DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Roots of a plant of annual sunflower, Helianthus annuus. Annual plants gain nutrients and water from the soil by means of a network of primary roots. Roots grow downwards due to geotropism; the ability to sense gravity, located at the root tip. As each root grows, it produces a zone of fine hairs ( root hairs ) behind the tip, that greatly increases the surface area in contact with the soil. Further behind the tip, side roots ( lateral roots ) are produced, and these in turn produce more root hairs as they extend. The picture shows primary roots growing from the base of the plant. The youngest parts are bright white, and root hairs are visible in these regions of the root system.
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