Plants and Water
Most plants grow in the ground, with stems above, and roots below. Water and some nutrients come from the roots. The evaporation of water from pores in the leaves pulls water through the plant. This is called transpiration.
A plant needs sunlight, carbon dioxide, minerals and water to make food. A green substance in plants called chlorophyll traps the energy from the Sun needed to make food. Chlorophyll is mostly found in leaves, inside plastids, which are inside the leaf cells. The leaf can be thought of as a food factory. Leaves of plants vary in shape and size, but they are always the plant organ best suited to capture solar energy. Once the food is made in the leaf, it is transported to the other parts of the plant such as stems and roots.
The roots of plants perform two main functions. First, they anchor the plant to the ground. Second, they absorb water and various nutrients dissolved in water from the soil. Plants use the water to make food. The water also provides the plant with support. Plants that lack water become very limp and their stems cannot support their leaves. Water is transported from the roots to the rest of the plant through special vessels in the plant. When the water reaches the leaves, some of it evaporates into the air. Many plants need the help of fungi to make their roots work properly. This plant/fungi symbiosis is called mycorrhiza. Rhizobia bacteria in root nodules help some plants get nitrogen.
See also: http://en.wikipedia.org/wiki/Plant_nutrition
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)