4 interactive labs · AS & A Level Biology 9700
· Find xylem and phloem in root, stem and leaf sections, build a plan diagram and check it, then relate each cell's structure to its job.
Find xylem and phloem in root, stem and leaf sections, build a plan diagram and check it, then relate each cell's structure to its job.
You will be able to
Syllabus learning outcomes: 7.1.1, 7.1.2, 7.1.3, 7.1.4
· Follow water, a wall dye and mineral ions from the soil to the xylem, and find out what the Casparian strip blocks and why.
Follow water, a wall dye and mineral ions from the soil to the xylem, and find out what the Casparian strip blocks and why.
You will be able to
Syllabus learning outcomes: 7.2.1, 7.2.2
· Change humidity, wind, temperature and stomata, watch water vapour leave the leaf and the xylem column move, and measure uptake with a potometer.
Change humidity, wind, temperature and stomata, watch water vapour leave the leaf and the xylem column move, and measure uptake with a potometer.
You will be able to
Syllabus learning outcomes: 7.2.3, 7.2.4, 7.2.5
· Load sucrose with proton pumps and cotransporters, follow mass flow from source to sink, and change the season, the sink and the ATP supply.
Load sucrose with proton pumps and cotransporters, follow mass flow from source to sink, and change the season, the sink and the ATP supply.
You will be able to
Syllabus learning outcomes: 7.2.6, 7.2.7, 7.2.8
Each link is a piece of biology that carries an idea from one lab into another. Follow one to use what you found here in a new setting.
A bean plant grows in soil that dries out over a hot, windy afternoon. Follow the water from the soil to the leaf and work out what happens to its photosynthesis.
The soil solution's water potential falls below that of the root hair cells. Which way does water now move?
Water still moves from higher to lower water potential, so less water, or none, enters the root hair cells; if the soil is lower still, water leaves them.
Transpiration continues from the leaves while uptake falls. What happens to the tension in the xylem water column?
Evaporation from the leaf keeps pulling on the cohesive column, so the tension rises while less water enters at the root: the plant loses water faster than it takes it up and the leaf cells lose turgor.
Abscisic acid reaches the guard cells. What happens to the stomata, and through which signal?
ABA triggers a rise in calcium ions as a second messenger; ions leave the guard cells, their water potential rises, water leaves by osmosis, turgor falls and the stomata close, reducing water loss.
The light is bright but the stomata are now nearly closed. What limits the rate of photosynthesis?
Carbon dioxide concentration inside the leaf falls, so it becomes the limiting factor: brighter light would barely raise the rate.
With less sucrose made in the leaves, what happens to translocation to the roots and seeds?
Less sucrose is loaded at the source, so the hydrostatic pressure gradient to the sinks is smaller and mass flow to them slows.
