Vascular plants (from Latin vasculum : duct ) , also known as Tracheophyta ( tracheophytes / tr k i f aɪ t s / , from Greek αχεῖα α trācheia artēria ‘breathing tube’ + phutá ‘ plants’ ), making up a large group of plants ( c. 300,000 accepted known species) [5] whichare defined as land plants with lignified Tissue ( xylem ) for conducting water and minerals throughout the plant . They also have a specialized non-lignified tissue ( phloem ) to conduct the products of photosynthesis . Vascular plant include clubmosses , horsetails , ferns , gymnosperms (including conifers ) and angiosperms ( flowering plants ). The scientific name for the group includes Tracheophyta, [6] [4] : 251 Tracheobionta [7] and Equisetopsida sensu Lato ., Some early land plants ( rhinophytes ) had less developed vascular tissue; The term eutrachophyte has been used for all other vascular plants.
features
Botanists define vascular plants by three primary characteristics:
- Vascular plants have vascular tissues that distribute resources through the plant. There are two types of vascular tissue found in plants: xylem and phloem. Phloem and xylem are closely related to each other and are usually located adjacent to each other in the plant. The combination of a xylem and a phloem strand adjacent to each other is known as a vascular bundle. [8] Evolution allowed the size of vascular tissue in plants to grow to larger sizes than those of non-vascular plants, which lack these specialized conducting tissues and are thus restricted to relatively small sizes.
- In the vascular plant, the principal generation stage is the sporophyte , which produces spores and is diploid (having two sets of chromosomes per cell). (In contrast, the dominant generation stage in nonvascular plants is the gametophyte , which produces gametes and is haploid—with one set of chromosomes per cell.)
- Vascular plants have true roots, leaves, and stems, even though some groups have lost one or more of these traits.
Cavalier-Smith (1998) treated the Trachophyta as a phylum or botanical division that encompasses these two features as defined by the Latin phrase “Phases diploida xylem et phloem instructa” (diploid stage with xylem and phloem). [4] : 251
One possible mechanism for emphasizing diploid generation from the emphasis on haploid generation for predictive evolution is greater efficiency in spore dispersal with more complex diploid structures. The expansion of the spore stalk enabled the production of more spores and the evolution of the ability to release them higher and propagate them further. Such growth may include more photosynthetic areas for the spore-bearing structure, the ability to develop independent roots, a wood structure for support, and more branching.
nutrient delivery
Water and nutrients in the form of inorganic solutes are drawn from the soil by the roots and carried through the xylem to the whole plant. Organic compounds such as sucrose produced by photosynthesis in leaves are delivered by phloem sieve tube elements.
Xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall usually consists of the polymer lignin. However, the phloem consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates that have pores to allow molecules to pass through. Sieve-tube members lack organelles such as nuclei or ribosomes, but the cells next to them, the companion cells, function to keep the sieve-tube members alive.
sweat
The most abundant compound in all plants, as in all cellular organisms, is water, which plays an important structural role and plays an important role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is continuously transported from the plant to the atmosphere through its stomata and is replaced by soil water taken up by the roots. The movement of water from the leaf stomata creates a transpiration stretch or tension in the water column in the xylem vessels or tracheids. Stretching is the result of surface tension of water within the cell wall of mesophyll cells, from whose surfaces the stomata are open when evaporation occurs. Hydrogen bonds exist between water molecules, causing them to line up; As the molecules at the top of the plant evaporate, Each pulls up to replace the next one, which in turn draws the next one in line. The upward pull of water may be completely passive and may be facilitated by the movement of water to the roots via osmosis. As a result, transpiration requires very little energy to be used by the plant. Transpiration helps the plant to absorb nutrients from the soil in the form of soluble salts.
absorption
Living root cells passively absorb water by creating root pressure through osmosis in the absence of transpiration. It is possible that there is no evaporation and therefore no water pull towards the shoots and leaves. It is usually caused by high temperature, high humidity, darkness or drought.
conduction
Xylem and phloem tissues are involved in conduction processes within plants. Sugars are carried throughout the plant through the xylem into the phloem, water and other nutrients. There is conductance from one source to one sink for each different nutrient. Sugars are produced in leaves (a source) by photosynthesis and transported to growing shoots and roots (sinks) for use in growth, cellular respiration or storage. The minerals are absorbed into the roots (a source) and transported to the shoots to allow for cell division and growth.
