NDA (II) 2021 General Ability Test · Question 107 of 149

Correct — D, Negatively geotropic. Geotropism (also called gravitropism) is a plant's directional growth in response to gravity. A shoot grows upward, that is, away from the pull of gravity, so it shows negative geotropism. Roots, which grow downward toward gravity, are positively geotropic. Since the movement here is defined relative to gravity and is directed away from it, the shoot is negatively geotropic.

• (a)Negatively phototropic — Phototropism is a response to light, and shoots actually bend toward light, so they are positively phototropic, not negatively. The upward movement described here is defined against gravity, not light.
• (b)Positively chemotropic — Chemotropism is growth toward a chemical, as in a pollen tube growing toward chemicals in the ovule; it does not describe a shoot rising against gravity.
• (c)Positively hydrotropic — Hydrotropism is growth toward water, shown mainly by roots; it does not explain the upward growth of a shoot.

Tropisms are directional growth movements of plants in response to a stimulus. Each is named after its stimulus: light gives phototropism, gravity gives geotropism, water gives hydrotropism and chemicals give chemotropism. The response is positive if growth is toward the stimulus and negative if away from it.

The key is to spot which stimulus the question defines the movement against. Upward movement is described relative to gravity, so the relevant tropism is geotropism, and because the shoot grows away from gravity it is negative. The same shoot is also positively phototropic, but that is not the option offered.

• Geotropism (gravitropism) is directional growth in response to gravity.
• Shoots grow away from gravity, so they are negatively geotropic; roots grow toward gravity and are positively geotropic.
• Positive means toward the stimulus and negative means away from it.
• Other tropisms include phototropism (light), hydrotropism (water) and chemotropism (chemicals).

• Reading 'upward' as a light response (phototropism) when the option names the response against gravity (geotropism).
• Mixing up positive and negative: a shoot moves away from gravity, so it is negatively geotropic.

Asked as the tropism shown by an upward-growing shoot; match the stimulus (gravity, hence geotropism) and the direction (away, hence negative).

No directly related past PYQ was found.

• practice — not a real PYQ

  The downward growth of a plant root toward gravity is an example of

  • (a)Positive phototropism
  • (b)Positive geotropism
  • (c)Negative geotropism
  • (d)Positive hydrotropism

  Answer(b) Positive geotropism — the root grows toward the pull of gravity.

• practice — not a real PYQ

  The bending of a plant shoot toward a source of light is called

  • (a)Positive phototropism
  • (b)Negative phototropism
  • (c)Geotropism
  • (d)Chemotropism

  Answer(a) Positive phototropism — the shoot grows toward the light.