1. Distinguish between simple diffusion, facilitated diffusion, and active transport. Which of these three mechanisms would most probably account for :
(a) Entry of a small lipid-soluble solute;
(b) Extrusion of sodium ions leaked into a cell;
(c) Rapid entry of a neutral hydrophilic sugar;
(d) Accumulation of potassium ions?
2. The Casparian band was encountered earlier with regard to root pressure and again in this chapter with regard to ion uptake. What is the Caparian band and how does it produce these effects?
3. Trace the pathway taken by a potassium ion from the point where it enters the root to a leaf epidermal cell.
4. What are channel proteins and what role do they play in nutrient uptake?
5. What is the Nernst equation and what does it tell us about ion transport ?
6. How does the concept of molecular cross talk pertain to plant cellular ion transport?
7. Describe the concept of apparent free space. What role does apparent free space play in the uptake of nutrient ions?
8. Why is an accumulation ratio grater than 1.0 not necessarily an indication that active transport is involved ?
9. How do mycorrhizae assist a plant in the uptake of nutrient elements?
10. Describe the colloidal properties of soil. How do the properties of colloids help to ensure the availability of nutrient elements in the soil ?