Absorption of water
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| Agriraghv |
Water in the atmosphere😊
The electromagnetic interactions with ice, snow, and clouds are determined by the refractive index and absorption coefficient of pure ice plus the reflectance, absorbance and transmittance effects of grain size (for snow), bubbles (for glacier and lake ices), brine inclusions (for sea ice) and impurities (for clouds) [3580]. Clouds contain smaller ice crystals than snow plus dust and soot. The spectrum of ice resembles (but is not identical to) that of water (see below) except in the far-infrared, microwave and radio-wave regions (particularly <~20 cm-1). The grain size of snow determines its reflectance with larger crystals showing poorer reflectance (poorer aldebo) and greater absorbance. Ice is blue (like liquid water, see below) but snow is white. Snow and ice are transparent to radio waves with radar able to determine ice-sheet thickness. Ordinary ice is birefringent .
Active absorption
Active absorption refers to the absorption of water by roots with the help of adenosine triphosphate, generated by the root respiration: as the root cells actively take part in the process, it is called active absorption. According to Renner, active absorption takes place in low transpiring and well-watered plants, and 4% of total water absorption is carried out in this process. The active absorption is carried out by two theories; active osmotic water absorption and Active non-osmotic water absorption. In this process, energy is not required.
Passive absorption of water
This mechanism is carried out without utilisation of metabolic energy. Here, only the roots act as an organ of absorption or passage. Hence, sometimes it is called water absorption 'through roots', rather 'by' roots. It occurs in rapidly transpiring plants during the daytime, because of the opening of stomata and the atmospheric conditions. The force for absorption of water is created at the leaf end i.e. the transpiration pull. The main cause behind this transpiration pull, water is lifted up in the plant axis like a bucket of water is lifted by a person from a well. Transpiration pull is responsible for dragging water at the leaf end, the pull or force is transmitted down to the root through column of water in the xylem elements. The continuity of the water column remains intact due to the cohesion between the molecules and it act as a rope. Roots simply act as a passive organ of absorption. As transpiration proceeds, water absorption occurs simultaneously to compensate the water loss from the leaf end. Most volume of water entering plants is by means of passive absorption. Passive transport is no different from diffusion, it requires no input of energy: there is free movement of molecules from their higher concentration to their lower concentration. The water will enter the plant via the root cells that can be found in the roots where mainly passive absorption occurs. Also, with the absorption of water, minerals and nutrients are also absorbed.
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