The root

The root begins as the radicle

A seed holds a tiny plant, the embryo. One end of the embryo is a small root-to-be, the radicle. When the seed sprouts, the radicle pushes down into the soil and grows into the root of the plant.

A root does four jobs.

• It absorbs water and minerals from the soil.
• It anchors the plant in the ground.
• It may store reserve food.
• It makes some plant growth regulators, the chemicals that control how a plant grows.

Three kinds of root

• Tap root system. The primary root grows straight from the radicle and keeps growing. It puts out lateral roots, which branch again. Mustard, gram and mango have this system, and so do most dicots.
• Fibrous root system. In a monocot, the primary root lives only a short time. A crowd of thin roots of about the same size takes its place. They grow from the base of the stem. Wheat and grass have fibrous roots.
• Adventitious roots. These roots grow from parts of the plant other than the radicle. Grass, Monstera and the banyan tree have them.

The tip of a young root

Look closely at the tip of a young root. You can find four regions, from the tip upwards.

• The root cap is a thimble-like cover over the tip. It protects the tender tip as the root pushes through the soil.
• The region of meristematic activity lies just above the cap. Its cells are small and thin-walled, with dense protoplasm. They divide again and again, so this region makes new cells.
• The region of elongation comes next. Its cells lengthen and grow larger. This region makes the root longer.
• The region of maturation is the oldest part. Its cells change into the mature kinds of cell. Some cells of the outer layer grow into very fine, thread-like root hairs. Root hairs absorb water and minerals from the soil.

Slide the arrow along the root. The region changes at each boundary. Root hairs appear only in the region of maturation.

Try it in Python

The program lists six plants with their root system, and counts how many plants have each system.

Practise with new numbers

Roots with other jobs

A root can change its shape to do a special job.

• Storing food. The tap roots of carrot, turnip and radish are swollen with stored food. The adventitious roots of sweet potato store food too.
• Support. The prop roots of the banyan tree hang down from its branches and hold up the heavy tree, like pillars. The stilt roots of maize and sugarcane grow from the lower nodes of the stem and brace it.
• Breathing. Marshy ground has little air. Mangrove trees such as Rhizophora grow pneumatophores, roots that grow upwards out of the mud. They have pores through which the roots take in oxygen.

Common mistakes

• Thinking the root cap makes the root grow. The cap only protects the tip. The region of meristematic activity makes the new cells.
• Placing root hairs in the cap or in the region of elongation. They belong to the region of maturation.
• Mixing up prop roots and stilt roots. Prop roots hang from branches. Stilt roots grow from the lower nodes of the stem.
• Calling every swollen underground part a root. Potato and ginger are stems, as the next lesson shows.

Remember these

• Tap root system: primary root from the radicle, with lateral roots (dicots). Fibrous root system: many thin roots from the base of the stem (monocots).
• Adventitious roots grow from parts other than the radicle.
• Root tip, from the tip upwards: root cap, meristematic region, region of elongation, region of maturation with root hairs.
• Storage: carrot, turnip, radish, sweet potato. Support: prop roots of banyan, stilt roots of maize and sugarcane. Breathing: pneumatophores of Rhizophora.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Which root system has a primary root that grows from the radicle and stays?

2. Name the region of a root tip that makes the root longer.

3. Where are root hairs found, and what do they do?

4. What job do the pneumatophores of a mangrove tree do?

5. Name one root that stores food.