7.8 - Water Transport in Plants Flashcards
How water moves through a plant The cohesion-tension theory How transpiration relates to gas exchange How to use a potometer to estimate transpiration rate (18 cards)
How does water enter a plant?
Through What and by What process
Through root hair cells via osmosis
How does water move through a plant?
5 steps
- Water enters a plant’s root hair cells via osmosis.
- It moves through the cell cytoplasm or cell walls towards the xylem.
- The xylem transports water from the roots up to the leaves.
- Water is used for photosynthesis.
- Some water evaporates from leaf cells by transpiration and diffuses out of the plant.
What theory explains how water moves up the xylem?
Cohesion-tension theory
What is cohesion?
Hydrogen bonding causes water molecules to stick together
What is adhesion?
Hydrogen bonding between water and xylem walls pulls water upwards
What is transpiration pull?
Evaporation creates tension transmitted down water column
What is transpiration?
Evaporation of water from aerial plant parts
Why does transpiration occur?
4 steps
- Water evaporates (changes from liquid water into gaseous water vapour) from the moist surfaces of mesophyll cells.
- Stomata open so they can absorb carbon dioxide for photosynthesis.
- This provides a pathway for water vapour loss through the open stomata.
- Water vapour moves down a water potential gradient from the air spaces in the leaf into the atmosphere.
What factors affect transpiration rate?
- Light intensity
- temperature
- humidity
- wind speed
How does light intensity affect transpiration?
High intensity opens stomata increasing rate
How does temperature affect transpiration?
High temperature increases evaporation increasing rate.
How does humidity affect transpiration?
Low humidity increases water vapour gradient increasing rate.
How does wind speed affect transpiration?
High wind speed increases water vapour gradient increasing rate.
What is a potometer used for?
Measure rate of transpiration
What are the steps in using a potometer?
8 steps
- Cut the shoot underwater at slant to increase the surface area for water uptake.
- Assemble the potometer with the shoot submerged in water.
- Keep the capillary tube end of the potometer submerged throughout the experiment.
- Check that the apparatus is airtight.
- Dry the leaves, and give the shoot time to acclimatise.
- Shut the tap,** form an air bubble** and record its position.
- Measure the distance the air bubble moves and the time taken.
- Change one variable at a time and keep everything else constant.
How do you calculate the cross-sectional area of the capillary tube?
πr2
How do you calculate the volume of water uptake?
In the potometer experiment
πr2 x d
How do you calculate the rate of transpiration?
Volume of water uptake / time taken
