Summary
Transport mechanisms in plants involve the movement of water, mineral ions, and organic molecules through different pathways. Water & Mineral Ion Transport — Water and mineral ions are absorbed by roots and transported through the xylem. Example: Water moves by osmosis, while minerals can move by diffusion or active transport. Transpiration — The process of water vapor loss from plant surfaces, mainly through stomata. Example: Water evaporates from mesophyll cells and exits through open stomata. Xerophytic Plants Leaf Adaptations — Adaptations in plants to reduce water loss in arid environments. Example: Thick cuticles and sunken stomata. Movement in the Phloem — Translocation of assimilates like sucrose from source to sink using energy. Example: Sucrose is actively loaded into phloem sieve tubes, creating a pressure gradient. The Sucrose Loading Mechanism — Process involving proton pumps and cotransporter proteins to move sucrose into phloem. Example: H+ ions are pumped out, creating a gradient that facilitates sucrose entry. Phloem: Mass Flow — Movement of phloem sap due to pressure differences between source and sink. Example: Sap moves from high to low pressure areas in the phloem.
Exam Tips
Key Definitions to Remember
- Transpiration: Loss of water vapor from plant surfaces.
- Cohesion-adhesion theory: Explains water movement in xylem due to hydrogen bonds.
- Translocation: Movement of assimilates in phloem from source to sink.
Common Confusions
- Difference between apoplast and symplast pathways.
- Role of stomata in transpiration and gas exchange.
Typical Exam Questions
- What is the main pathway for water movement in high transpiration rates? Apoplast pathway
- How does the Casparian strip affect water movement? It blocks the apoplastic route, forcing water into the symplast.
- What is the role of proton pumps in sucrose loading? They create a gradient for sucrose entry into phloem.
What Examiners Usually Test
- Understanding of water and mineral ion transport mechanisms.
- Explanation of the cohesion-adhesion theory.
- Description of the sucrose loading mechanism and mass flow in phloem.