alleryStart learning →Which characteristic of senescence explains the yellowing of leaves?
AThe breakdown of chloroplasts in the leaf
BThe blocking of xylem by gas embolisms
CThe thickening of the waxy leaf cuticle
DThe loss of turgor within the guard cells
Answer & Solution
Correct answer: A. The breakdown of chloroplasts in the leaf
1. Senescence is the ageing of a plant and the complex biochemical changes that go with it.
2. One of its characteristics is the breakdown of chloroplasts, which shows as the yellowing of leaves.
3. Chloroplasts hold membranes, proteins and DNA of the photosynthetic machinery.
4. Specific enzymes break those proteins, lipids and nucleic acids into smaller molecules.
5. The plant salvages those molecules to support the growth of other tissues.
6. Embolisms and loss of guard cell turgor cause wilting or blocked transport rather than the colour change of an ageing leaf.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 32 "Plant Reproduction", section 32.3 Asexual Reproduction_
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