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Select the INCORRECT statement related to tropism.
Chemotropism – movement towards chemical
Phototropism – movement towards water
Hydrotropism – movement towards water
Geotropism – in response to the pull of earth or gravity
Phototropism – movement towards water
Tropism is the growth or movement of a plant in response to an external stimulus. 'Phototropism' refers to the movement or growth of a plant in response to light, whereas 'Hydrotropism' is the response specifically towards water.
Tropism is the growth or movement of a plant in response to an external stimulus. 'Phototropism' refers to the movement or growth of a plant in response to light, whereas 'Hydrotropism' is the response specifically towards water.
Think of a sunflower 'chasing' the sun across the sky during the day, which is a classic demonstration of phototropism, compared to roots reaching deep into the soil to find a hidden water source.
Remember the prefixes: Photo (Light), Geo (Gravity/Earth), Hydro (Water), Chemo (Chemical).
Plants respond to environmental stimuli through the differential distribution of plant hormones called auxins. In phototropism, auxin accumulates on the shaded side of the shoot, stimulating cell elongation on that side and causing the plant to bend towards the light source. Conversely, hydrotropism involves root growth patterns influenced by moisture gradients in the soil.
Phototropism: Growth response towards a light stimulus.
Hydrotropism: Growth response towards a water stimulus.
Geotropism: Growth response towards or away from gravity (gravitropism).
Chemotropism: Growth response towards or away from a chemical gradient.
Roots growing downwards (positive geotropism)
Pollen tubes growing towards the ovule (positive chemotropism)
Phototropism is controlled primarily by the light-sensitive protein phototropin and the redistribution of indole-3-acetic acid (auxin).
Option B is the incorrect statement because phototropism is the movement in response to light, not water.
B is correct — Phototropism describes movement in response to light, while movement towards water is defined as Hydrotropism.
When answering biology questions about plant movements, always match the Greek root prefix (Photo-, Hydro-, Geo-, Chemo-) directly to the environmental stimulus to avoid confusion.
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