Question

The shoot system of any plant responds towards the stimulus of
A. Air
B. Light
C. Water
D. Soil

Answer 1

Hint: The shoot or stem of the plant grows above the soil.
The growth is against gravity and soil, though it needs water to live it does not grow towards the soil. Stems only grow when sunlight falls on it.

Complete answer: The shoot of a plant comprises the stems, leaves, flowers, and fruits. In some plants, adventitious roots are also seen in stems.
Light is one of the most important stimuli that is responsible for stem growth.
This is called phototropism. It involves growth toward or away from a light source.
Photo means light and tropism means movement.
The mechanism is as follows:
1. In the shoot, a hormone named auxin is produced at the tip of the shoot.
2. It diffused from the tip and moved down the shoot.
3. If a light source is present from one side on the tip side of the stem, the auxin moves to the opposite side that is away from light – means the shaded side.
4. In the shade’s side of the shoot, the cells grow more due to the presence of auxin.
This results in the bending of shot towards the light. This phenomenon is also called positive phototropism.
5. When movement is seen away from light – it is called negative phototropism. This is seen in roots.

So, the correct answer is option is B. Light.

Note: Plant movement is seen in response to other two stimuli:
1. Water – Roots grow towards water (positive hydrotropism) and stems grow away from water (negative hydrotropism).
2. Gravity - Roots grow towards gravitation force (positive geotropism) and stems grow away from gravitation force (negative geotropism).