A root is an organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates. Most vascular plants have two types of roots: primary roots that grow downward and secondary roots that branch out to the side. Together, all the roots of a plant make up a root system.
There are two basic types of root systems in plants: taproot systems and fibrous root systems.
- Taproot system
Taproot systems feature a single, thick primary root, called the taproot, with smaller secondary roots growing out from the sides. When a seed germinates, the first root to emerge is the radicle, or primary root. The taproot may penetrate as many as 60 meters (almost 200 feet) below the ground surface. It can plumb very deep water sources and store a lot of food to help the plant survive drought and other environmental extremes. Taproots modified for use in storage (usually carbohydrates) are found in sugar beet or carrot. The taproot also anchors the plant very securely in the ground.
- Fibrous root system
Fibrous root systems have many small branching roots, called fibrous roots, but no large primary root. In this case the radicle from a germinating seed is short lived and is replaced by adventitious roots. Adventitious roots are roots that form on plant organs other than roots.The huge number of threadlike roots increases the surface area for absorption of water and minerals, but fibrous roots anchor the plant less securely. Most monocots have fibrous root systems. Some fibrous roots are used as storage; for example sweet potatoes form on fibrous roots.
Root Structures and Functions
The tip of a root is called the root cap. It consists of specialized cells that help regulate primary growth of the root at the tip. Above the root cap is primary meristem, where growth in length occurs.
Above the meristem, the rest of the root is covered with a single layer of epidermal cells. These cells may have root hairs that increase the surface area for the absorption of water and minerals from the soil. Beneath the epidermis is ground tissue, which may be filled with stored starch. Bundles of vascular tissues form the center of the root and is called stele. Waxy layers waterproof the vascular tissues so they don’t leak, making them more efficient at carrying fluids. Secondary meristem is located within and around the vascular tissues. This is where growth in thickness occurs.
The structure of roots helps them perform their primary functions and the three main duties are: absorbing water and minerals, anchoring and supporting the plant and storing food.
- Absorbing water and minerals
Thin-walled epidermal cells and root hairs are well suited to absorb water and dissolved minerals from the soil. The roots of many plants also have a mycorrhizal relationship with fungi for greater absorption.
- Anchoring and supporting the plant
Root systems help anchor plants to the ground, allowing plants to grow tall without toppling over. A tough covering may replace the epidermis in older roots, making them rope like and even stronger. Some roots may have unusual specializations for anchoring plants.
- Storing food
In many plants, ground tissues in roots store food produced by the leaves during photosynthesis. One such is the blood root that stores the food in its roots over the winter.
The root system of a plant constantly provides the stems and leaves with water and dissolved minerals. In order to accomplish this the roots must grow into new regions of the soil. The growth and metabolism of the plant root system is supported by the process of photosynthesis occurring in the leaves. Photosynthate from the leaves is transported via the phloem to the root system. Root structure aids in this process.