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Chapter 6: Problem 10

Explain how the lack of phototropism in an adult plant contributes to the initiation of leaf senescence.

Short Answer

Expert verified
The lack of phototropism in an adult plant hinder the effective absorption of light required for photosynthesis. This leads to a decrease in food and energy production, triggering the plant to initiate leaf senescence to conserve resources.

Step by step solution

01

Define Phototropism

Phototropism is the growth of an organism which responds to a light stimulus. It comes from the Greek words 'photo' - which means light, and 'tropos' - which means turn. In plants, phototropism is an adaptive growth movement where the shoot system bend in the direction of light source. Considering the elliptical shape and lining of auxin (a plant hormone), the part of the shoot exposed to less light grows quicker than the side exposed to more light, causing the shoot to bend towards the light.
02

Define Leaf Senescence

Leaf senescence refers to the final stage of leaf life, it's programmed cell death in plants which incontrovertibly leads to the death of leaf cells. During this process, resources stored in the leaves are mobilized and transported to other parts of the plant, such as growing tissues. It is signalled by environmental factors and internally by plant developmental cues.
03

Link Phototropism and Leaf Senescence

When an adult plant doesn't exhibit phototropism, it means the plant is not bending towards light effectively. Light is essential for photosynthesis - the process by which plants produce food. Therefore, without sufficient absorption of light, photosynthesis is impaired, limiting the production of food and energy. When the food and energy reserves deplete, the plant initiates leaf senescence to conserve resources. In absence of phototropism, more leaves undertake this process at the same time, initiating early leaf senescence.

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Most popular questions from this chapter

Briefly describe the cellular differences between programmed plant senescence and stochastic plant senescence.

Discuss the differences between animal and plant mitotic cell senescence.

The transition from programmed senescence to stochastic senescence can be characterized by the transition from source to sink metabolism. What is meant by the terms source and sink metabolism? What is the role of sink metabolism in the reproductive characteristics of the plant?

Programmed leaf senescence results in a decrease in sucrose concentration in phloem. Does this observation reflect a decrease in the synthesis of intracellular glucose and fructose because of the decline in photosynthesis? Explain.

Describe why the plant cell uses more energy during programmed senescence than during non-senescent, normal cellular function.
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