Defining Phototropism
Phototropism is the directional growth of a plant in response to a light source. The term comes from the Greek words 'photo' (light) and 'tropos' (turning). It is a crucial survival mechanism that allows plants to orient their stems and leaves towards the sun to maximize light absorption for photosynthesis.
Section 2: The Mechanism Behind the Movement
The process is primarily regulated by a plant hormone called auxin. Auxin is produced at the tip of the stem and is sensitive to light. When light shines on one side of the stem, auxin migrates to and accumulates on the shaded side. This higher concentration of auxin stimulates cell elongation on the dark side, causing the stem to bend and grow towards the light.
Section 3: A Practical Example
A common example of phototropism can be seen with a houseplant placed on a windowsill. Over time, you will notice the plant's stem and leaves bending towards the window. This is the plant actively adjusting its position to capture the maximum amount of available sunlight for energy production.
Section 4: Positive vs. Negative Phototropism
Plant stems and leaves exhibit positive phototropism, meaning they grow towards light. In contrast, plant roots often exhibit negative phototropism, growing away from light and deeper into the soil. This ensures the roots anchor the plant securely and find essential water and nutrients underground.