Transport in PlantsEdexcel GCSE Biology: Revision notes
Section 1
Transport Systems
Xylem (one-way, water/minerals), phloem (two-way, sucrose — translocation).
Xylem=X marks upward only. Phloem=sugars, any direction.
Section 2
Transpiration and Water Movement
Water evaporates from mesophyll cells, diffuses out via stomata, pulling more water up xylem. Water enters roots by osmosis.
Guard cells turgid (water available) = open; flaccid (scarce) = closed.
Section 3
Stomata Structure
Mostly on lower epidermis (reduces water loss); open in day for CO2, close at night.
Section 4
Translocation of Sucrose
Sucrose moves from sources (e.g. leaves) to sinks (e.g. roots, fruit), in any direction — unlike xylem.
Translocation is like a delivery network from factories (sources) to warehouses (sinks).
Section 5
Environmental Factors on Transpiration
Light intensity ↑, temperature ↑, air movement ↑ all increase transpiration rate. Measured with a potometer.
Control all variables except the one being tested.
Section 6
Rate Calculations
Rate = distance ÷ time. Volume = distance × cross-sectional area.
Bubble moves 24mm in 4min: rate=6mm/min. If tube area=0.5mm², volume=12mm³, rate=3mm³/min.
Must Know
- Transpiration: water vapour loss via stomata, drives water uptake.
- Translocation: sucrose sources→sinks, any direction.
- Rate increases with light, temp, air movement.
- Potometer measures water uptake; rate=distance/time.
That's the notes covered.
Carry on to the next subtopic.