Question 1

Which of the following best explains how phytochromes help synchronize a plant's circadian rhythm with the 24-hour day-night cycle?

Accepted Answer

Phytochromes convert Pr to Pfr at dawn, and the daily increase in Pfr resets the plant's internal clock to match the 24-hour cycle.

Question 2

A bean plant has a free-running circadian rhythm of 26 hours. If placed in constant darkness for 72 hours, what will happen to the timing of its leaf movements?

Accepted Answer

The leaves will continue to move, but the timing will gradually shift later each day, becoming desynchronized from the 24-hour cycle.

Question 3

Which of the following statements about photoperiodism in plants is correct?

Accepted Answer

Long-day plants require short nights to flower and will flower if the long night is interrupted by a flash of light.

Question 4

A researcher grafts a long-day plant onto a short-day plant and exposes the grafted plant to short days and long nights. Both the original and grafted parts flower. What does this experiment demonstrate?

Accepted Answer

The flowering signal (florigen) is a mobile protein that can move across grafts and is the same in both long-day and short-day plants.

Question 5

Which of the following best describes the process of thigmotropism?

Accepted Answer

Directional growth of a plant in response to touch, such as tendrils coiling around a support.

Question 6

A Venus flytrap closes its trap when an insect touches its sensory hairs. What is the primary mechanism underlying this rapid movement?

Accepted Answer

An action potential is generated and transmitted from the sensory hairs to the cells responsible for closing the trap.

Question 7

Which hormone is primarily responsible for helping plants conserve water during drought by causing stomata to close?

Accepted Answer

Abscisic acid

Question 8

Mangrove trees survive in waterlogged, low-oxygen soils by producing specialized root structures. What are these structures called, and what is their function?

Accepted Answer

Pneumatophores; they allow oxygen to reach submerged roots.

Question 9

A plant exposed to high soil salinity produces organic solutes to maintain water uptake. Which of the following best explains how this adaptation works?

Accepted Answer

The solutes lower the water potential of the plant cells, making it more negative than the soil, allowing water to enter by osmosis.

Question 10

Which of the following is a correct sequence of events in PAMP-triggered immunity in plants?

Accepted Answer

Recognition of pathogen-associated molecular patterns (PAMPs) → signal transduction → production of phytoalexins

Question 11

A plant is attacked by a pathogen that delivers effectors to suppress PAMP-triggered immunity. The plant responds by activating a local defense that involves programmed cell death around the infection site. What is this response called?

Accepted Answer

Hypersensitive response

Question 12

Which of the following best describes systemic acquired resistance in plants?

Accepted Answer

A plant-wide expression of defense genes, providing long-lasting, nonspecific protection against a variety of pathogens.

Question 13

Which of the following is NOT a typical plant response to herbivore attack?

Accepted Answer

Activation of adaptive immunity involving antibodies.

Question 14

Which of the following best explains why Monstera deliciosa seedlings exhibit skototropism (negative phototropism)?

Accepted Answer

To locate and grow toward the trunk of a tree for support by growing away from the light.

Question 15

Which of the following is a correct description of the action spectrum in plant biology?

Accepted Answer

A graph depicting the relative effectiveness of different wavelengths of radiation in driving a particular process, such as photosynthesis.

Question 16

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

Accepted Answer

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

Question 17

A plant's leaves are restrained in a horizontal position for several days. When released, the leaves move to the position they would have been in if not restrained. What does this demonstrate about the plant's circadian rhythm?

Accepted Answer

The circadian rhythm is controlled by an internal clock that continues even when movement is physically restricted.

Question 18

Which of the following is a correct example of positive and negative gravitropism in plants?

Accepted Answer

Roots growing downward (positive gravitropism) and shoots growing upward (negative gravitropism).

Question 19

Which of the following best describes the role of methylsalicylic acid in plant defense?

Accepted Answer

It is produced at the infection site and transported throughout the plant, where it is converted to salicylic acid to activate systemic acquired resistance.

Plant Responses to Internal and External Signals

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