Key facts & rules

• Xylem: transports water and mineral ions from roots to leaves — one-way, dead cells, hollow tubes.
• Phloem: transports sucrose and amino acids from leaves to all parts — two-way, living cells.
• Transpiration: loss of water vapour from leaves through stomata.
• Transpiration rate increases with: higher temperature, lower humidity, increased light, higher wind speed.
• Water enters root hair cells by osmosis (soil water more dilute than cell contents).
• Stomata open in light (guard cells become turgid); close in dark or water stress.
• Wilting: loss of turgor due to water loss — cells become flaccid.