A seed produces a root before anything else for two reasons. The root holds the rest of the plant in the soil. If a plant did not have a root it would easily blow away. The second reason the seed produces the root first is equally vital. The root takes in water and minerals from the soil. But to do this the root needs a very large surface to soak up the water, and this is created by tiny root hairs. Large numbers of root hairs grow just behind the root tip. As the root grows through the soil the hairs become more distant from the root tip and die. They are replaced by new hairs that are always growing from just behind the tip.

As the root grows, it sends out branches called side roots. Like the main root, they have protective caps and root hairs. In many plants the first root grows larger than the others. It is longer and thicker than the other roots and is called a tap root. Plants such as the carrot produce a tap root to store food over winter. It uses this food to make leaves and flowers in the following year. Desert plants such as the creosote bush produce tap roots to store water. This is used to keep the plant alive through the long periods of dry weather. In some plants there is not a clear main root. These plants, such as the grass, produce many long thin roots called fibrous roots. These kind of roots can also grow out from the sides of a tap root.

A root does not have to use any energy to take in water from the soil. The water seeps into the root hairs naturally (its a process scientists call osmosis, but you don't have to remember that). There are tiny pipes in the centre of a root and the water collects there. As the amount of water increases it flows along the pipes and pushes a little way up the pipes in the stem. If the stem of a small sunflower seedling is cut a large drop of water may form on the top of the cut end due to the root pushing up the water.

The water in the soil contains minerals that the plant needs. The roots use energy from food in order to grow. The roots get oxygen from air in spaces in the soil and combine this with their food to make energy and new root. So, if the soil is drenched and full of water, the water drives out the air and the roots cannot get the oxygen they need. This is why too much water in the soil can stop the root working properly and kill the plant. Many house plants are killed by people over-watering the soil in the pots.