Exam 35: Water and Sugar Transport in Plants

CAM and C₄ plants conduct photosynthesis in ways that allow them to live in drier areas than most C₃ plants can tolerate. The effectiveness of different plants in restricting water loss while still allowing for influx of adequate CO₂ can be compared using the transpiration ratio, which is calculated by dividing the amount of water transpired by the amount of CO₂ fixed by photosynthesis. If a typical transpiration ratio for a C₃ plant is 500, then possible values for CAM and C₄ plants could be

Which of the following supports the finding that sugar translocation in phloem is an active energy- requiring) process?

Irrigation reduces soil quality and rains usually don't. Why?

The mechanisms that regulate the loading of sucrose from the apoplast to the sieve- tube members by sucrose- H⁺ symporters are not well understood. Of the following possible regulatory factors, which is least likely to be of direct importance?

Which cells in a root form a protective barrier to the vascular system where all materials must move through the symplast?

Most biologists consider loss of water from plant tissues to be a negative thing, and, in fact, many plants have features that reduce water loss. Yet, plants still transpire. Which of the following is the least likely explanation for the fact that plants continue to transpire?

Researchers have investigated bidirectional transport in phloem by applying different radioisotope tracers to two source leaves and monitoring a point between the two sources for the presence of the tracers. Which of the following observations would not support the pressure- flow hypothesis? Appearance of the two tracers in

Which of the following is not a net sink for products of photosynthesis in a deciduous angiosperm tree?

Cavitation is defined as the formation of bubbles within a liquid. Based on this definition, which mechanism of water transport in xylem can contribute to recovery from cavitation?

In the pressure- flow mechanism, loading of sucrose from companion cells to sieve- tube elements takes place through

The researchers discovered a new proton pump that is involved in phloem unloading in the sugar storage tissue. Predict the movement of ions carried out by this pump.

Water potential of plants during night is _ compared to day water potential due to .

The pressure- flow mechanism for sugar translocation you have learned about is based on research on angiosperms, and thus might not occur in other vascular plants. Which of the following real or hypothetical observations on gymnosperms would suggest they possess a different mechanism?

Which of the following does not support the cohesion- tension theory of xylem transport?

As an undergraduate research assistant in the lab of the famous Dr. S. Nameerf, your duties involve measuring water potential in experimental soil- plant- atmosphere systems. Assume you make a series of measurements in a system under normal daylight conditions, with stomata open and photosynthesis occurring. Which of the following correctly depicts the trend your measurement data should follow if the cohesion- tension mechanism is operating?

Which of the following features of plant cells allows for apoplastic movement of water?

Compared to plants from other environments, the cells of many desert plants contain high concentrations of solutes. This helps them survive in their arid surroundings because the high solute concentrations create relatively , which help reduce water loss.

Which of the following would not be expected to contribute to high rates of transpiration?

Hypothetical plant cells A and B are adjacent to each other. The solute potential ƒS) of cell A is - 0.35 MPa, and its pressure potential ƒP) is +0.15 MPa. The solute potential ƒS) of cell B is - 0.30 MPa, and its pressure potential ƒP) is +0.05 MPa. In which direction will net water movement occur?

Which of the following is a similarity between xylem and phloem transport?