Your friend claims that phloem always carries sugars down a plant. What, if anything, is wrong with that statement?

Compared with a cell with few aquaporin proteins in its membrane, a cell containing many aquaporin proteins willa. have a faster rate of osmosis.b. have a lower water potential.c. have a higher water potential.d. accumulate water by active transport.

Transpiration is fastest when humidity is low and temperature is high, but in some plants it seems to increase in response to light as well. During one 12-hour period when cloud cover and light intensity varied frequently, a scientist studying a certain crop plant recorded the data in the table (top right). (The transpiration rates are grams of water per square meter of leaf area per hour.) Do these data support the hypothesis that the plants transpire more when the light is more intense? If so, is the effect independent of temperature and humidity? Explain your answer. (Hint: Look for overall trends in each column, and then compare pairs of data within each column and between columns.)

A mutant plant lacking the ability to pump protons out of leaf companion cells will be unable to do which of the following?a. initiate transpirationb. load sucrose into sieve-tube elementsc. carry out photosynthesisd. transport water through the xylem

Which of the following would tend to increase transpiration?a. spiny leavesb. sunken stomatac. a thicker cuticled. higher stomatal density

Consider a tree that is 50 m tall and is transpiring roughly 90 liters of water each day. Approximately how many calories will the tree use to transpire this quantity of water?

Salt is used to melt snow and keep roads clear during the winter in many cities. Land adjacent to de-iced roads often ends up with a high concentration of salt in the soil. Explain why plants growing near salted roads may appear wilted in the spring.

Agriculture is by far the biggest user of water in arid western states, including Colorado, Arizona, and California. The populations of these states are growing, and there is an ongoing conflict between cities and farm regions over water. To ensure water supplies for urban growth, cities are purchasing water rights from farmers. This is often the least expensive way for a city to obtain more water, and some farmers can make more money selling water than growing crops. Discuss the possible consequences of this trend. Is this the best way to allocate water for all concerned? Why or why not?

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels?Which of these structural features can help to limit water loss in plants that occupy dry habitats?a. abundant companion cells and sieve-tube elementsb. stomata that are located in pits on the undersides of their leaves, or narrow, needlelike leavesc. extensive networks of xylem and phloemd. stomata that are located on the top surface of leaves, or broadleaves