NEET 2023 Botany Ethylene MCQ Question

Explanation:

The question asks which hormone promotes internode and petiole elongation in deep water rice. The correct answer according to the instructions is B) Ethylene, though the initial indication was that D) GA3 (Gibberellin A3) was correct. Let's clarify this.

Correct Answer: Ethylene (B)

Why Ethylene is Correct:

• Ethylene is a plant hormone known for its role in promoting growth in response to environmental stimuli. In deep water rice, where water levels can rise significantly, the plants must elongate their internodes and petioles to keep their leaves above water. Ethylene is produced in response to submergence and is crucial for this adaptive response.
• Ethylene stimulates elongation by promoting cell expansion and division, particularly in the areas of the plant that are submerged, allowing the plant to grow taller quickly.

Why Other Options are Incorrect:

A) Kinetin:

• Kinetin is a type of cytokinin, which primarily promotes cell division and shoot formation. While it can influence growth, it does not specifically promote elongation in deep water conditions as effectively as ethylene does.

C) 2, 4-D:

• 2, 4-D is a synthetic auxin that is primarily used as a herbicide. It can promote elongation in certain contexts, but it does not play a significant role in the adaptive elongation of deep water rice. Its primary function is more related to weed control than to promoting growth in submerged conditions.

D) GA3 (Gibberellin A3):

• Gibberellins, including GA3, are known for promoting elongation and growth in various plants, particularly in seed germination and stem elongation in some contexts. However, in the specific case of deep water rice, ethylene is the key hormone that triggers the elongation response due to flooding, rather than gibberellins.

Summary

In summary, while gibberellins play a general role in promoting growth, ethylene is the specific hormone that mediates the critical adaptation of elongation in deep water rice due to its response to submergence. Thus, the correct answer is B) Ethylene.

This highlights the importance of understanding the specific roles of plant hormones in various physiological and environmental contexts. Each hormone has distinct functions, and knowing these can help in predicting plant responses to environmental changes.