Fall color occurs because:

• A. Breakdown of green chlorophyll in the leaves and the expression of other pigments that are always present
• B. Increase in chlorophyll production
• C. Loss of all pigments
• D. Excess water in leaves

Answer: (A)

Fall color comes from the breakdown of the green chlorophyll in leaves as days shorten and temperatures cool. As chlorophyll fades, pigments that are always in the leaf but masked by the chlorophyll—carotenoids (yellow/orange) and, in some trees, anthocyanins (red/purple)—become visible, producing the autumn hues. The pigments themselves are not newly produced in autumn; carotenoids are constant components, only revealed when chlorophyll declines.

The other ideas don’t fit: increasing chlorophyll production would keep leaves green rather than show colors; losing all pigments would produce a washed-out look rather than the range of fall colors observed; excess water in leaves isn’t what drives the color change.