(a) Which of the three community locations was least like the other two?

(b) Rank the three variables (community location, developmental stage of roots, and soil type) in terms of how strongly they affect the "species" composition of the bacterial communities.

Large brown algae called kelps can grow as tall as 25 m. Kelps consist of a holdfast anchored to the ocean floor, blades that float at the surface and collect light, and a long stalk connecting the blades to the holdfast. Specialized cells in the stalk, although nonvascular, can transport sugar. Suggest a reason why these structures analogous to sieve-tube elements might have evolved in kelps. Explain your thinking.

A Minnesota gardener notes that the plants immediately bordering a walkway are stunted compared with those farther away. Suspecting that the soil near the walkway may be contaminated from salt added to the walkway in winter, the gardener tests the soil. The composition of the soil near the walkway is identical to that farther away except that it contains an additional 50 mM NaCl. Assuming that the NaCl is completely ionized, calculate how much it will lower the solute potential of the soil at $20^{\circ} \mathrm{C}$ using the solute potential equation:

$$\Psi_{\mathrm{S}}=-i C R T$$

where i= the ionization constant $(2$ for $\mathrm{NaCl}), C=$ the molar concentration (in mol/L), $R=$ the pressure constant $[R=0.00831(\mathrm{~L} \cdot \mathrm{MPa}) /(\mathrm{mol} \cdot \mathrm{K})]$, and T= temperature in kelvin $\left(273+{ }^{\circ} \mathrm{C}\right)$. Describe how this change in the solute potential of the soil would affect the water potential of the soil. Explain how the change in the water potential of the soil would affect the movement of water in or out of the roots.

In this leaf, what is the maximum number of cells any mesophyll cell is from a vein?

Based on the data, does the initial uptake of water by radish seeds vary wit h temperature? What is the relationship between temperature and water uptake?

Why is the study of the rhizosphere critical to understanding plant nutrition?

How did the evolution of xylem and phloem contribute to the successful colonization of land by vascular plants?

The pathogenic fungus Fusicoccum amygdali secretes a toxin called fusicoccin that activates the plasma membrane proton pumps of plant cells and leads to uncontrolled water loss. Suggest a mechanism by which the activation of proton pumps could lead to severe wilting.

How is the relationship between legume plants and Rhizobium bacteria mutualistic?

How does the Casparian strip force water and minerals to pass through the plasma membranes of endodermal cells?

A scientist adds a water-soluble inhibitor of photosynthesis to roots of a transpiring plant, but photosynthesis is not reduced. Why?

Why is long-distance transport important for vascular plants?

Why do aspen leaves quake?

With your finger, trace the progression of leaf emergence. What is the pattern?