Question

Sunflower seedling, growing in moist soil in a flower pot, was placed inside a cardboard box with a lid. A window was cut in one side of the box to admit light on the right-hand side of the seedlings. The drawing shows the shoot of one of the seedlings at the start of the experiment.
(i) What name is given to the response made by the seedling?
(ii) What was the stimulus which produced this response?
(iii) What control experiment could be set up to check that the response was made to the stimulus suggested in (b)?

• A. (i)- Phototropism; (ii)- Sunlight; (iii)- Plant can be kept in a dark chamber
• B. (i)- Geotropism; (ii)- Sunlight; (iii)- Plant can be kept under tube light
• C. (i)- Phototropism; (ii)- Water; (iii)- Plant can be kept under the light
• D. (i)- Geotropism; (ii)- Gravity; (iii)- Plant can be kept in a dark chamber

Answer 1

The correct option is A (i)- Phototropism; (ii)- Sunlight; (iii)- Plant can be kept in a dark chamber

Geotropism (also known as gravitropism) is a turning or growth movement by a plant or fungus in response to gravity. It is a general feature of all higher and many lower plants as well as other organisms. Phototropism is the growth of organisms in response to a light stimulus. It is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth.

Hence, the correct answer is option A.