Process for the production of energy-rich biomolecules using light energy. Responsible for this are the chloroplasts (organ cells) in which the chlorophyll (leaf green) is found. Dyes such as chlorophyll, carotenoids and flavonoids in leaves or other green parts of plants use solar radiation as an energy source to produce carbohydrate compounds. This process converts carbon dioxide from the air and water into the carbohydrates glucose and fructose, while elemental oxygen is released. The uptake of solar energy by plants results in the binding of around 150 billion tonnes of carbon dioxide and the release of 400 billion tonnes of oxygen every year on Earth.
In contrast to assimilation, the reverse process is dissimilation or respiration, in which sugar and oxygen are consumed to form carbon dioxide and water, releasing energy. In a cycle of 200 years each, all the carbon dioxide in the atmosphere is bound in a biochemical cycle in the carbon compounds of plants, fungi and animals in order to be released again as a gas when microorganisms decompose them. From the primary carbohydrates glucose and fructose formed by photosynthesis and their storage form starch as well as nutrient salts and trace elements absorbed by the roots, all substances necessary for the plant life process are derived (assimilates, secondary plant substances). Nutrient and water transport are separated in the plant.
The active transport of sugar from the leaves through the plant's leading tissue takes place in the transport form of sucrose through the phloem. Together with the xylem, this forms the two-membered leading tissue. Through the xylem, the passive transport of water with the transpiration suction from the roots to the stomata of the leaves takes place. Excess sugar is stored by the phloem in the berries, stem and roots. In the berries, the inflow of water is blocked after the berries have reached their full size in order to prevent the berry from bursting due to the strong osmotic effect of the sugar. Important factors for an optimal photosynthesis and sugar production are sufficient sunlight, warm temperatures (ideal for leaves are 15 to 30 °C), a regulated water balance with a balanced relationship between water withdrawal and water storage capacity in the soil, as well as sufficient air humidity (optimal 60 to 70%).
Important nutrients for the plants are boron, iron, magnesium, sulphur and nitrogen. These are essential for the functioning of the chlorophyll, which absorbs and converts the energy of the sun so that photosynthesis can be set in motion. Carbon dioxide is absorbed through small, sealable pores (stomata) in the epidermis of the undersides of the leaves. The oxygen and water vapour produced during photosynthesis is also released through these pores. The biochemical process of photosynthesis is, so to speak, the first step in vinification.
During fermentation, the yeasts convert the plant-produced sugar into alcohol and carbon dioxide. Ultimately, the human cycle is closed by the consumption of wine, whereby the alcohol is burned in metabolism and converted back into water, energy and carbon dioxide. The maximisation of the photosynthesis performance is the central goal of many viticultural measures (such as targeted leaf care), as this directly determines the amount of sugar stored in the grapes. In case of heat stress (above 40 °C) and drought, photosynthesis is stopped. Respiration, which is consumed by oxygen and carbon dioxide is released, can be described as the weight of photosynthesis.
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