Ray was a member of Science Olympiad, participates in science and health writing competitions, and studied at a sci-tech school.
What Is a Root?
The root is the part of a plant that attaches it to the ground. It's where water and nourishment begin to be transported to the rest of the plant structure via its branches and fibers. Roots are usually under the ground and function as an organ of absorption, aeration, food storage, and anchorage or support. They are the part of vascular plants that is best defined as the non-leaf, non-stem parts of the plant's body.
The Four Main Functions of Roots
Grasp a weed and try to pull it from the ground. Do the same with several plants. Notice the force you must exert to pull them loose. Roots hold, or "anchor," a plant firmly to the ground. The first root that develops from the seed is the primary root. After some time, secondary roots develop from the primary root. Secondary roots originate from the pericycle of a primary root, and they are made up of many cells.
2. Absorption of Water and Minerals
Water and minerals needed by plants are found in the soil. Root epidermal cells have very thin walls; they can absorb water and dissolve substances with or without root hairs. The root hairs are extensions of epidermal cells near the root tip, and they increase the surface area of an epidermal cell. This makes absorption more efficient. A root hair originates from the epidermis and is not considered a cell; it is only an extension of one epidermal cell.
Some roots come up from the soil or grow from the plant stem or leaf tissues. These are roots that grow on the above-ground parts of a plant, acting as woody vines that anchor to different tree branches, trellises, rocks, and walls. The anchorage of these aerating roots fixes the plant from external environmental factors such as wind. Many aerial roots also intake gases, moisture, or nutrients directly from the air.
4. Food Storage
Roots are a food storage structure for plants. They are good for storing nutrients, starches, and sugars. In tubers, rhizomes, and other starch-storing plant organs, roots also act as a place to store food for later use. In some plants, roots are enlarged to accommodate large quantities of starch and other carbohydrates. Examples of root vegetables are beets, carrots, and sweet potatoes.
How Do Roots Grow So Deep?
Roots can penetrate deep into the soil, no matter how closely packed the soil particles are. What makes roots capable of doing this? They give off carbon dioxide as a result of respiration, and carbon dioxide reacts with water in the soil, forming carbonic acid. Carbonic acid dissolves certain minerals in the soil, making it easier for the roots to penetrate the earth.
The Structure of a Root
The different parts of a root can be defined by the roles they perform in the plant's cellular growth process.
1. Cell Division (the Root's Tip)
The tip of the root is made up of cells that divide often. This is called the region of cell division. The rapidly dividing cells can be described as "meristematic." Meristematic cells are usually small since they are newly formed. These delicate cells at the root tip are protected from mechanical injury by a mass of cells called the root cap. The cells of the root cap are worn away by contact with soil particles. The destroyed cells are replaced by new cells formed at the very tip of the root, some of which become part of the cap while some become part of the root itself.
2. Cell Elongation
Just above the region of cell division is the region of cell elongation. This is where the cells grow to the normal size of root cells. As young cells grow to normal size, more cells are formed at the root tip.
The cells in this region increase in volume faster than the increase in the amount of cytoplasm inside. As a result, more and more vacuoles are formed. The small vacuoles eventually fuse and form a large central vacuole that becomes full of water from the soil. An increase in length results from two factors:
- Increase in the number of cells in the region of cell division
- Elongation of the new cells in the region of cell elongation
These two regions together are very short, often only about 2 millimeters.
3. Cell Maturation (Root Hair Zone)
Just above the region of cell elongation is where the cells mature—they differentiate, becoming specialized to perform specific functions. For instance, some cells become xylem cells, some become phloem cells, and some become cortical (cortex) cells.
The epidermal cells in this region have root hairs. Root hairs begin to appear at the epidermal cells at the farthest end of the region of cell elongation. But they become fully developed when the epidermal cells have reached their maximum length and have begun to differentiate. Thus, the region of cell maturation is also known as the root hair zone. The older root hairs die at the farthest end of the region of cell maturation. In the meantime, new root hairs are formed at about the same rate as the death of the old ones.
How Do Roots Absorb Water?
Below is the process of how substances are transported across a root. Water moves through roots primarily through diffusion and capillary action.
- From outside the root, water diffuses through the thin walls of the root and the rest of the cells in the root's epidermis.
- From the epidermal cells, it diffuses into the cells of the cortex. It moves by diffusion from cell to cell until it reaches the xylem vessels.
- Once inside the xylem vessels, it rises up the stem, primarily by capillary action.
Why Does Water Move Toward the Root's Center, Not Outward?
The tendency during diffusion is for a fluid's molecules to move from a region of greater concentration to a region of lesser concentration. There is usually more water per unit of volume in the epidermal cells than in the cells of the cortex. There is more water in the cortex than in the cells of the vascular cylinder. This creates a general movement of water in the root from outside inward.
Different Types of Roots
A common way to differentiate root types is by whether the root system is fibrous or a taproot system. However, there are also a few different types of specialized root systems that have developed to perform specific functions for plants. Some of these specialized root types include aerial, climbing, prop, and buttress roots.
Taproot Systems Vs. Fibrous Systems
In some plants, the primary root is very well-developed, resulting in what is known as the taproot system. The taproot may take the form of a fleshy root or a very long primary root. Fleshy taproots, such as carrot and radish, store food and water.
Plants with well-developed secondary roots have what is known as a diffuse or fibrous root system. Although fibrous roots are short, they spread over a large area. Water running along the surface of the ground is absorbed readily by them. The thick masses of roots are very efficient in preventing soil erosion. If you pull different kinds of weeds in the garden, you'll find out which of the two root systems is more common among weeds.
In some cases, as with cassava and sweet potato, the larger secondary roots become enlarged with stored food. Food, principally starch, is deposited in the large parenchyma cells of the cortex and vascular cylinder.
In general, roots absorb water and dissolved substances from the soil. The spongy aerial roots of orchids perform a more unusual feat—they absorb moisture from the air as well as from falling rain. Furthermore, the green aerial roots of orchids perform photosynthesis.
Roots anchor plants to the soil. This is accomplished by long roots and a great number of tiny rootlets that find their way between the soil particles deep under the ground. In the case of ivy and other vines, the climbing roots hold the stem securely to walls or tree trunks instead of to the ground. (The roots of aerial plants or epiphytes, such as orchids, do the same thing.)
In addition to ordinary roots, some plants have specialized roots that tend to reinforce the upright position of the stem. An example is the corn plant; it has roots that grow from the lower portion of the stem and prop up the tall plant. These are aptly called prop roots. Prop roots are valuable to tall and slender plants that have relatively shallow roots.
Buttress roots are exemplified by those of the tall kapok tree, with its thin and wide roots extending vertically from the base of the trunk. These roots are often found in areas of nutrient-poor, shallow soil, and they function to stabilize and buttress the tree by widening its foundation.
Uses of Roots to Humans
Preventing Soil Erosion
One of the ways in which humans most benefit from roots is in their prevention of soil erosion. Although soil erosion affects most of us only indirectly, it is nevertheless important to emphasize this function of roots as our forests are getting denuded by logging. Such wanton destruction of forest trees exposes the soil to erosion, which eventually carries the rich topsoil away to the sea.
Roots are used by people as a direct source of food. Sweet potato and cassava are common root crops in the Philippines. Our yam varieties include ube, tugi, and nami. Carrots and radishes are also used as vegetables. Singkamas is another juicy root that most Filipinos and other tropical countries are fond of. Other examples of roots used as food are parsnip, beetroot, and aroids, which belong to different botanical families.
Spices and Dyes
Roots are used to make spices and dyes. For example, sarsaparilla is a soft drink made from plants like Smilax ornata, commonly known as sarsi. Sarsaparilla is originally made from a blend of birch oil and sassafras, which is the dried root bark of the sassafras trees.
Roots are also used to make dyes; for instance, a "turkey-red" color is made from the root of madder.
Different roots are valued for a variety of medicinal uses. One medicinal root is chamomile, which is considered to be a cure-all. It is used as a sedative for anxiety disorders and relaxation.
Another medicinal root is turmeric. Turmeric root can cure a lot of internal organ problems such as arthritis, liver and gallbladder disorders, infections, and stomach problems. Some other roots that are considered medicinal are ginger root, maca root, valerian root, licorice, and coconut root.
Those are just a few of the amazing ways that roots are used by people. The different types and uses of roots go beyond what has been covered in this article. Many specific types of roots exist due to the ways they have evolved to help plants thrive in various settings.
© 2020 Ray
Eric Dierker from Spring Valley, CA. U.S.A. on March 08, 2020:
Extremely interesting. I thought I knew about roots. Very cool.