Question 1

Which of the following best describes the main difference between tracheids and vessel elements in xylem tissue?

Accepted Answer

Vessel elements are shorter and wider than tracheids, and have perforation plates for more efficient water flow.

Question 2

A plant is exposed to drought conditions. Which hormone is most likely to be produced to induce stomatal closure, and what is the primary effect on guard cells?

Accepted Answer

Abscisic acid (ABA); guard cells lose water and become flaccid

Question 3

Which of the following best explains why water moves upward through xylem vessels in tall trees?

Accepted Answer

Transpiration creates a negative pressure that pulls water upward, aided by cohesion and adhesion.

Question 4

Which of the following equations correctly represents the water potential ($$\Psi) in $$plant cells?

Accepted Answer

$$\Psi = \Psi_s + \Psi_p$$

Question 5

Aphids are used by scientists to study phloem sap composition. What property of phloem allows sap to ooze out when an aphid's stylet is left in the plant?

Accepted Answer

Phloem is under positive pressure due to turgor pressure from active loading of sugars.

Question 6

Which of the following best describes the function of companion cells in the phloem?

Accepted Answer

They carry out metabolic functions necessary to maintain the sieve tube members.

Question 7

Which of the following scenarios would most likely result in the closing of stomata?

Accepted Answer

High temperature above 34$$^\circC $$and water stress

Question 8

In the pressure-flow hypothesis of phloem transport, what is the main driving force for the movement of sugars from source to sink?

Accepted Answer

Turgor pressure generated by osmotic flow of water into sieve tubes at the source

Question 9

Which of the following adaptations would you expect to find in a CAM plant living in a desert environment?

Accepted Answer

Stomata open at night to minimize water loss

Question 10

A plant cell has a solute potential ($$\Psi_s) of$$ $$-0.7$$ MPa and a pressure potential ($$\Psi_p) of$$ $$0.5$$ MPa. What is the water potential ($$\Psi) of $$the cell?

Accepted Answer

$$\Psi = -0.2$$ MPa

Question 11

Which of the following best explains why guttation occurs in some plants?

Accepted Answer

Root pressure forces water out of hydathodes at leaf margins, usually at night when transpiration is low.

Question 12

Which of the following is NOT a function of the xylem?

Accepted Answer

Transport of sugars from leaves to roots

Question 13

If a plant's guard cells lose K$$^+$$ ions rapidly, what will be the immediate effect on the stomata?

Accepted Answer

Stomata will close due to water loss from guard cells

Question 14

Which of the following best describes the direction of phloem translocation?

Accepted Answer

From source to sink, which can vary depending on the plant's needs

Question 15

A scientist measures the rate of transpiration in a plant and finds it increases with wind velocity. What is the most likely explanation?

Accepted Answer

Wind removes the boundary layer of moist air, increasing evaporation from the leaf surface.

Question 16

Which of the following is a correct sequence of events for stomatal opening in response to blue light?

Accepted Answer

Blue light activates proton pumps, K$$^+$$ enters guard cells, water follows by osmosis, guard cells become turgid, stomata open.

Question 17

Which of the following best explains why sieve tube members in phloem must remain alive?

Accepted Answer

They require energy for active transport of sugars during phloem loading and unloading.

Question 18

A plant is placed in an environment with high CO$$_2$$ concentration. What is the most likely response of its stomata?

Accepted Answer

Stomata will close to prevent excess CO$$_2$$ uptake.

Question 19

Which of the following is a real-world example of the cohesion-tension theory in action?

Accepted Answer

Water being pulled up from the roots to the leaves of a tall tree during transpiration.

Transport Systems in Vascular Plants: Xylem, Phloem, and Stomatal Regulation

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