Science (086) — AI-generated practice question

The bending of the shoot is a tropic movement caused by growth. When light falls from one side, auxin diffuses to the shady side of the shoot tip, causing cells there to elongate more. This unequal growth permanently bends the shoot toward light.

Once cells have already grown and elongated, they cannot shrink back — growth is irreversible. The old, bent cells have permanently increased in length. Only the new cells forming at the growing tip will respond to the changed direction of light and grow in the new direction. Therefore, only new growth reorients; the old bent portion stays curved.

Source: Chapter 6, Section 6.2.2 — Movement Due to Growth

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• The key concept examiners want: tropic (phototropic) movements are growth-based and therefore irreversible — once cells elongate, they don't shrink.
• Mention auxin and unequal cell elongation for full marks.
• The textbook Activity 6.2 explicitly asks students to observe that "old parts do not change direction" — this is a direct exam point.
• A common mistake is saying the plant "forgets" the light direction; the correct reason is biological: cell elongation is a one-way process.