Plants need nutrients and water pumped throughout their stems, roots, and leaves. In this lesson, we will learn about the function of vascular bundles, the different types, and test your knowledge with a short quiz.
What Are Vascular Bundles?
Look down at the underside of your arms.
Chances are you can see some of your veins, carrying blood down to your hands and back to your heart. Your veins, arteries, and capillaries are an example of vascular tissue, tissue that carries life-sustaining substances through the body of an organism. Our vascular tissue transports blood, which carries nutrients, hormones, immune cells, and a whole mix of other substances essential to optimum body functioning.Plants also have vascular tissue.
Only instead of blood, their tissues transport water and nutrients that are pumped through the plant’s whole structure, often against gravity. While our veins are spread around our other internal body parts, like bones and muscle, plant vascular tissue is arranged in vascular bundles. You can see these bundles if you cut a piece of celery in half, and look at the cross section, shown in this image. The bundles run through the plant like straws.
Just like you have veins, arteries, and capillaries, plants have several different tissue types that make up their vascular bundles.
Xylem is tissue that is responsible for transporting water and nutrients through the plant. Phloem is tissue that transports larger, organic molecules through the plant. Think of them as ‘drinking’ and ‘eating’ tubes, respectively. The plant tissues that make up the bulk of the ‘filling’ spaces in plants are known as parenchyma, which grows with the plant and also helps in the storage of various substances. Also involved in growth is the cambium tissue, which creates new xylem and phloem as the plant stems increase in girth. All of these tissues serve to ensure that critical substances are transported through the plant.
Types of Bundle Arrangements
The vascular bundles are arranged differently in plants, depending on their internal structure.
Plants classified as dicots have two initial seed leaves when they germinate, a single taproot, and branched leaves, developing into plants such as magnolia trees, oak trees, cotton, coffee beans, legumes, lettuce, and daisies. Their vascular bundles are arranged in a circle within the stem, with phloem on the outside, xylem on the inside, and a layer of cambium in between each bundle. It is xylem in these plants that can later become woody tissue, in many cases.Plants classified as monocots have one initial seed leaf when they germinate, a branched root system, and parallel leaf veins, developing into plants such as grains, sugar, lilies, banana trees, daffodils, and grasses.
Their vascular bundles are arranged in a more scattered fashion within the stem. They also have cambium in between the xylem and phloem, and parenchyma cells fill in the rest of the space. Monocots do not develop woody tissue.
Vascular bundles are a collection of tube-like tissues that flow through plants, transporting critical substances to various parts of the plant. Xylem transports water and nutrients, phloem transports organic molecules, and cambium is involved in plant growth. The arrangement of the bundles is circular in dicots and scattered in monocots. Without vascular bundles, plants could not ‘eat,’ ‘drink,’ or grow, much the same way our bodies could not function without similar vascular tissues.