Gravitropism facts for kids
Gravitropism (say: grav-ih-TROH-piz-um) is how plants, fungi, and even some animals grow or move in response to gravity. It's also called Geotropism (say: jee-oh-TROH-piz-um). This special kind of growth helps plants know which way is up and which way is down. Most plants, from tiny sprouts to huge trees, use gravitropism.
The famous scientist Charles Darwin was one of the first people to notice this. He observed that plant roots always grow downwards, towards the pull of gravity. At the same time, plant stems and shoots grow upwards, away from gravity. This amazing ability helps plants find water and sunlight.
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How Plants Sense Gravity
Plants have special cells that help them sense gravity. These cells contain tiny, heavy structures called statoliths (say: STAT-oh-liths). Statoliths are like tiny rocks inside the plant cells. They settle at the bottom of the cells due to gravity.
When a plant changes its position, the statoliths shift. This movement tells the plant which way is down. It's like a tiny internal compass that guides the plant's growth.
Roots Grow Down (Positive Gravitropism)
Roots show positive gravitropism. This means they grow towards the pull of gravity. This is very important for plants. Growing downwards helps roots find water and nutrients deep in the soil. It also helps to anchor the plant firmly in the ground.
When a root senses gravity, a plant hormone called auxin (say: AWK-sin) plays a big role. Auxin moves to the lower side of the root. In roots, a high amount of auxin actually slows down cell growth. So, the cells on the top side of the root grow faster than the cells on the bottom. This difference in growth makes the root bend downwards.
Stems Grow Up (Negative Gravitropism)
Stems and shoots show negative gravitropism. This means they grow away from the pull of gravity, towards the sky. This upward growth helps the plant's leaves reach sunlight. Sunlight is essential for photosynthesis, which is how plants make their food.
In stems, auxin works differently than in roots. When a stem senses gravity, auxin also moves to the lower side. But in stems, a higher amount of auxin actually makes cells grow faster. So, the cells on the bottom side of the stem grow faster than the cells on the top. This causes the stem to bend upwards, reaching for the light.
Gravitropism in Action
You can see gravitropism all around you.
- If a potted plant falls over, you'll notice its stem slowly starts to bend upwards again.
- Tree trunks that have fallen often show new branches growing straight up from the fallen trunk.
- Even some fruits, like bananas, show gravitropism. They might curve upwards as they grow on the plant.
Gravitropism is a vital process for plants. It helps them grow in the right direction to survive and thrive in their environment.
Images for kids
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Example of gravitropism in a tree from central Minnesota. This tree has fallen over and due to gravitropism exhibits this arched growth.
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A straight and vertical tree. The shape has been regulated by the gravitropic curvature at the base.
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In the process of plant roots growing in the direction of gravity by gravitropism, high concentrations of auxin move towards the cells on the bottom side of the root. This suppresses growth on this side, while allowing cell elongation on the top of the root. As a consequence of this, curved growth occurs and the root is directed downwards.
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In the process of plant shoots growing opposite the direction of gravity by gravitropism, high concentration of auxin moves towards the bottom side of the shoot to initiate cell growth of the bottom cells, while suppressing cell growth on the top of the shoot. This allows the bottom cells of the shoot to continue a curved growth and elongate its cells upward, away from the pull of gravity as the auxin move towards the bottom of the shoot.
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Banana fruit exhibiting negative geotropism.
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The compensation reaction of the bending Coprinus stem. C – the compensating part of the stem.
See also
In Spanish: Gravitropismo para niños
