1. The diagram below shows xylem (on the left) and phloem tissue (on the right) in a stem. Arrows show the direction of movement of water (gray arrows) and sugar (black arrows). Using your knowledge of water potential, solute potential, and pressure potential, fill in the blanks with the missing terms (? water, ? solute, ? pressure) on the diagram in a way that produces the osmotic differences that can drive the circular flow of water from xylem in the root, to phloem in the leaf, back to xylem in the root. HINT: the numbers must add up properly within each equation and the water potentials at each end of each tissue type must produce the flow of water in the correct direction.

Cell A ? =-0.8 ? s=-0.1

Cell B ? =____ ? s=-0.1 ?p=-0.5

Cell C ? =-1.0 ? s=____ ?p=0.7

Cell D ?=____ ? s=-0.7 ?p=0.3

In which cell (A, B, C or D) is the solute potential most negative?_______

In which cell (A, B. C, or D) is the pressure potential most positive?_______

If osmosis generally produces movement of water from a region of higher water potential to a region of lower (more negative) water potential, how does can liquid flow against this water potential gradient in the phloem diagram shown here? THE DIAGRAM IS A GENERIC PICTURE OF THE FLOW OF SUCROSE THROUGH THE XYLEM AND PHLOEM. HIGHER SUCROSE AT THE TOP OF THE XYLEM AND FLOW-LOWER ON THE BOTTOM

Explain how the water potentials in xylem and phloem at the top of the plant can explain the flow of water from xylem to phloem in a leaf.