Charles and Francis Darwin discovered that
a. Auxin is responsible for phototropic curvature
b. Red light is most effective in shoot phototropism
c. Light destroys auxin
d. Light is perceived by the tips of coleoptiles

Verified step by step guidance

1. Understand the context: Charles and Francis Darwin conducted experiments on plant growth, particularly focusing on how plants respond to light, a phenomenon known as phototropism.
2. Identify the key terms: Phototropism is the growth of a plant in response to light direction. Coleoptiles are protective sheaths covering the emerging shoot in monocotyledons like grasses.
3. Review the historical experiment: The Darwins observed that when the tips of coleoptiles were covered, the plants did not bend towards the light, suggesting that the light perception occurs at the tip.
4. Analyze the options: a) Auxin's role in phototropism was discovered later by other scientists. b) Red light is more related to photoperiodism, not phototropism. c) Light does not destroy auxin; it influences its distribution. d) The Darwins' experiment showed that light is perceived by the tips of coleoptiles.
5. Conclude based on evidence: The correct conclusion from the Darwins' experiment is that light is perceived by the tips of coleoptiles, which is option d.

Key Concepts

Phototropism

Phototropism is the growth response of a plant in direction to light. It is a crucial adaptive mechanism that allows plants to maximize light absorption for photosynthesis. The process involves the differential growth of plant cells, often mediated by the plant hormone auxin, which redistributes in response to light, causing the plant to bend towards the light source.

Auxin

Auxin is a class of plant hormones that play a key role in coordinating various growth and behavioral processes in the plant's life cycle. It is primarily involved in cell elongation, root formation, and response to light and gravity. In phototropism, auxin distribution is altered by light, leading to differential growth and bending of the plant towards the light source.

Coleoptiles

Coleoptiles are protective sheaths covering the emerging shoot in monocotyledons, such as grasses. They play a significant role in phototropism by perceiving light at their tips, which then influences the distribution of auxin. This perception and subsequent hormonal signaling are crucial for the directional growth of the plant towards light.