9 Questions
What is the effect of auxin accumulation on the side of the root facing water during hydrotropism?
It inhibits elongation on that side
In the case of hydrotropism in roots, the accumulation of auxins occurs on which side of the root?
The side facing water
In which of the following cases does tropism occur in the same direction as the accumulation of auxins?
All of the above
Which of the following statements about tropisms and auxin accumulation is NOT true?
In negative phototropism for vertically-positioned roots, tropism occurs in the same direction as auxin accumulation
If a root is placed in a horizontal position, which tropism would cause it to curve downwards?
Positive geotropism
If a stem is placed in a vertical position, which tropism would cause it to curve towards a light source?
Positive phototropism
In which of the following cases does tropism have no effect?
Hydrotropism for stems
If a root is placed in a vertical position and exposed to a light source, which tropism(s) would cause it to curve away from the light source?
Negative phototropism only
Which of the following statements about auxin accumulation and tropisms is correct?
In positive geotropism for roots, auxins accumulate on the upper side of the root
Study Notes
Tropism
- Tropism is the curvature of a plant's stem or root in response to external stimuli such as light, humidity, and gravity.
- There are three types of tropism: phototropism, geotropism, and hydrotropism.
Phototropism
- Phototropism is the response of plant parts to light, causing curvature towards or away from the light.
- Stem is positive phototropic, meaning it grows towards the light.
- Root is negative phototropic, meaning it grows away from the light.
- Experiment: placing a seedling on a cork disc in a light-proof box with a small hole to admit light, and observing the stem's curvature towards the light and the root's curvature away from the light.
- Auxins play a crucial role in phototropism, with higher concentration of auxins on the side of the stem away from light, leading to faster growth and curvature towards the light.
- Lower concentration of auxins on the side of the root near light, leading to slower growth and curvature away from light.
Geotropism
- Geotropism is the response of plant parts to gravity, causing movement towards or away from the stimulus.
- Stem is negative geotropic, meaning it grows away from gravity.
- Root is positive geotropic, meaning it grows towards gravity.
- Experiment: germinating seeds in a soil and observing the stem's growth upwards and the root's growth downwards.
- Auxins accumulate in the lower side of both the root and the stem when the plant grows in a horizontal position, leading to negative geotropism in the stem and positive geotropism in the root.
Hydrotropism
- Hydrotropism is the response of plant parts to humidity, causing movement towards or away from the stimulus.
- Root is positive hydrotropic, meaning it grows towards water.
- Experiment: germinating seeds in two glass troughs with different water distributions, and observing the root's curvature towards the water at the sides.
- Auxins accumulate in the side of the root facing water, inhibiting cell elongation and leading to curvature towards the water.
Test your knowledge on plant tropism, the phenomenon where plants grow or move in response to different external factors such as light, gravity, and humidity. Learn about different types of tropism like phototropism, geotropism, and hydrotropism.
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