OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

Why do leaves change color in autumn?

1. Reduction in soil nutrients

2. Decrease in chlorophyll production

3. Increase in rainfall during autumn

4. Increased temperatures in autumn

The correct answer is: Decrease in chlorophyll production

Leaves change color in autumn primarily due to a decrease in chlorophyll production. During the growing season, chlorophyll, the pigment responsible for the green color in leaves, is abundant as it plays a crucial role in photosynthesis, allowing plants to absorb sunlight and convert it into energy. As daylight hours shorten and temperatures cool in autumn, chlorophyll breaks down and is not replaced. As the chlorophyll fades, other pigments that were present in the leaves all along become more visible. These pigments include carotenoids, which produce yellow and orange hues, and anthocyanins, which can create red and purple shades. This pigment shift illustrates the process of senescence in leaves, preparing trees for winter when they conserve resources by shedding leaves that can no longer efficiently carry out photosynthesis due to limited sunlight and water availability. The other options do not directly contribute to the color change process. Soil nutrient reduction may impact leaf health in general, but it is not a primary factor for color change. Rainfall increases and temperature rises generally occur in spring and summer and do not play a significant role in the autumnal color transformation context.