Phloem
Phloem
Phloem (/ˈfloʊ.əm/, from the Greek φλοιός phloios "bark") is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation.
Etymology
The term "phloem" is derived from the Greek word φλοιός (phloios), which means "bark". This is because in trees, the phloem is the innermost layer of the bark.
Structure
Phloem is composed of several cell types including sieve elements, companion cells, phloem parenchyma, and phloem fibres. The primary components of phloem are the sieve elements and the companion cells.
Sieve Elements
Sieve elements are the type of cell that are responsible for transporting sugars throughout the plant. They have a unique structure, with a sieve plate at each end of the cell that allows for the movement of sugars and other substances.
Companion Cells
Companion cells are found alongside sieve elements and provide them with metabolic support. They are responsible for loading and unloading sugars into the sieve elements.
Phloem Parenchyma
Phloem parenchyma cells, also known as transfer cells and border parenchyma cells, are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they also function in the transport of foods.
Phloem Fibres
Phloem fibres are supportive cells that provide strength and support to the phloem tissue. They are typically long, slender cells that have thick walls and a small lumen (the inside space of a cell).
Function
The primary function of the phloem is to transport the products of photosynthesis (sugars) from the leaf cells where they are produced to other parts of the plant where they are needed or stored. This process is known as translocation.
Related Terms
External links
- Medical encyclopedia article on Phloem
- Wikipedia's article - Phloem
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