Chapter 39: Plant Responses to Signals

Increasing the proportion of unsaturated fatty acids in their membranes is a response of plants to __________.

cold stress

Local cell and tissue death often occurs at or near an infection site in a plant. This response is called the _________.

hypersensitive response

The abscission layer __________.

is where a leaf separates from a stem

In shoots, branching is inhibited by __________ from the tip of a growing shoot, but this effect is countered by __________ from the roots.

auxin; cytokinins

A physiological response to alternating light and dark cycles in plants is called _________.

photoperiodism

All of the following functions regarding the plant hormone auxin are correct except _______.

fruit ripening

Growing plant shoots and roots respond to gravity and thus grow either to or away from it. This phenomenon is known as _________.

gravitropism

The signaling molecule for flowering might be released earlier than usual in a long-day plant exposed to flashes of __________.

red light during the night

You have just cut some flowers from your garden. Which of the hormones listed could you apply to the flowers to keep them fresh?

Cytokinins

Some seeds require light for germination. This process is controlled by the phytochrome system. Of the following germination treatments, which would inhibit germination of such seeds?

Exposure of seeds to red light followed by far-red light

In at least some species of plants, a leaf damaged by a caterpillar may __________.

synthesize and release chemicals that attract wasps that prey on the caterpillar

Morphological adaptations in plants for growing in darkness are collectively referred to as __________.

etiolation

Unripe avocados that you purchased at the grocery store ripened quickly in your kitchen when you placed them next to overripe bananas. How did this ripening occur?

The overripe bananas released ethylene, which encouraged the avocados to ripen quickly.

Plants respond to salt stress by _________.

producing organic solutes that adjust the water potential inside the cells

A callus will develop roots if you use a __________ auxin concentration and a __________ cytokinin concentration in the medium.

high; low

Growth that results in curvatures of whole plant organs toward or away from stimuli is called __________.

a tropism, which includes gravitropism, phototropism, thigmotropism, and heliotropism

Which of the following statements is/are correct regarding the effect of blue light on plants?

All of the listed responses are correct.

Light triggers many key events in plant growth and development. This process is known as ________.

photomorphogenesis

The immediate, direct effect of auxin in cell elongation, according to the acid growth hypothesis, is to __________.

activate ATP-driven proton (H+) pumps

An Alaskan trapper worried about being attacked by grizzly bears left the lights on in his cabin all the time. Plants just outside the cabin flowered a month early. Which of the following best explains this?

They must have been long-day plants.

All of the following are plant responses to herbivory except ________.

the production of ethylene

Which of the following statements correctly describes one difference in flowering between short-day plants and long-day plants?

Short-day plants flower when night exceeds a critical dark period, and long-day plants flower when night is shorter than a critical dark period.

Seeds of many desert plants will not germinate until a heavy rain washes away their __________.

abscisic acid

What happens immediately after a phytochrome is activated by light?

Ca2+ channels are opened and guanylyl cyclase is activated.

How may a plant respond to severe heat stress?

By producing heat-shock proteins, which may protect the plant's proteins from denaturing

Which of the following statements correctly matches the plant hormone with its function(s)?

Gibberellins stimulate stem elongation, pollen development, and pollen tube growth.

The formation of air tubes in submerged roots is an adaptation to __________.

oxygen deprivation

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

14 hours light/10 hours dark

You have a plant that is growing taller but is not growing any lateral stems, and you want it to be fuller with more lateral growth, so you remove the apical bud. How would does removing the apical bud lead to more lateral growth in the plant?

Removal of the apical bud removes auxin from the plant, which has the effect of inhibiting lateral growth and allowing cytokinins to flow more freely in the plant, thereby encouraging lateral growth.

Imagine that you have a plant from which you want to produce cuttings so that you have more individual specimens of the plant. Which of the following plant hormones would you apply to the cut stems in order to facilitate their survival?

Auxin