Xylem and Phloem Differences and Similarities

What are Xylem and Phloem?

In plants, there are different plant tissues which include the reproductive tissue, meristematic tissues, and permanent tissues. The complex permanent tissues are the vascular tissues which include the xylem and phloem. They are the two transport tissues of plants. They are present in all vascular plants including angiosperms, ferns, horsetails, seedless club mosses, and gymnosperms.

The xylem of plants is the vascular tissue that transports water and nutrients from the root of the plant to other parts of the plant such as leaves and stems. Xylem gives support to other tissues that are soft in vascular plants and is what distinguishes a vascular plant from a nonvascular plant.

The phloem of plants is the vascular tissue that transports organic nutrients from the site of photosynthesis (leaves) to other parts of the plant. It transports sucrose and amino acids up and down the plant through the process called translocation.

These plant tissues are therefore the two main types of vascular tissues that carry out the transportation process in plants. They create a vascular bundle that works together as a unit. However, there are differences between them.

Structure

The xylem and phloem structure is made up of cells. The mature xylem contains elongated dead cells that are arranged from end to end in order to form vessels. These mature xylem vessels have no cytoplasm and are impermeable to water. The walls of the xylem are tough and contain a woody material called lignin. Xylem is made of the following elements:

  1. Tracheids
  2. Vessel elements
  3. Xylem parenchyma
  4. Xylem fibers

Phloem is made up of living cells that are arranged end to end. The xylem and phloem structure differs in that the phloem vessels have cytoplasm, unlike the xylem vessels. Their vessels go through holes from one cell to another. Phloem is made of the following elements:

  1. Sieve elements (conducting phloem cells)
  2. Parenchyma cells (companion cells and albuminous cells)
  3. Supportive cells ( bast fibers and Sclereids)

Diagram of Xylem and Phloem

The cross section diagram of the Basswood stem showing the xylem and phloem
A cross-section diagram of the Basswood stem showing the xylem and phloem

Functions of xylem and phloem

  • Xylem is responsible for giving the plant support and replacing the water molecules lost during transpiration.
  • Phloem is responsible for translocation.
  • The xylem and phloem functioning in plants is essential as xylem transport water from the root to the leaves and stems while the phloem transport food from the leaves to other parts of the plant.

Here are videos explaining the function of the xylem and phloem in plants

Xylem vs Phloem

Similarities

  • The cell walls of the xylem and phloem consist of cellulose.
  • They both contain chloroplast.
  • Phloem and xylem function in the transportation process that occurs in vascular plants.
  • They both exhibit primary and secondary growth.
  • These tissues both contain more than one type of cell.
  • They both develop from the cambium.
  • They both possess fibers.
  • These tissues are both differentiated into proto- and meta-elements.
  • They both possess parenchymatous cells.

Phloem and Xylem differences

A major difference between the xylem and phloem can be seen in their movement. The movement of the xylem in a plant is unidirectional whereas, the movement of the phloem in a plant is bidirectional.

Another difference between xylem and phloem is the function they play in the transportation system of plants. In vascular plants, the xylem functions in the transportation of water and provides support to the plant. Its presence in a vascular plant is the reason why they grow higher than nonvascular plants. Phloem, on the other hand,  transport nutrients such as sugar, organic molecules, and proteins in vascular plants, which enable the plant to stay alive and reproduce.

Hence, the main function of the xylem is to transport water and minerals from the roots to other parts of the plants whereas, the phloem transport nutrients and food from the leaves of the plant to other parts of the plant.

Here is a table that summarizes the contrast of xylem vs phloem.

A table showing the differences between phloem and xylem

Phloem vs Xylem
Phloem Xylem
Structure  The phloem tissues have a tubular-shaped structure that is elongated. The xylem tissues have a tubular-shaped structure or a structure that appear to be star-like
Cell wall The tissues have walls with thin sieve tubes Absence of cross walls
Location Phloem location is on the outer side of the vascular bundle The xylem location is in the center of the vascular bundle
Movement The movement of the phloem in a plant is bidirectional which means that it moves both ways (up and down) The movement of this tissue in a plant is unidirectional which means that it moves in only one direction which is upwards.
Fibers   Phloem fibers are larger in size Xylem fibers are smaller in size
Mechanism For the phloem, to carry out the conduction of food, adenosine triphosphate (ATP–a form of energy) is required This tissue through transpiration pull conducts water. This transpirational pull is a physical force that pulls water from roots
Presence in plants In plants, they are present in the leaves and stems which are later transported and grow in the fruits, roots, and seeds of the plant They are present in the stems, roots, and leaves of the plant
Elements Phloem is made of the following elements:

  1. Companion cells
  2. Bast fibers
  3. Sieve tubes
  4. Phloem fibers
  5. Intermediary cells
  6. Phloem parenchyma
Xylem is made of the following elements:

  1. Tracheids
  2. Vessel elements
  3. Xylem parenchyma
  4. Xylem fibers
Total number of tissue The total number of phloem tissue is lesser The total number of xylem tissue is more than the total number of phloem tissue
Function Phloem transport nutrients and food such as amino acids, sugar, and protein from the leaves of the plant to other growing parts of the plant and storage organs Xylem transport water and soluble minerals from the roots  of the plant to the aerial parts of the plants
Function These tissues translocate the synthesized sugars from the photosynthetic areas of plants. The sugar is transported to storage organs such as tubers, roots, and bulbs These tissues give mechanical strength to the plant and aid in strengthening the stem.
Role Phloem is primarily responsible for the transportation of mRNAs and proteins throughout the plant This tissue is primarily responsible for the replacement of the total amount of water molecules that are lost through photosynthesis and transpiration

 

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