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

What characterizes the growth pattern of shoots in response to light?

1. The growth occurs only during the day

2. The growth direction changes based on light intensity

3. The growth remains constant regardless of light

4. The growth is enhanced in complete darkness

The correct answer is: The growth direction changes based on light intensity

The growth pattern of shoots in response to light is primarily characterized by phototropism, which is the directional growth of a plant towards light. This means that shoots will grow towards the light source, allowing them to maximize their exposure to sunlight, which is essential for photosynthesis. Phototropic responses occur due to the differential distribution of growth hormones, primarily auxins, which cause cells on the opposite side of the light source to elongate more than those on the side exposed to light. This results in the shoot bending towards the light. The second choice reflects that the direction of growth can indeed change based on the intensity and angle of the light. If light intensity varies, the plant adapts its growth to optimize light capture, effectively changing its growth direction. Thus, phototropism is a crucial adaptation that enhances a plant's survival by ensuring it can photosynthesize efficiently. The other choices do not accurately reflect how plants respond to light. Growth that occurs only during the day overlooks that many plants continue to grow in the presence of light conditions that vary throughout the day and night. Constant growth regardless of light does not account for the important role that light plays in signaling and metabolic processes in plants. Lastly, while some growth processes continue in darkness, such as cellular