Biology · Both
Plant Transport & Transpiration
How water, minerals and sugars move through plants; transpiration and factors that affect its rate.
Plants move water and minerals in xylem and sugars in phloem. Transpiration drives the water stream from roots to leaves.
Xylem and phloem
• **Xylem** – transports water and mineral ions from roots to leaves; dead hollow cells; lignified walls
• **Phloem** – transports dissolved sugars (translocation) from leaves to growing/storage regions; living cells
Root hair cells increase surface area for uptake of water (osmosis) and minerals (active transport).
Transpiration
**Transpiration** – evaporation of water from leaves (mainly through stomata).
Water lost from leaves pulls more water up the xylem (transpiration stream).
Factors that increase rate:
• Higher temperature
• Higher wind speed
• Lower humidity
• Higher light intensity (stomata open)
Worked example
Why does wind increase transpiration rate?
Solution
It blows away water vapour near the leaf, maintaining a steeper concentration gradient so diffusion out of stomata is faster.
Stomata
Pores on the leaf surface controlled by guard cells.
Open to allow CO₂ in for photosynthesis; water vapour also escapes.
Often more numerous on the underside of the leaf.
Practice questions
Try these without looking at the answers first.
Q1.What does xylem transport?
Show answer
Water and mineral ions
Q2.Name three factors that increase transpiration.
Show answer
Temperature, wind, low humidity, light (any three)
Q3.What is translocation?
Show answer
Movement of sugars in the phloem