Chapter 36

Which of the following is an adaptation that enhances the uptake of water and minerals by roots? (A) mycorrhizae (B) pumping through plasmodesmata (C) active uptake by vessel elements (D) rhythmic contractions by cells in the root cortex

A plant cell with a \(\Psi_{\mathrm{s}}\) of -0.65 MIPa maintains a constant volume when bathed in a solution that has a \(\Psi_{\mathrm{s}}\) of \(-0.30 \mathrm{MPa}\) and is in an open container. The cell has a (A) \(\Psi_{\mathrm{P}}\) of \(+0.65 \mathrm{MPa}\). (B) \(\Psi\) of \(-0.65 \mathrm{MPa}\). (C) \(\Psi_{\mathrm{p}}\) of \(+0.35 \mathrm{MPa}\). (D) \(\Psi_{\mathrm{p}}\) of \(0 \mathrm{MPa}\).

Compared with a cell with few aquaporin proteins in its membrane, a cell containing many aquaporin proteins will (A) have a faster rate of osmosis. (B) have a lower water potential. (C) have a higher water potential. (D) accumulate water by active transport.

Which of the following would tend to increase transpiration? (A) spiny leaves (B) sunken stomata (C) a thicker cuticle (D) higher stomatal density

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 \(50 \mathrm{mM}\) NaCl. Assuming that the \(\mathrm{NaCl}\) 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: $$ \Psi_{\mathrm{s}}=-i \mathrm{CRT} $$ where \(i\) is the ionization constant \((2\) for \(\mathrm{NaCl}), C\) is the molar concentration ( \(\ln \mathrm{mol} / \mathrm{L}), R\) is the pressure constant \([R=0.00831(\mathrm{~L} \cdot \mathrm{MPa}) /(\mathrm{mol} \cdot \mathrm{K})],\) and \(T\) is the temperature in Kelvin \(\left(273+{ }^{\circ} \mathrm{C}\right)\) How would this change in the solute potential of the soil affect the water potential of the soil? In what way would the change in the water potential of the soil affect the movement of water in or out of the roots?

Cotton plants wilt within a few hours of flooding of their roots. The flooding leads to low-oxygen conditions, increases in cytosolic \(\mathrm{Ca}^{2+}\) concentration, and decreases in cytosolic pH. Suggest a hypothesis to explain how flooding leads to wilting.

Natural selection has led to changes in the architecture of plants that enable them to photosynthesize more efficiently in the ecological niches they occupy. In a short essay \((100-150\) words \(),\) explain how shoot architecture enhances photosynthesis.

Imagine yourself as a water molecule in the soil solution of a forest. In a short essay (100-150 words), explain what pathways and what forces would be necessary to carry you to the leaves of these trees.