Tracheid
Encyclopedia
Tracheids are elongated cell
s in the xylem
of vascular plant
s that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel element
s being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast
has broken down and disappeared. The presence of tracheary elements is the defining characteristic of vascular plants to differentiate them from non-vascular plant
s. Tracheid build varies by location.
The two major functions that tracheids may fulfill are
In most cases, the prime function of tracheids is transporting water. They occur in vascular bundle
s throughout the non-woody parts of the vascular plant and provide water and minerals collected by the roots to leaves and other parts of the plant (stem, flowers, fruits etc).
A good example of structural support is in softwood
s where tracheids are the major cell type. Tracheids give softwood its strength.
Because tracheids have a much higher surface to volume ratio compared to vessel elements, they serve to hold water against gravity (by adhesion
) when transpiration
is not occurring. This is likely one mechanism that helps plants prevent air embolism
s.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s in the xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
of vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel element
Vessel element
A vessel element is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers....
s being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast
Protoplast
Protoplast, from the ancient Greek πρῶτον + verb πλάθω or πλάττω , initially referred to the first organized body of a species.Protoplast has several biological definitions:...
has broken down and disappeared. The presence of tracheary elements is the defining characteristic of vascular plants to differentiate them from non-vascular plant
Non-vascular plant
Non-vascular plants is a general term for those plants without a vascular system . Although non-vascular plants lack these particular tissues, a number of non-vascular plants possess tissues specialized for internal transport of water....
s. Tracheid build varies by location.
The two major functions that tracheids may fulfill are
- part of the transport system
- structural support
In most cases, the prime function of tracheids is transporting water. They occur in vascular bundle
Vascular bundle
A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues...
s throughout the non-woody parts of the vascular plant and provide water and minerals collected by the roots to leaves and other parts of the plant (stem, flowers, fruits etc).
A good example of structural support is in softwood
Softwood
The term softwood is used to describe wood from trees that are known as gymnosperms.Conifers are an example. It may also be used to describe trees, which tend to be evergreen, notable exceptions being bald cypress and the larches....
s where tracheids are the major cell type. Tracheids give softwood its strength.
Because tracheids have a much higher surface to volume ratio compared to vessel elements, they serve to hold water against gravity (by adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
) when transpiration
Transpiration
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...
is not occurring. This is likely one mechanism that helps plants prevent air embolism
Air embolism
An air embolism, or more generally gas embolism, is a pathological condition caused by gas bubbles in a vascular system. The most common context is a human body, in which case it refers to gas bubbles in the bloodstream...
s.
External links
- Pictures of softwood tracheids in cross section and in maceration; both in pine.