Study Guides/Biology/Phototropism in Plants

Study Guide · Biology

How does Phototropism occur in Plants?

Have you ever noticed that a potted plant kept near a window will slowly bend and grow towards the sunlight? This directional movement of a plant part in response to light is called Phototropism. Let's see exactly how it happens.

Question (Click to Flip)

How does phototropism occur in plants?

Answer

Phototropism occurs when light falls on one side of a plant. The hormone auxin accumulates on the shady side of the stem, causing the cells there to elongate faster. This uneven growth makes the plant bend toward the light.

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Key Facts

Definition: Directional growth of a plant towards light.

Key Hormone: Auxin.

Mechanism: Auxin collects on the shady side, causing those cells to elongate faster, which pushes the plant to bend toward the light.

The Definition

Photo means Light.
Tropism means Directional Movement. Therefore, Phototropism is the directional growth of a plant shoot towards the source of light.

The Mechanism: Role of Auxin

Phototropism occurs due to the action of a plant hormone called Auxin.

Production: Auxin is synthesized at the very tip of the plant shoot.
Uneven Light: When sunlight falls straight down from above, auxin spreads evenly, and the plant grows straight up. However, when sunlight falls on the plant from only one side (like from a window), the auxin hormone reacts.
Diffusion to the Shade: Auxin dislikes light. It diffuses and accumulates on the shady side of the shoot (the side away from the sun).
Uneven Growth: Auxin stimulates cells to grow longer. Because there is more auxin on the shady side, the cells on the shady side grow faster and longer than the cells on the sunny side.
The Bend: This uneven growth causes the stem to bend towards the light.

Questions and Answers

How does phototropism occur in plants?+

Phototropism occurs when light falls on one side of a plant. The hormone auxin accumulates on the shady side of the stem, causing the cells there to elongate faster. This uneven growth makes the plant bend toward the light.

Which hormone is responsible for phototropism?+

The plant hormone responsible for phototropism is Auxin.

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