The xylem and phloem are tissues present in higher plants (vascular plants), that is, those that have a circulatory system. These two tissues are responsible for the transport of various substances.
While the xylem allows the transport of water and mineral salts, the phloem is responsible for the transport of sugars and other plant products.
The xylem is responsible for the upward transport, from the roots to the stem and leaves of the plants. Unlike xylem, phloem transport can be both upward and downward.
From what has been said above, it is then observed that xylem and phloem are two elements of the circulatory system of plants.
Both the term xylem and the term phloem come from Greek words. Xylem means wood, while phloem means bark.
Xylem is also known as firewood. For its part, the phloem is also called Liberian vessels, sieve tissue or bast.
General functions
The xylem and phloem are the components of the circulatory system of vascular plants. These two structures are responsible for connecting the upper part of the plant (stem, branches and leaves) with the lower part of it (roots).
The roots absorb water and minerals necessary for the plant to survive. However, from the roots to the top of the plants there is a considerable distance (depending on the size of the plant). This is where the xylem comes in.
Xylem
The xylem is made up of a series of vessels that connect the plant from one end to the other. These vessels guarantee the upward transport of the water at maximum speed.
The force to transport substances from one end of the plant to the other comes from two essential phenomena: osmosis and suction.
Osmosis occurs when the roots of the plants absorb water and move part of it towards the stem of the plant. However, the absorption force is not enough to make the water reach the leaves of the plant.
This is where suction comes in. This occurs when part of the water in the plant evaporates. This lack of water makes the tissues able to absorb water from neighboring tissues. In this way, the water reaches the top of the plant.
It should be noted that xylem not only intervenes in the transport of substances, but is also an important element for the support of the plant.
This is because the xylem is made up of a wall of lignified plant tissue, strong enough to give the plant stability.
Xylem can be seen when a tree is felled. When a tree has been cut down, a series of concentric rings can be seen. These rings are remnants of ancient xylem tissue.
The xylem tissue dies after one year and then a new xylem is formed. This is why each ring represents one year of the life of a tree.
The xylem is made up of three types of cells: tracheids, tracheas, and fibers. The tracheids are elongated and pointed in shape. Its cell wall is lignified, which gives it a hard and resistant consistency.
For their part, the tracheas are more specialized tracheids. These are arranged in a tubular shape to create the vessels that make up the xylem. Its function is transportation.
Finally, the fibers are thick formations (with lignified walls). Its function is not that of substance transport. Instead, they are tasked with providing additional support to the plant.
Phloem
Plants are autotrophic organisms, which means that they make their own food. This food (sugars) is generated through photosynthesis, a process that occurs in the leaves of plants.
The sugar produced thanks to photosynthesis must be distributed to all parts of the plant, since this is a source of energy. This is where the phloem comes in.
Phloem cells are found throughout the plant. These are responsible for transporting sugar and other molecules that have been created by photosynthesis.
Phloem is made up of two types of cells: sieve tubes and attached cells. The sieve tubes are elongated. They are made up of sieve cells that are organized vertically, one above the other.
These tubes have cell-cell divisions, the ends of which are perforated to allow the passage of various substances.
For their part, the attached cells are smaller than the sieve cells. They do not have a definite shape. These are in charge of regulating the activities of the sieve tubes.
Comparison chart between xylem and phloem
References
- Xylem and phloem. Retrieved on August 22, 2017, from bbc.co.uk
- Xylem. Retrieved on August 22, 2017, from wikipedia.org
- Phloem. Retrieved on August 22, 2017, from wikipedia.org
- Plhoem vs. Xylem. Retrieved on August 22, 2017, from diffen.com
- Vascular Tissue: Xylem and Phloem. Retrieved on August 22, 2017, from boundless.com
- Functions of xylem and phloem. Retrieved on August 22, 2017, from biology-igcse.weebly.com
- Xylem and Phloem. Retrieved on August 22, 2017, from basicbiology.net
- Xylem. Retrieved on August 22, 2017, from britannica.com
- Phloem. Retrieved on August 22, 2017, from britannica.com.