Plant Biology: Roots, Shoots, Stems, and Leaves
Your basic vascular plant parts are roots, shoots, stems, and leaves. Of course, there's a wealth of variety within these types or parts, but it boils down to those four. Each part has distinct functions. Together, these parts reflect how vascular plants evolved to inhabit two distinct environments at the same time: the soil and the air. Why would plants do such a thing? The soil offers water and vital minerals. The air offers carbon dioxide and the energy of sunlight. To forge the successful lifestyles they enjoy today, plants evolved systems to tap into all these resources, both above and below the ground. In short, plants evolved roots and shoots. Shoots, in turn, can develop stems and leaves.
Roots are branched, underground structures that serve two major functions. First, somewhat obviously, roots firmly anchor the plant to a fixed spot. Once a plant takes root and begins to grow in an area with good access to moisture, soil nutrients, and light, it pays to stay. Second, roots serve as transport systems, allowing the plant to suck up water and dissolved nutrients from the soil to support the plant's growth. Roots have specialized parts that develop from the three major types of plant tissue: ground, dermal, and vascular.
Shoots target the above-ground business of the plant. Very young plants may possess only simple, undeveloped shoots. As a plant grows, however, these tender shoots develop into stems and leaves. So, stems and leaves are really part of the shoot system. Stems and leaves are so different and specialized that it is worth considering them separately. Overall, the shoot system enables a plant to grow taller to gain access to energy-giving light, and allows the plant to convert that light energy into the chemical energy of sugar. Like roots, shoots develop from ground, dermal, and vascular tissues.
Stems are sturdy structures that grow in order to give a plant a fighting chance to spread its leaves in the sun. Stem growth can add to the plant's height, broaden the area covered by the leaves, or even direct growth from a dark area toward one with more light. To provide mechanical support for a growing plant, stems need to be strong. To help move water and nutrients to the furthest reaches of the plant, stems are stuffed with little transport pipes in the form of xylem and phloem.
Leaves are the original solar panels, capturing energy from sunlight in a biochemical process called photosynthesis. The cells within leaf tissues are hectic with biochemistry, importing water and nutrients to support their frantic work, and exporting sugar to provide energy to the remainder of the plant. The import/export business conducted by the leaves is supported by xylem and phloem pipelines, which explains why leaves are so richly veined.