Flashcards · Biology · Plant Hormones
Auxins, Phototropism and Gravitropism
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What is phototropism?
A growth response to light.
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What is gravitropism?
A growth response to gravity, also called geotropism.
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Where is auxin made?
In the tips of shoots and roots.
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What does auxin do in a shoot?
Makes the cells elongate.
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What causes a shoot to bend towards light?
More auxin on the shaded side, so the shaded side grows faster.
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What does unequal distribution of auxin cause?
Unequal growth rates in roots and shoots.
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Where does auxin collect in a seedling on its side?
On the lower side.
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Why does the shoot bend upwards?
The lower side grows faster.
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Why does the root bend downwards?
Auxin slows growth on the lower side, so the upper side grows faster.
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What type of phototropism does a shoot show?
Positive, as it grows towards light.
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What type of gravitropism does a shoot show?
Negative, as it grows away from gravity.
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What type of gravitropism does a root show?
Positive, as it grows towards gravity.
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Why is phototropism useful?
It puts the leaves in the best position for photosynthesis.
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Why is gravitropism useful in a root?
It grows down to find water and mineral ions and anchor the plant.
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Why do plants respond more slowly than animals?
Hormones travel slowly, and growth takes time.
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Common mistake about auxin?
Saying it moves to the lit side. It moves to the shaded side.