Q1. [3] medium thorough-understanding
The roots of a germinating seed always grow downward into the soil, while the shoot grows upward. Name the stimulus responsible for this directional growth. For each organ (root and shoot), state whether its response is positive or negative with respect to that stimulus, and explain the advantage of this arrangement for the seedling.
Generated by claude-sonnet-4-6 · 2026-06-26 01:02 · grounding rag
Model Answer
Stimulus: Gravity (the pull of the earth). The directional growth in response to gravity is called geotropism.
- Root: Shows positive geotropism — it grows downward, towards the pull of gravity.
- Shoot: Shows negative geotropism — it grows upward, away from the pull of gravity.
Advantage: This arrangement ensures the root grows into the soil to absorb water and minerals, while the shoot grows upward towards sunlight for photosynthesis. Together, this helps the seedling survive and establish itself.
Source: Chapter 6, Section 6.2.2 — Movement Due to Growth
---
Explanation
- The key term examiners expect is geotropism (not just "gravity response").
- Always pair the organ with the correct positive/negative label — this is where most marks are awarded.
- The advantage part is often missed; write one line each for root and shoot to be safe.
- Do not confuse geotropism with phototropism (response to light); here the stimulus is specifically gravity.