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How Do Plants Grow Towards Light?


How Do Plants Grow Towards Light?
Plants depend on a process called photosynthesis to make their own food. This process converts water from the soil and carbon dioxide in the air into oxygen and glucose (sugar). Sunlight is crucial for this chemical change and without it, green plants are unable to survive.

Plant cells contain a protein called phototropin, which is activated when it absorbs the blue wavelength of light. This leads to an uneven distribution of the hormone auxin (which regulates growth) in the stem. The exact mechanisms behind this process are not fully understood, but one theory is that sunlight destroys or inhibits auxin so the hormone levels on the Sun-facing side reduce. Another theory is that auxin molecules are able to move from cell to cell across the stem, away from the area where light was detected by the phototropins. Auxin causes cells to enlarge, so the shaded side of the stem – which contains higher levels of the hormone – elongates, forcing the plant to bend towards the light as a result.
How Do Plants Grow Towards Light?

Sunflowers take their quest for sunlight to the extreme. These plants follow the Sun throughout the day, physically rotating their leaves and flowers to make the most of the available light. At night they then unwind, returning to their starting position ready for sunrise. No one knows why the flowers follow the Sun as well as the leaves, although it’s thought the extra heat may help to grow more seeds.