Mass Transport In Plants Flashcards
Root structure
Root hair, Epidermis, cortex, endodermis and xylem
Root hair adaptations
Hair like extensions which increase their surface area to increase uptake of water and increase area for channel on carry proteins so ions can be absorbed
Thinner cellulose cell wall so have shorter diffusion distance
Water uptake from the soil
Root hair cells actively transport ions using ATP across their membrane via carrier proteins
This lowers the water potential of the cytoplasm compared to the water potential in the soil
Water enter the root hair by osmosis down a water potential gradient
Water then passes through the epidermis across the cells of the cortex across the endodermis and into the xylem vessels
The xylem vessels transport water and ions up the plants stems to the leaves
Xylem structure and function
That cells the form hollow tubes with no cytoplasm= faster water flow and less resistance
Continuous tube with no end walls= so continuous column of water can form
Cell walls are strengthened with lignin = this makes the xylem waterproof and rigid to withstand tension and enables adhesion of water
Xylem pits= little holes which allow water to move laterally and can get around blocked vessels
Transpiration ( cohesion tension theory)
Stomata open to enable carbon dioxide to enter the leaf photosynthesis, this causes water to diffuse from the air spaces at a higher water potential inside the leave to a wall lower water potential outside a leaf which is known as an transpiration
This loss of water from the air spaces causes water to move down a water potential gradient from the mesophyll cells to the air spaces
This lower the water potential of mesophyll cell so water moves by osmosis from a adjacent mesophyll cells
This set up a water potential gradient and water is pulled up under tension through the xylem from the roots
Water forms a continuous column in the narrow xylem vessels
Water molecules form, weak hydrogen bonds which stick together and have cohesion
They are attracted to the cell walls of xylem which is known as adhesion
The movement of water is known as a transpiration stream
Factors factor rate of transpiration
Light intensity= stomata open in the light and closed in the dark by God cells increasing in volume
Temperature= increase rate of kinetic energy increase rate of diffusion or more evaporation of water
Humidity= decreases rate of transpiration as decreased water potential gradient as air spaces are saturated with water
Wind speed= water vapour moves away from stomato pores which increases water potential gradient
Stomatal density= increase total number of stomato in a given area of higher rate of transpiration
Measuring rate of transpiration
Rate = length x pie x radius^2 / time
Give precaution the student should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot?
Cut diagonally underwater= prevents damage to the xylem and ensure continuous column of water
Prevent water getting on leaves= prevent loss of water vapour
Potomter is filled with water, making sure that no air bubbles, using a rubber tube which is airtight= prevent entering asylum and shows a continuous column of water
Limitations
Volume of water taken up is equal to loss of water through transpiration but plants also use water for photosynthesis and hydrolysis reactions
Phloem tube structure
transports organic solutes( dissolved substances) mainly sucrose around plants
Sieve tube elements have living cells they have no nucleus and a few organelles they form the tube
Sieve tubes are connected to each other through sieve plate
Each sieve tube element has its own companion cell
Companion cells contain many mitochondria to synthesise ATP through aerobic respiration for active transport of solutes
Mass flow hypothesis
At the source( high concentration of solute / where it’s made )
Companion cells actively transport sucrose into sieve tubes of the flow at the source
This lowers the water potential in the sieve tubes
Water enters the sieve tubes by osmosis from xylem
This creates a high hydrostatic pressure inside the seive tubes at the source at the end of the phloem
At the sink ( used up )
Sucrose is actively transported from the sieve tube into the sink cells to be converted into starch or respired
This increases the water potential inside the sieve tube elements so water leaves the tubes by osmosis
This lowers the hydrostatic pressure inside the seive tubes
Mass flow
This forms a pressure gradient from the source end to the sink end
This gradient pushes saw used towards the sink
When they reach the sink, the solute will be used in respiration or stored as starch
The higher concentration of sucrose at the source, the higher the rate of translocation
Other hypotheses
Ringing experiment= if a ring of bark, including the flow is removed from the Woody stem a bulge forms above the ring.
Radioactive traces
APHIDV they pay the flow then their bodies are removed, leaving the mouth parts behind which allows to sap to flow through
