14. According to the passage, which of the following most directly causes leaves to change their color in the fall?
Answer: D
New chlorophyll no longer being produced
Leaves change color in the fall primarily because new chlorophyll is no longer being produced, which allows other pigments in the leaves to become more visible.
A) Chlorophyll in the leaves beginning to break down then
While the breakdown of chlorophyll does contribute to the color change, it is not the initial cause. The absence of new chlorophyll production is the critical factor that leads to the visibility of other pigments that cause the color change.
B) Heat and light causing new pigments to be produced
This option is incorrect because the change in leaf color in the fall is not due to the production of new pigments. Instead, it results from the existing pigments becoming more noticeable after chlorophyll production ceases.
C) Existing pigments becoming more uniform
The idea of existing pigments becoming more uniform does not accurately describe the process of color change in leaves. The change is due to the cessation of chlorophyll production, which allows the variation in color from other pigments to emerge, rather than a uniformity of existing pigments.
D) New chlorophyll no longer being produced
This option is correct because the stopping of new chlorophyll production leads to a decrease in green color, allowing other pigments such as carotenoids and anthocyanins to show through and create the vibrant fall colors.
Conclusion
The cessation of new chlorophyll production is the definitive cause of leaves changing color in the fall, as it allows the other pigments to become visible. Options A, B, and C fail to address the fundamental reason for the color change, which is directly linked to chlorophyll dynamics. Thus, option D stands out as the most accurate explanation in this context.