Mass Transport In Plants Flashcards
1
Q
XYLEM function
A
- transports water and mineral ions through the stem up the plant and to the leaves
2
Q
XYLEM adaptions related to its function
A
- cells joined with no end walls forming a long continuous tube => so enables water to flow as a continuous column
- cells contain no cytoplasm/nucleus so easier water flow/no instructions
- thick cell walls containing lignin so provides support/ withstands tension
- pits inside walls allow later water movements
3
Q
Transpiration
A
- the loss of water vapour from plant leaves by evaporation through the stomata
4
Q
Cohesion tension theory
A
- how water moves up the xylem against gravity via the transpiration stream
5
Q
Cohesion tension theory process
A
- water is lost from the leaf via transpiration
- water evaporates from the mesophyll cells to the air spaces and diffuses though open stomata - this lowers the water potential in mesophyll cells
- so water is drawn out of the xylem down a water potential gradient
- this creates upwards tension on the column of water in the xylem vessels
- Hydrogen bonds result in cohesion between the water molecules
- So water is pulled up as a continuous column
- Water also adheres to the walls of the xylem
- The whole column of water moves up and more water enter the roots via osmosis
6
Q
Factors affecting transpiration rate
A
- light intensity
- temperature
- wind intensity
- humidity
7
Q
Light intensity
A
- Increasing light intensity increase transpiration rate
- this is because more stomata open in the light to let in CO2 for photosynthesis
- allowing more water to evaporate faster
- stomata close when it’s dark due to low transpiration rate
8
Q
Temperature
A
- increasing temperature increases the rate of transpiration
- this is because water molecules have more kinetic energy as temp increase - so water evaporates faster
9
Q
Wind intensity
A
- increasing wind intensity increases the rate of transpiration
- this is because wind blows away water molecules surrounding the stomata
- decreasing water potential of air around the stomata
- therefore increasing the water potential gradient so water evaporates faster
10
Q
Humidity
A
- increasing humidity ( moisture/water in the air) decrease rate of transpiration
- there is more water in the air so it has a higher water potential
- this reduces water potential gradient from leaf to air
- so water evaporates slower
11
Q
Photometer
A
Estimates transpiration rate by measuring water uptake
12
Q
Photometer limitations
A
- does not truly measure transpiration rate as rate of water uptake might not be the same as transpiration rate
- water is used for support/turgidity of plant cells
- water is used in photosynthesis
- water is produced during respiration
13
Q
Phloem
A
- transports organic substances eg. Sucrose in plants
- contains two keys cells:
- seive tube elements
- companion cells
14
Q
Structure of phloem
A
- contains seive tube elements which have no nucleus/few organelles to allow easier flow of organic substances
- also contain end walls called seive plates which allow solutes to pass through
- companion cells are next to seive tube elements and contain lots of mitochondria due to high rate of respiration to produce ATP for active transport of solutes/sucrose
15
Q
Translocation
A
- is the movement of solutes from source to sink through the phloem vessels
- requires energy from ATP
- source : where the solute is made e.g sucrose is made at leaves
- sink : where the solute is used up/converted e.g sucrose is converted to starch by enzymes for storage