The Raw sap Is an aqueous solution of thick consistency that circulates through the vascular system of a plant. It is the juice of plants of any kind, especially the juices ascending and descending or circulating fluids essential for the nutrition of the plant.
The ascending sap is the raw sap, whose assimilation takes place in the leaves, when it becomes the sap elaborated suitable for the growth of the plant.
The raw sap is composed of plant regulators (plant-type hormones that regulate the growth of plants), minerals and water obtained from the soil, which is processed in the leaves and distributed throughout the plant in the form of processed sap.
Sage contains sugars, vitamins, minerals, proteins and fatty acids that allow you to develop all your growth and fruiting processes.
Plants also secrete other liquids that are often confused with raw sap; Latex, resins or mucilage.
Plants have two different types of tissues to transport the sap. The Xylem is the tissue that transports the raw sap or ascending sap from the roots to the leaves, and the phloem conveys the sap made from the leaves to the rest of the plant.
The Xylem and Phloem
The xylem is a composite tissue in vascular plants that helps provide support and that leads the raw sap upward from the roots. It is composed of tracheids, vessels, parenchyma cells and wood fibers.
The xylem participates in the support and reserve of nutrients, besides taking care of the conduction of the minerals. Its structure is tubular in shape, with no crossed walls that allow a continuous column of water and facilitates faster transport within the vessels.
It is unidirectional (moves the stem of the plant) and responsible for replacing the water lost by perspiration and photosynthesis.
On the other hand, the phloem transports the sap made from green leaves and stems to the root. This wise elaborated is composed of minerals, sugars, phytorregulators and water.
The circulation of the wise: Cohesion-tension theory
The circulation of the raw sap through the plants is based on this theory. The cohesion-tension theory is an intermolecular attraction theory that explains the process of water flow upwards (against the force of gravity) through the xylem of plants.
This theory was proposed by the botanist Henry Dixon in 1939. It states that the raw sap in the xylem is drawn up by the drying power of the air, which creates a continuous negative pressure called tension.
The tension extends from the leaves to the roots. Most of the water that a plant absorbs is lost by evaporation, typically from stomata on the leaves of the plant, a process called transpiration.
Perspiration places negative pressure (pulls) on continuous columns of water that fill the narrow conducting xylem tubes. A water column resists breaking in droplets as it moves through a narrow duct like the xylem tube (water molecules are connected by hydrogen bond).
Thus, the negative pressure created by the transpiration (tension) pulls the entire column of water that fills the xylem tube. It is then, due to osmosis, that the raw sap reaches the xylem of the roots of a plant.
The water molecules are linked together by hydrogen bonds, therefore the water forms a chain of molecules during their movement towards the xylem. Water molecules stick together and stop by force called tension. This force is exerted due to evaporation on the surface of the blade.
There is another theory that explains the transport of the raw sap called the root pressure theory.
Root pressure is basically the idea that a plant's roots can maintain a higher or lower pressure based on its surroundings. It does so in order to promote or discourage nutrient absorption.
In other words, the root system of a plant can alter its pressure to: a) help the raw sap increase along the plant, or b) push the raw sap out of the plant.
Explanation of water movement in a plant
As the raw sap enters the roots through osmosis, xylem cells fill and swell, putting pressure on the outermost rigid cells of the root.
This pressure, especially when the levels are low outside the plant, causes the sap to be forced to climb to the plant, despite the force of gravity.
The electric charge of these cells from the outer root creates a kind of"one-way path"that does not allow the raw sap back and forth from the roots.
Root pressure was determined to be a pressure developed on the xylem tracheal elements as a result of the metabolic activities of the root. It is said that the pressure of the root is an active process that is confirmed by the following facts:
- Living cells are essential in the root so that the root pressure develops.
-Oxygen supply and some metabolic inhibitors affect root pressure without affecting the semi-permeability of membrane systems.
- Minerals accumulated against the concentration gradient by active absorption using metabolically generated energy reduce the water potential of the surrounding cells, leading to the entry of crude sap into the cells.
The transpiration traction is responsible for the ascent of the sap in the xylem. This rise of sap depends on the following physical factors:
- Cohesion - Mutual attraction between molecules of water or raw sap.
- Surface tension - Responsible for the greatest attraction between molecules of water or crude sap in liquid phase.
- Adhesion - Attracting molecules of water or raw sap on polar surfaces.
- Capillarity - Ability to raise the raw sap in thin tubes.
These physical properties of the sap allow you to move against gravity in the xylem.
The elaborated sap
Substances taken from the soil through the root (water and mineral salts) form the raw sap. It rises from the roots to the leaves through the stem.
The leaves are responsible for transforming raw sap into the processed sap which is poorer in water and richer in nutrients due to the function of chlorophyll.
The elaborated sap descends to the root to feed the plant. Needs photosynthesis to form, however, the raw sap is created without photosynthesis.
Composition of the phloem sap or elaborated sap
The main components of the phloem sap are carbohydrates. Analyzes of phloem exudates from various plants have shown that sucrose is the main carrier form of carbohydrates.
In some species of Cucurbitaceae, in addition to sucrose, some oligosaccharides such as raffinose, stachyose and verbascosa have also been found in the composition of phloem or processed sap.
In some cases sugar alcohols mannitol and sorbitol or dulcitol have been found in phloem exudates.
Generally, algae produce large amounts of mannitol. Phloem exudation rarely contains hexoses although glucose and fructose are commonly present in felogenous tissue.
References
- Sha, R. (2016). Phloem Sap Composition. 10-1-2017, from Biology Discussion Website: biologydiscussion.com.
- TutorVista. (2016). Theories for Ascent of Sap. 10-1-2017, from TutorVista Website: tutorvista.com.
- TutorVista. (2016). Cohesion Adhesion Tension Theory. 10-1-2017, from TutorVista Website: tutorvista.com.
- Diffen. (2015). Phloem Vs. Xylem. 10-1-2017, from Diffen Website: diffen.com.