Question

Plants bend toward the light because

• A. They need light for photosynthesis
• B. They need light for respiration
• C. Light attracts them
• D. Cells on the shaded side elongate more

Answer 1

The correct option is D Cells on the shaded side elongate more

Light is an important factor influencing plant growth. It is a common observation that plants grow towards light. Charles Darwin and his son Francis Darwin first observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism). After a series of experiments, it was concluded that the tip of coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile due to more growth on the dark side. That transmittable influence is now thought to be the phytohormone auxin.

So, the correct answer is 'Cells on the shaded side elongate more'