Study Notes
Transport in the xylem involves the movement of water from the roots to the leaves, driven by transpiration and facilitated by the cohesive and adhesive properties of water. Transpiration — the loss of water vapour from plant leaves and stems. Example: Water evaporates from leaves through stomata. Stomata — pores on the leaf surface that allow gas exchange. Example: Stomata open for photosynthesis, increasing transpiration. Cohesion — attraction between water molecules, aiding in water transport. Example: Water molecules stick together, forming a continuous stream in the xylem. Adhesion — attraction between water molecules and xylem walls. Example: Water molecules adhere to xylem walls, helping them move upward. Guard Cells — cells that regulate the opening and closing of stomata. Example: Guard cells become flaccid, closing stomata to reduce water loss. Xerophytes — plants adapted to dry environments. Example: Xerophytes have reduced leaves to minimize water loss. Halophytes — plants adapted to saline conditions. Example: Halophytes sequester salts in vacuoles to tolerate high salinity.
Exam Tips
Key Definitions to Remember
- Transpiration: The loss of water vapour from plant leaves and stems.
- Stomata: Pores on the leaf surface for gas exchange.
- Cohesion: Attraction between water molecules.
- Adhesion: Attraction between water molecules and xylem walls.
- Guard Cells: Cells that control the opening and closing of stomata.
Common Confusions
- Confusing cohesion with adhesion.
- Misunderstanding the role of guard cells in regulating water loss.
Typical Exam Questions
- What is transpiration? Transpiration is the loss of water vapour from plant leaves and stems.
- How do guard cells regulate transpiration? Guard cells open and close stomata to control water loss.
- Why is cohesion important in the xylem? Cohesion helps water molecules stick together, forming a continuous stream.
What Examiners Usually Test
- Understanding of how water is transported in the xylem.
- The role of stomata and guard cells in transpiration.
- Adaptations of plants like xerophytes and halophytes for water conservation.