Question 1

Which of the following best explains why transpiration is considered a 'solar-powered' process in plants?

Accepted Answer

Sunlight causes evaporation at the leaf surface, generating negative pressure that pulls water upward through the xylem.

Question 2

A plant is exposed to a prolonged drought. Which hormone is most likely to be produced in response, and what is its effect on stomata?

Accepted Answer

Abscisic acid; signals guard cells to close stomata, reducing water loss.

Question 3

Which adaptation would you expect to find in a desert plant (xerophyte) to minimize water loss?

Accepted Answer

Stomata located in pits and opening primarily at night (CAM metabolism).

Question 4

Which of the following best describes the mechanism by which guard cells open stomata?

Accepted Answer

Active transport of K$$^+$$ into guard cells decreases water potential, causing water to enter by osmosis and the cells to become turgid.

Question 5

A plant's leaves are wilting on a hot, windy day. Which combination of environmental factors is most responsible for the increased rate of transpiration?

Accepted Answer

High temperature, low humidity, and wind.

Question 6

Which statement about the movement of sugars in plants is correct?

Accepted Answer

Phloem sap moves from areas of high sugar concentration (sources) to areas of low sugar concentration (sinks) by bulk flow.

Question 7

Which of the following best explains why phloem sap can move in different directions in neighboring sieve tubes?

Accepted Answer

The direction of flow depends on the relative positions of sugar sources and sinks served by each sieve tube.

Question 8

Which process is primarily responsible for the positive pressure that drives bulk flow in the phloem?

Accepted Answer

Active loading of sucrose into sieve-tube elements, causing water to enter from the xylem by osmosis.

Question 9

A mature leaf transitions from a sugar sink to a sugar source. What change occurs in its plasmodesmata?

Accepted Answer

Plasmodesmata close or are eliminated, stopping phloem unloading.

Question 10

Which of the following is a real-world example of the pressure-flow hypothesis in action?

Accepted Answer

A fruit tree produces larger fruit when some developing fruits are removed early in the season.

Question 11

Which of the following statements about the symplast is correct?

Accepted Answer

The symplast is a dynamic, living network of cytoplasm connected by plasmodesmata.

Question 12

Which of the following best describes the role of companion cells in phloem transport?

Accepted Answer

They provide metabolic support and facilitate loading and unloading of sugars into sieve-tube elements.

Question 13

Which of the following is NOT a stimulus that typically triggers stomatal opening at dawn?

Accepted Answer

High levels of abscisic acid.

Question 14

Which route describes the movement of sugars from mesophyll cells to sieve-tube elements via plasmodesmata?

Accepted Answer

Symplastic route.

Question 15

Why does water enter sieve-tube elements from the xylem during phloem loading?

Accepted Answer

The water potential in the sieve-tube elements becomes more negative due to high sucrose concentration.

Question 16

Which of the following is a function of the phloem beyond transporting sugars?

Accepted Answer

Systemic transport of hormones, proteins, RNA, and electrical signals throughout the plant.

Question 17

A Venus flytrap closes its leaves rapidly in response to touch. Which plant tissue is primarily responsible for transmitting the electrical signal that triggers this response?

Accepted Answer

Phloem.

Question 18

Which of the following best explains why the concentration of 'free' sugar in a sink is always lower than in the sieve-tube elements?

Accepted Answer

Sugars are immediately converted to starch or used for metabolism in the sink.

Question 19

Which of the following would most likely occur if a plant had more sugar sinks than it could supply with available sugars?

Accepted Answer

The plant would abort some flowers, seeds, or fruits (self-thinning).

Question 20

Which of the following statements about plasmodesmata is correct?

Accepted Answer

Plasmodesmata are dynamic, can open or close, and regulate movement of substances between cells.

Resource Acquisition and Transport in Vascular Plants: Transpiration, Phloem Transport, and Symplastic Dynamics

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