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Ch. 33 Control Systems in Plants
Taylor - Campbell Biology: Concepts & Connections 10th Edition
Taylor, Simon, Dickey, Hogan10th EditionCampbell Biology: Concepts & ConnectionsISBN: 9780136538783Not the one you use?Change textbook
All textbooksTaylor, Simon, Dickey, Hogan 10th EditionCh. 33 Control Systems in PlantsProblem 4
Chapter 33, Problem 4

In autumn, the amount of _________ increases and the amount of _________ decreases in fruits and leaf stalks, causing a plant to drop fruit and leaves.
a. Ethylene … auxin
b. Gibberellin … abscisic acid
c. Cytokinin … abscisic acid
d. Auxin … ethylene

Verified step by step guidance
1
Step 1: Understand the context of the question. The question is asking about the hormonal changes in plants during autumn that lead to the dropping of fruits and leaves. This process is part of plant physiology and involves plant hormones.
Step 2: Recall the role of ethylene. Ethylene is a plant hormone that promotes fruit ripening and leaf abscission (shedding of leaves). Its levels typically increase in autumn to facilitate these processes.
Step 3: Recall the role of auxin. Auxin is another plant hormone that helps maintain the attachment of leaves and fruits to the plant. Its levels decrease in autumn, which allows ethylene to promote abscission.
Step 4: Analyze the options provided. The correct answer should reflect the increase in ethylene and the decrease in auxin, as these hormonal changes are responsible for the dropping of fruits and leaves.
Step 5: Select the correct answer based on the analysis. The correct choice is 'a. ethylene … auxin,' as it matches the hormonal changes described in the question.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ethylene

Ethylene is a plant hormone that plays a crucial role in the regulation of fruit ripening and leaf abscission. It promotes the shedding of leaves and fruits, especially in response to environmental cues such as changes in light and temperature. In autumn, increased ethylene levels signal the plant to prepare for winter by dropping its leaves and fruits.
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Auxin

Auxin is another important plant hormone that influences growth and development, particularly in elongation and cell division. It helps maintain the connection between the plant and its leaves and fruits by promoting their retention. As auxin levels decrease in autumn, the plant becomes less able to hold onto its leaves and fruits, facilitating their drop.
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Auxin

Abscission

Abscission is the process by which plants shed their leaves, fruits, or flowers. This process is regulated by a balance of hormones, including ethylene and auxin. In autumn, the increase in ethylene and decrease in auxin trigger abscission, allowing the plant to conserve resources and prepare for the colder months ahead.
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Related Practice
Textbook Question
Test your knowledge of the five major classes of plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene) by matching one hormone to each lettered box. (Note that some hormones will match up to more than one box.)

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Textbook Question

During winter or periods of drought, which one of the following plant hormones inhibits growth and seed germination?

a. Ethylene

b. Abscisic acid

c. Gibberellin

d. Auxin

1024
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Textbook Question

Auxin causes a shoot to bend toward the light by

a. Causing cells to shrink on the dark side of the shoot

b. Stimulating growth on the dark side of the shoot

c. Causing cells to shrink on the lighted side of the shoot

d. Stimulating growth on the lighted side of the shoot

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Textbook Question

Plant hormones act by affecting the activities of:

a. Genes

b. Membranes

c. Enzymes

d. Genes, membranes, and enzymes

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Textbook Question

Buds and sprouts often form on tree stumps. Which hormone would stimulate their formation?

a. Auxin

b. Cytokinin

c. Abscisic acid

d. Ethylene

1180
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Textbook Question

Which of the following is a type of defense used by plants to deter herbivores?

a. Chemicals toxic to the herbivore

b. Chemicals that recruit other animals

c. Spines

d. a, b, and c

1186
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