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Ch. 39 - Plant Responses to Internal and External Signals
Chapter 39, Problem 7

A plant mutant that shows normal gravitropic bending but does not store starch in its plastids would require a reevaluation of the role of          in gravitropism. a. auxin b. calcium c. statoliths d. differential growth

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Key Concepts

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

Gravitropism

Gravitropism is the growth response of plants to gravity, allowing them to orient their roots downward and stems upward. This process is crucial for plant stability and nutrient acquisition. It involves the perception of gravitational forces, which is mediated by specialized cells that detect gravity and signal the plant to grow accordingly.
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Statoliths

Statoliths are specialized organelles found in plant cells that play a key role in gravity sensing. These dense, starch-filled structures settle under the influence of gravity, helping the plant determine its orientation. The movement of statoliths within the cell influences the distribution of growth hormones like auxin, which in turn affects the direction of growth.
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Auxin

Auxin is a plant hormone that regulates various aspects of growth and development, including gravitropism. It promotes cell elongation on the side of the plant that is away from gravity, causing the plant to bend towards the gravitational pull. The interaction between auxin distribution and statoliths is essential for the plant's ability to respond to its orientation in space.
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