Question

Plants respond to various stimuli by

A) Shedding leaves

B) Growing

C) Falling of fruits

D) Peeling of bark 

Answer 1

Hint: Plant responds to three main stimuli: water, gravity, and light. Response or orientation of plant shoot and roots towards these stimuli is known as ‘Tropism’. The response to stimuli usually involves the structural alteration in plants.

Complete answer:

Plants respond to various stimuli by growing either towards or away from the stimulus. The different type of tropism seen in plants are:

1. Geotropism: is the response to gravity (stimulus), where shoots grow in the opposite direction to gravity (negative geotropism), and roots grow in the direction of gravity (positive geotropism).

2. Phototropism: light is important to plants for photosynthesis, and so they respond to light (stimulus) by growing shoot in the direction of the light source (positive phototropism) and growing roots away from the light source (negative phototropism).

3. Hydrotropism: water plays an important role in the growth and survival of plants and so the plant responds to the source of water (usually the groundwater) by growing roots deep inside the soil towards the water source. The plant can even grow against gravity if the water source is in an upward direction . Hydrotropism in plants is dominant over geotropism.

4. Haptotropism: it is a response to touch (stimulus), usually seen in climber plants that need support for its growth.

5. Chemotropism: Plant response to chemicals (stimulus) by growing towards the chemicals. For example, the growth of the pollen tube down the style in response to sugar as a chemical stimulus present in style.

Additional Information
Auxins are the plant hormones involved in Tropism. Though the involvement of auxin in hydrotropism is not well studied, its distribution at the tips of the plant structure helps the plant to respond to the light and gravity stimuli. A shoot grows at the tip with a high concentration of auxin and a root grows at the tip with a low concentration of auxins.

So, the correct answer is option B growing.

Note:
While growth is a response of plants towards stimuli, shedding of leaves, falling of fruits, and peeling of bark is a part of the process known as ‘Abscission’. Abscission takes place when auxin gets exhausted in a region of plants, which makes the region more sensitive to ethylene which causes falling of leaves, wilting of flowers, and fruit ripening. Abscission is a mechanism of plants to cut off the unwanted part of the plant to save its resources.