1. Transport in Vascular Plants Chapter 36

2. Review: Cell Transport Passive transport: – Diffusion across membrane with concentration gradient, no energy required Active transport: – Pumping of materials against concentration gradient, ATP required May involve transport proteins (ex: proton pump) Cotransport Chemiosmosis

3. Recall: Water Potential The combined effects of solute concentration and physical pressure Determines the direction of movement of water Water moves from areas of high water potential to areas of low water potential Bozeman biology

4. Transport Transport in plants occurs on three levels: – Cellular Absorption of water and minerals from soil by root cells – Short distance Cell-to-cell at tissue level Ex: loading sugar into phloem – Long distance Sap in xylem and phloem throughout plant

5. Transport of Water Moving water up the xylem to the leaves is known as transport There are 3 major parts to the transport of water: – Absorption at the roots – Capillary action up the xylem – Transpiration (evaporation) at the leaves The water also brings nutrients and mineral vital for plant growth with it

6. Step 1: Absorption at the roots Active transport of minerals into root hairs Diffusion to the pericycle Active transport into the vascular cylinder Diffusion into the xylem Mycorrhizal fungi help plants absorb minerals and water Nitrogen fixing bacteria live in nodules of roots to assist in nitrogen uptake

7. Casparian Strip The Casparian strip controls water movement into the vascular cylinder of the root Water cannot move between cells; it must move through the cells by osmosis. Why is this important?

8. Step 2: Capillary Action Due to hydrogen bonds, water molecules stick to one another and other polar surfaces Cohesion and adhesion cause water to climb up xylem as if it were a chain being pulled

9. Cohesion-Tension Theory Cohesion causes molecules to stick to one another As water evaporates, it “pulls” the chain upwards from the roots to the leaves As more water is drawn up the stem, the water pressure in the roots is lowered, therefore, it takes in more water

11. Step 3: Transpiration Evaporation occurs in the leaves Why is this important? This keeps water flowing upward from the roots This is the strongest force involved in water transport Stomata help regulate the rate of transpiration by opening/closing to help balance conservation of water with gas exchange for photosynthesis

12. Sugar Transport Sugar is made in the leaves and plants store it as a mixture of sugar and water called sap Due to the sugar content, plants must move sap against a concentration gradient The leaves (where sugar is made) are called a source Where sugar ends up are called sinks

13. Pressure Flow Theory The pressure flow theory explains how sap moves in a plant from source to sink: – Sugars begin at a source and are pumped into phloem tube cells – Osmosis moves water into the cells and raises pressure – Pressure moves sap

14. Step 1: Getting Glucose Out of Parenchyma The leaf is a source of sugar Glucose and fructose made by photosynthesis are linked to make sucrose Sucrose will need assistance moving across the membranes of cells – Companion cells Companion cell Parenchyma cell

15. Step 2: Using Water to Help Sucrose Move Active transport moves sucrose into the xylem cells As sugar moves in, water will move in also to attempt to reach a state of equilibrium This raises the pressure in the tubes

16. Step 3: Reaching the Sink Active transport will move sugar out of xylem into a sink (like a fruit) As sugar concentration drops, water moves out of the cell, lowering the pressure The lower pressure the more the column of sap will move

17. Pressure Flow Hypothesis