Gardeners are always particular about watering their plants; that’s what helps them grow. But, you aim to provide moisture to the soil. So, how does the water in the soil travel up the tall trees to nourish the stems and leaves for lush growth?
This is why plants have their built-in transport system to transport water, minerals, and nutrients. And they do this against gravity, up the trunk, onto the branches, stems, leaves, and everywhere else where it’s needed.
Vascular plants have two types of transport tissues for transporting substances around the plant, xylem and phloem. Phloem transports the food synthesized during photosynthesis from the green parts to the rest of the plant. Xylem is the other vital part of the plant’s transport system. Of course, both are equally essential tissues for a plant’s healthy life, but we’ll explore the xylem’s role in a plant’s life in this post.
What does xylem transport? Are there any other benefits? How does it function? There is plenty more about xylem’s humble contributions to plant growth that you still don’t know. With this post, we’ve put together a detailed profile of this specialized tissue so you can understand what xylem is all about and realize its importance for plants.
What Is The Xylem Of The Plant And What Does It Do?
Think of xylem as the plumbing of the plant. Just like our home’s plumbing carries water around the house to the taps of kitchens and bathrooms, xylem carries water to where it’s needed.
Xylem is like the plumbing system of the plant.
In more scientific words, xylem is the plant vascular tissue responsible for carrying water from the root-soil interface to the plants’ above-ground parts. Since water is the primary solvent for plants’ nutrition, the minerals dissolved in the water drawn by the roots are also carried up through the xylem. Alongside phloem, xylem is found in all vascular plants, including ferns, gymnosperms, clubmosses, horsetails, and angiosperms.
How To Identify Xylem In Plants?
You already know that xylem transports water. So when you water the plants, water will go wherever the xylem cells take it. You can work around the concept to pinpoint xylem of the plant. It can turn out into an inspiring project for a science class. Do it with your kids at home, and they’ll be thoroughly intrigued.
Here’s An Experiment To Identify Xylem In A Celery Stick!
Just take a short piece of celery with the leaves still attached. Place it upright in a container that has colored water. Leave it for a day or two before cutting lengthwise through the stalk. The color path highlights the plant’s xylem since that’s the route the colored water will follow.
Want multi-colored celery? Split the lower part of the stalk and place it in two trays, each with different food color added to the water, and present a colorful celery dish to the family later that day!
What Are The Functions Of Xylem?
The xylem is made up of specialized water-conducting xylem cells, also called tracheary elements. These cells provide the interior hydrophobic surface that assists in water transportation against gravity to different plant parts. Dissolved minerals also take the same route along with the water.
Though water and nutrient transport is the primary function of the xylem, it offers other benefits too. For example, the same water-conducting cells that form the transport system also provide the plant mechanical support.
So the tall plants you see standing upright on the ground also have the xylem to thank for. The xylem cells support the weight of the water that’s being carried upwards and the weight of the plant itself.
In older plants and trees, xylem is wood, one of the most abundant and treasured raw materials for humans. The structure and distribution of xylem cells result in the varying properties of different kinds of wood.
What Is The Structure Of Xylem?
Xylem is made of several kinds of cells. The major ones are the tracheary elements that help transport water. The two types of tracheary elements are:
Tracheids are longer than vessel elements and help transport xylem sap. They also give the plant its structural support.
2. Vessel Elements
Vessel elements present in flowering plants are shorter than tracheids and are connected by perforation plates. They are the ones responsible for conducting water up the plant.
Besides the tracheary elements, xylem also contains parenchyma and long fibers. Fibers contribute to the plant’s structural support. Parenchyma is an abundantly present tissue in plants used for storing various substances. Most of the soft parts in a plant are made of parenchyma.
Where Can You Find Xylem?
Xylem is present in vascular bundles that are present in non-woody plants. So you’ll also find them in non-woody parts of the woody plants. Other than that, it’s a part of the secondary xylem formed by the vascular cambium in woody plants. It’s also present in the stele of ferns and other vascular plants. The dead cells of the xylem contribute to form the woody parts of the plants.
What Does Xylem Look Like?
If you want to see what a plant’s xylem looks like, the celery experiment described above, when seen under a microscope, the star-shaped structure in a stem’s cross-section is the xylem.
Types Of Xylem
Two forms of xylem are present in plants. Their function is the same: to transport water and minerals but are named differently by the type of growth that creates them.
1. Primary Xylem
Primary xylem is created with the plant’s primary growth, occurring at the tips of the stems, roots, and new flowers. With the development of the primary xylem, the plants grow taller, and the roots grow longer. It’s called primary because the primary growth precedes the secondary growth during the growing season.
2. Secondary Xylem
The secondary xylem forms with the plant’s secondary growth and contributes to the plant’s increasing width over time. Secondary growth occurs each year after primary growth and increases the tree trunk’s width over the years. The dark concentric rings in the tree trunk’s cross-section that are also used to determine the tree’s age come from the secondary xylem.
Tracking The Route Of Water – Roots To The Shoots
We know that xylem’s primary function is to transport water and dissolved minerals through the plants. But how does the water flow upwards, against the pull of gravity, from the roots to the shoots? Since you don’t see any pump at the tree’s base to push the water upwards, what powers the plants’ transport system?
Three phenomena’s contribute to the upwards flow of water:
Root pressure relies on water movement from the soil into the roots through osmosis due to the higher water concentrations in the growing medium. The higher pressure of water coming into the roots pushes it up towards the stems and branches. But, root pressure will only push the water up by a limited distance. On its own, it cannot pull water all the way up in tall trees.
2. Transpirational Pull
Transpiration is the evaporation of water from the exposed surfaces of the plants through the stomata. This water removal from the plant creates a negative water pressure towards the plant’s leaves and stems.
A pulling force forms, sucking water through the xylem vessels from the bottom of the plant towards the top. This force is called the transpirational pull. Transpirational pull increases in hot, dry weather when the evaporation rates are higher.
3. Capillary Action
Capillary action is the liquid’s movement across a solid surface caused by the adhesion between the “unlike” molecules. Also, the water molecules are attracted to each other, which is called cohesion.
Both of these properties cause the water to move up the xylem vessels through vertical stems. On its own, capillary action can push water up the stem by about 3,3 feet (about 1 meter). But, it’s still not strong enough to move liquid up a tall tree.
When working together, these three hypotheses create a potent force that moves the water and minerals upwards through the tall trees to the stems and leaves for lush green growth.
That was an overview of why do plants need xylem. To sum up the entire concept, it’s a vital component in vascular plants that transports water and essential nutrients to all the parts of the plant and gives it the necessary support. It ensures a healthy and robust plant and is immensely important to the plant’s development.