This makes the water potential higher in the sieve tubes so water moves out
The reduces the hydrostatic pressure at the sinks making assimilates flow towards them
Where are the vascular bundles in the stem
Around the outer edge - provides flexibility and strength to withstand bending forces
Where are the vascular bundles in the leaf
Form the midrib
Where are the vascular bundles in the root
Inside the endodermis in X shape - withstand pulling forces
Adaptations of the xylem
cells aligned end to end to form continuous column
Narrow tubes so water column does not easily break
Bordered pits allow water to move out of the vessels
Lignin in patterns allows the xylem to stretch with growth and bend
Role of the endodermis
mineral ions are actively transporting into the medulla and xylem - water potential decreases - water osmoses into the medulla and xylem
Contains the casparian strip
Role of the casparian strip
suberin strip around the outside of endodermis cells which acts as a water proof barrier
Stops the apoplast pathway to ensure all the water travels into the medulla and xylem vessels
How thick waxy cuticles help xerophytes
Reduce evaporation from the leaves
How dense spongey mesophyll helps xerophytes
Less surface area for the evaporation of water
How sucrose moves along the phloem
Mass flow
caused by different hydrostatic pressures at either ends of the tube.
sinks have low HP sources have High HP
