Difficulty: Medium

Average Score: 60%

A turning leaf stays green at first, then reveals splotches of yellow and red as chlorophyll gradually breaks down. Dark green seems to stay longest in the veins, outlining and defining them. During the summer, chlorophyll breaks down in the heat and light, but it is also being steadily replaced. In the fall, on the other hand, no new pigment is produced, and so we notice the other colors that were always there, although chlorophyll's shocking green hid them from view. With their camouflage gone, we see these colors for the first time all year, and marvel, but they were always there, hidden like a vivid secret beneath the hot glowing greens of summer.

According to the passage, which of the following most directly causes leaves to change their color in the fall?

Rationale

Chlorophyll in the leaves beginning to break down then.

As the temperatures drop and daylight hours shorten, chlorophyll in leaves begins to break down, revealing the vibrant colors of other pigments that were previously masked. This process is the primary reason for the change in leaf color during the fall season.

A (Chlorophyll in the leaves beginning to break down then) CORRECT

This is the correct answer because the breakdown of chlorophyll directly leads to the unmasking of other pigments such as carotenoids and anthocyanins, which contribute to the yellow and red hues of autumn leaves. Without the degradation of chlorophyll, these colors would not become visible.

B (Heat and light causing new pigments to be produced) YOUR ANSWER

While heat and light do affect leaf color, they do not directly cause the production of new pigments during the fall. Instead, the existing pigments become more prominent due to the breakdown of chlorophyll, rather than the creation of new pigments in this context.

C (Existing pigments becoming more uniform) YOUR ANSWER

This choice implies a homogenization of pigment colors, which does not accurately describe the phenomenon observed in fall foliage. In fact, the colors become more varied and pronounced as chlorophyll degrades, rather than uniform, as different pigments are revealed.

D (New chlorophyll no longer being produced) YOUR ANSWER

The cessation of chlorophyll production is indeed a factor, but it is not the immediate cause of color change. The breakdown of existing chlorophyll is what allows the other pigments to be seen, making this option less direct in explaining the change in leaf color.

Conclusion

The change in leaf color during fall is primarily due to the breakdown of chlorophyll, which exposes other pigments that were previously overshadowed. While various factors influence this process, it is the degradation of chlorophyll that most directly accounts for the vibrant colors of autumn leaves, highlighting the interplay of plant biology with seasonal changes.

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