Module 2 Exchange and Transport

1. Module 2 Exchange and Transport Roots and Translocation

2. Title: Pathway of water & sucrose • Lesson objective: • Can I describe the pathway of water? Grade C • Can I explain translocation? Grade B Starter: Draw a diagram to show a turgid cell and plasmolysed cell…. Label where there is a high water potential and low water potential with an arrow to show movement.

3. Water potential…. This is the tendency of water molecules to move from a high water potential to a lower water potential. Remember: Pure water has the HIGHEST water potential = 0. Cytoplasm contains sugars and salts which lowers water potential.

4. Pathways of water… A – Apoplast pathway – water moves through spaces in the cell walls. B – Symplast pathway – water passes through the plasmodesmata. C – Vacuolar pathway – enter and passes through the vacuole.

5. Root hair cells increase the surface area of the root. Minerals are absorbed by active transport which reduces the water potential of the cytoplasm. Water is then taken up by osmosis as the molecules move down the water potential gradient.

7. In the root…. Endodermis – waxy strip called the Casparian Strip which forces water into the symplast pathway. Ensures water and mineral ions have to pass into the cytoplasm through the cell membrane. Role of Transporter proteins…?

8. How does water move up? • Root pressure – active transport of minerals into xylem drives water into xylem by osmosis. • Transpiration pull – cohesion-tension theory of maintaining an unbroken column of water up the xylem. • Capillary action – adhesion of water molecules to the sides of the xylem vessel.

9. Translocation… The movement of assimilates e.g. sucrose (sugars). The source releases sucrose into the phloem. The sink is where sucrose is removed from the phloem. How: active transport using ATP

10. Active loading at the source

11. Mass flow in the phloem