transpiration Flashcards
(15 cards)
What is transpiration? (2)
Transpiration is the loss of water from the aerial parts of a plant
Mainly through the stomata
Why is transpiration unavoidable for plants? (2)
Stomata must open for gas exchange CO2 in O2 out for photosynthesis
Leading to water loss through the open stomata
What are the steps in water movement during transpiration? (3)
1 Osmosis from xylem to mesophyll cells
2 Evaporation from mesophyll cells to form water vapour in air spaces
3 Diffusion of water vapour through stomata
What factors affect the rate of transpiration? (8)
Number of leaves
Number size and position of stomata
Presence of a cuticle
Light
Temperature
Humidity
Air movement
Water availability
What does a potometer measure? (1)
Measures water uptake which gives an estimate of transpiration
Why are potometer measurements only an estimate of transpiration rate? (2)
Not all water taken up is lost via transpiration
Some is used for photosynthesis and to maintain turgidity
How do you use a potometer to estimate transpiration rates? (6)
1 Cut a healthy shoot underwater
2 Insert the shoot into the apparatus underwater
3 Ensure the apparatus is airtight
4 Dry the leaves and allow the shoot to acclimatise
5 Keep conditions constant except for the variable being tested
6 Measure the distance the air bubble moves per unit time to estimate water uptake
How does water enter a plant? (2)
1 Water enters the plant through root hair cells by osmosis
2 Moving from areas of higher water potential soil to areas of lower water potential inside the plant
How are root hair cells adapted for water absorption? (4)
1 Large surface area for absorption
2 Thin walls for a short diffusion pathway
3 Unlignified permeable to allow entry of water and minerals
4 Low water potential to facilitate water uptake by osmosis
What are the two main pathways for water transport through plants? (2)
Symplast pathway Water moves through the cytoplasm and plasmodesmata by osmosis
Apoplast pathway Water moves through the cell walls by diffusion and mass flow until it reaches the Casparian strip where it is forced into the symplast pathway
What is the role of the Casparian strip in the root? (2)
Blocks the apoplast pathway and forces water to enter the symplast pathway
Before reaching the xylem
How is water transported through the plant in the xylem? (3)
Water is pulled up the xylem by
cohesion - water molecules stick together
Adhesion water sticks to xylem walls
Tension created by water evaporating from the leaves
What is the transpiration stream? (2)
The movement of water from roots to leaves through the xylem
Driven by transpiration and involving cohesion adhesion and tension forces
How are xerophytic plants adapted to reduce water loss? (6)
1 Sunken stomata to trap water vapour and reduce the water potential gradient
2 Hairs around stomata to trap moist air
3 Rolled leaves to trap moist air in windy conditions
4 Thick waxy cuticle to reduce evaporation
5 Spines to reduce surface area for water loss
6 Stomata close during hot conditions
How are hydrophytic plants adapted to survive in water? (3)
Air spaces in tissues to help float and store oxygen
Stomata on the upper surface of floating leaves for gas exchange
Flexible leaves and stems to prevent damage from water currents
