By: Tony Wang
Plants, like animals, are composed of several different organs, tissues, and cells, each with varying degrees of complexity. Each of these functional units help a plant do two things: stay alive and reproduce.
Let’s start with the most common plant organ: roots. A root is an organ that anchors a vascular plant into the soil, absorbs nutrients and water, and stores carbohydrates. Vascular plants are plants that have xylem and phloem. Vascular plants are able to grow higher than other plants due to the rigidity of their xylem cells. Furthermore, tall plants with large shoot masses generally have a taproot system, which consists of one main vertical root, better known as the taproot, which penetrates the soil deeply and helps prevent the plant from toppling.
Another plant organ is the stem. A stem is a plant organ bearing leaves and buds. Each stem consists of an alternating system of nodes and internodes. Nodes are the points at which leaves are attached to the stem, and internodes are the segments of stem between the nodes.
A stem’s chief function is to elongate and orientate the shoot in a way that maximizes the photosynthesis potential of the leaves. Another function of plant stems is to elevate the plant’s reproductive structures, which essentially means to facilitate the dispersal of pollen and fruit. Additionally, some green plant stems can perform a limited degree of photosynthesis.
Let’s now talk about leaves. In most vascular plants, the leaf is the organ primarily responsible for photosynthesis. In addition to this, leaves also intercept light, exchange gases with the atmosphere, dissipate heat, and defend the plant from herbivores and pathogens. Leaves consist of a flattened blade and a stalk, both of which joins the leaf to the stem at a node.
Another intriguing tissue that plants have is the dermal tissue system. The dermal tissue system is a plant’s outer protective covering. Like our skin, it forms the first line of defense against physical damage and pathogens. In nonwoody plants, it consists of a single layer of tissue called the epidermis. However, the dermal tissue system is more advanced than just that. In leaves and most stems, there is a waxy coating on the epidermal surface, known as the cuticle. The cuticle helps prevent water loss, which in turn, aids the plant in surviving.
Overall, plants are composed of dozens of unique functional units, each of which serve a specific function that plays a role in the plant's development and survival. These units are a result of millions of years of evolution, and are sure to continue to evolve long into the future.
What Did You Learn?
1. What are the functions of the xylem and the phloem?
The two types of vascular plant tissues are xylem and phloem. Xylem tissue conducts water and dissolved minerals upward from the roots of a plant into its shoots. Phloem tissue transports sugars, the products of photosynthesis, from where they are made (typically the leaves) to where they are needed or stored—usually roots and sites of growth, such as developing leaves and fruits.
2. What does the structure of a plant lead look like?
Because there are so many different types of plants, leaf structure often varies extensively. In general, however, a leaf consists of a flattened blade and a stalk, the petiole, which connects the leaf to the stem at a node. However, grasses and many other plants lack petioles. Instead, the base of the plant forms a sheath that envelops the entire stem.