Biology: The Dynamic Science

Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter 37

Plant Signals and Responses to the Environment - all with Video Answers

Educators

Chapter Questions

Problem 1

Which of the following plant hormones does not stimulate cell division?
a. auxins
b. cytokinins
c. ethylene
d. gibberellins
e. All stimulate cell division.

Caroline Jones

Caroline Jones

Numerade Educator

Problem 2

Which is the correct pairing of a plant hormone and its function?
a. salicylic acid: triggers synthesis of general defense proteins
b. brassinosteroids: promote responses to environmental stress
c. cytokinins: stimulate stomata to close in water-stressed plants
d. gibberellins: slow seed germination
e. ethylene: promotes formation of lateral roots

Joanna Quigley

Numerade Educator

Problem 3

A characteristic of auxin (IAA) transport is:
a. IA A moves by polar transport from the base of a tissue to its apex.
b. IAA moves laterally from a shaded to an illuminated side of a plant.
c. IAA enters a plant cell in the form of IAAH, an uncharged molecule that can diffuse across cell membranes.
d. IAA exits one cell and enters the next by means of transporter proteins clustered at both the apical and basal ends of the cells.
e. All of the above are characteristics of auxin transport in different types of cells.

Caroline Jones

Numerade Educator

Problem 4

Strigolactones:
a. mainly interact with IAA to regulate apical dominance.
b. function only in roots, where they limit lateral branching.
c. counteract the effects of gibberellin in stimulating stem elongation.
d. attract fungal hyphae to roots and regulate lateral branching.
e. are major hormones in plant defenses.

Caroline Jones

Numerade Educator

Problem 5

Which of the following is not an example of a plant chemical defense?
a. ABA inhibits leaves from budding if conditions favor attacks by sap-sucking insects.
b. Jasmonate activates plant genes encoding protease inhibitors that prevent insects from digesting plant proteins.
c. Acting against fungal infections, the hypersensitive response allows plants to produce highly reactive oxygen compounds that kill selected tissue, thus forming a dead tissue barrier that walls off the infected area from healthy tissues.
d. Chitinase, a PR hydrolytic protein produced by plants, breaks down chitin in the cell walls of fungi and thus halts the fungal infection.
e. Attack by fungi or viruses stimulates the production of phytoalexins having antibiotic properties.

Caroline Jones

Numerade Educator

Problem 6

Which of the following statements about plant responses to the environment is true?
a. The heat-shock response induces a sudden halt to cellular metabolism when an insect begins feeding on plant tissue.
b. In gravitropism, amyloplasts sink to the bottom of cells in a plant stem, causing the redistribution of IAA.
c. The curling of tendrils around a twig is an example of thigmotropism.
d. Phototropism results when IAA moves first laterally, then downward in a shoot tip when one side of the tip is exposed to light.
e. Nastic movements, such as the sudden closing of the leaves of a Venus flytrap, are examples of a plant's ability to respond to specific directional stimuli.

Joanna Quigley

Numerade Educator

Problem 7

Which of the following steps is not part of the sequence that triggers flowering?
a. Cycles of light and dark stimulate the expression of the CONSTANS gene in a plant’s leaves.
b. CO proteins accumulate in the leaves and trigger expression of a second regulatory gene.
c. mRNA transcribed during expression of a second regulatory gene moves via the phloem to the shoot apical meristem.
d. Interactions among regulatory proteins promote the expression of floral organ identity genes in meristem tissue.
e. CO proteins in the floral meristem interact with florigen, a so-called flowering hormone, which provides the final stimulus for expression of floral organ identity genes.

Caroline Jones

Numerade Educator

Problem 8

Which of the following are means by which contact with a specific infectious bacterium or fungus triggers a plant defensive response?
a. A plasma membrane receptor binds to a PAMP.
b. PR proteins begin to break down components of the pathogen cell wall.
c. Systemin binding leads to the synthesis of jasmonate.
d. Resistance proteins bind to bacterial virulence effectors that have entered a plant cell.
e. Salicylic acid molecules are released from the besieged plant cell.

Caroline Jones

Numerade Educator

Problem 9

In the sequence that unfolds after molecules of a hormone such as ABA bind to receptors at the surface of a target plant cell:
a. first messenger molecules in the cytoplasm are mobilized, then G proteins carry the signal to second messengers such as protein kinases, which alter the activity of cell proteins such as IP3.
b. binding activates G proteins, which in turn activate second messengers such as IP3; subsequent steps are thought to involve activation of genes that encode protein kinases.
c. binding activates phospholipase $\mathrm{C}$, which in turn activates G proteins, which then activate molecules of IP3, a step that leads to the synthesis of protein kinases.
d. binding stimulates G proteins to activate protein kinases, which then bind calcium channels in ER; the flux of calcium ions activates second messenger molecules that alter the activity of cell proteins or enter the cell nucleus and alter the expression of target genes.
e. binding activates G proteins, which in turn activate phospholipase $C$; this substance then stimulates the synthesis of second messenger molecules, the second messengers bind calcium channels in the cell's ER, and finally protein kinases alter the activity of proteins by phosphorylating them.

Josee Pacheco

Numerade Educator

Problem 10

Hanging wire fruit baskets have many holes or open spaces. The major advantage of these spaces is that they:
a. prevent gibberellins from causing bolting or the formation of rosettes on the fruit.
b. allow the evaporation of ethylene and thus slow ripening of the fruit.
c. allow oxygen in the air to stimulate the production of ethylene, which hastens the abscission of fruits.
d. allow oxygen to stimulate brassinosteroids, which hasten the maturation of seeds in/on the fruits.
e. allow carbon dioxide in the air to stimulate the production of cytokinins, which promotes mitosis in the fruit tissue and hastens ripening.

Joanna Quigley

Numerade Educator

Problem 11

In nature the poinsettia, a plant native to Mexico, blooms only in or around December. This pattern suggests that:
a. the long daily period of darkness (short day) in December stimulates the flowering.
b. vernalization stimulates the flowering.
c. the plant is dormant for the rest of the year.
d. phytochrome is not affecting the poinsettia flowering cycle.
e. a circadian rhythm is in effect.

Joanna Quigley

Numerade Educator

Problem 12

Synthetic auxins such as $2,4-\mathrm{D}$ can be weed killers because they cause an abnormal growth burst that kills the plant within a few days. Suggest reasons why such rapid growth might be lethal to a plant.

Caroline Jones

Numerade Educator

Problem 13

In some plant species, an endodermis is present in both stems and roots. In experiments, the shoots of mutant plants lacking differentiated endodermis in their root and shoot tissue do not respond normally to gravity, but roots of such plants do respond normally. Explain this finding, based on your reading in this chapter.

Caroline Jones

Numerade Educator

Problem 14

In A. thaliana plants carrying a mutation called pickle (pkl), the primary root meristem retains characteristics of embryonic tissue-it spontaneously regenerates new embryos that can grow into mature plants. However, when the mutant root tissue is exposed to a gibberellin (GA), this abnormal developmental condition is suppressed. Explain why this finding suggests that additional research is needed on the fundamental biological role of GA.

Caroline Jones

Numerade Educator

Problem 15

You work for a plant nursery and are asked to design a special horticultural regimen for a particular flowering plant. The plant is native to northern Spain, and in the wild it grows a few long, slender stems that produce flowers each July. Your boss wants the nursery plants to be shorter, with thicker stems and more branches, and she wants them to bloom in early December in time for holiday sales. Outline your detailed plan for altering the plant's growth and reproductive characteristics to meet these specifications.

Josee Pacheco

Numerade Educator

Problem 16

Tiny, thornlike trichomes on leaves are a common plant adaptation to ward off insects. Those trichomes develop very early on, as outgrowths of a seedling's epidermal cells. Biologists have observed, however, that many mature plants develop more leaf trichomes after the fact, as a response to insect damage. Researchers at the University of Chicago decided to study this phenomenon, and specifically wanted to determine the effects, if any, of jasmonate, salicylic acid, and gibberellin in stimulating trichome development. Keeping in mind that plant hormones often interact, how many separate experiments, at a minimum, would the research team have had to carry out to obtain useful initial data? Do you suppose they used mutant plants for some or all of the tests? Why or why not?

Josee Pacheco

Numerade Educator

Problem 17

Cryptochrome occurs in plants and animals. If it was inherited from their shared ancestor, what other major groups of organisms might also have it?

Caroline Jones

Numerade Educator