Biological Sciences
Water Loss
Water loss refers to the process by which organisms release water from their bodies. This can occur through various means such as evaporation from the skin or respiratory surfaces, excretion, and sweating. In biological systems, maintaining water balance is crucial for proper physiological functioning, and excessive water loss can lead to dehydration and other health issues.
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5 Key excerpts on "Water Loss"
eBook - PDF- Paul Kramer(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
On the other hand, rapidly transpiring plants lose so much water on sunny days that the cells of young twigs and leaves lose turgor and wilt, stomata close reducing Transpiration 409 photosynthesis, and growth is reduced or stopped. The harmful effects of water stress will be discussed further in Chapters 13 and 16. We regard transpiration as an unavoid-able evil, unavoidable because of the structure of leaves and evil because it often produces water deficits and causes injury and death by desiccation. The Process of Transpiration Because of the great importance of transpiration in the overall water economy of plants, the nature of the process and the factors affecting it deserve careful attention. Transpiration is basically the physical process of evaporation which is controlled by physical factors. However, transpiration is also a physiological process, and as such it is affected by plant factors such as leaf structure and exposure and the behavior of stomata. It usually occurs in two stages, evaporation of water from cell walls into intercellular spaces and the diffusion of water vapor into the outside air. Transpiration as a Physical Process The rate of evaporation of water from any surface depends on the energy supply available to vaporize water, the vapor pressure or vapor concentration gradient that constitutes the driving force, and the resistances in the diffusion pathway. Most water vapor escapes through the stomata, some passes out through the epidermis of leaves and its cuticular covering, and some escapes from the lenticels in the bark of branches and twigs of woody species.
eBook - PDF- Morris Rockstein(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
However, in spite of all these uncertainties it is probably safe to conclude that the Water Loss is of the same order as that determined by transpira-tion experiments. In accordance with this view, Wigglesworth and Gillett (1936) found that a living Rhodnius nymph, which was not excreting, lost water at a rate of 0.12% of its initial weight per hour at 24°C in dry air over sulfuric acid. Assuming an RH of 10% in the air (Beament, 1958), this rate corresponds to a loss of 0.96% of its initial weight per day at 60% RH and 20°C, and may be compared with the value of 0.24% calculated from the transpiration rate (Table XI). The replacement of water lost by transpiration and excretion may now be considered. In pupae and in certain insect eggs from dry habitats, re-placement cannot be accomplished, and they probably rely solely on the impermeability of the surface for the retention of sufficient water for nor-mal development. Acquisition of water may take place by drinking, though in many cases this is restricted to adults and the larvae rely on the intake of water in their food (Leclercq, 1946). Water may also be gained by (a) the retention of metabolic water in forms living on dry diets (Ed-ney, 1957; Wigglesworth, 1965) ; (b) the absorption of liquid water through the cuticle (Ramsay, 1935; Wigglesworth, 1965) ; and (c) the active absorption of water vapor—a process confined to a few species of insects, ticks, and mites (listed by Noble-Nesbitt, 1969, 1970) and often limited to certain stages of the life history. Since the absorption is de-pendent on relative humidity rather than saturation deficiency (Mellan-by, 1932), its control is likely to be complex. The ecological significance of water-vapor absorption is not clear. It generally occurs from high rela-tive humidities (70% or more), and its value may possibly lie in making the insect independent of a supply of liquid water.
eBook - PDFAtmosphere, Ocean and Climate Dynamics
An Introductory Text
- David H. Miller, John Marshall, R. Alan Plumb, J. Van Mieghem(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
* Such systems are not uncommon, being found where the spacing of rains is no more than a few days, in lands of high groundwater, and in artificially irrigated lands, including urban green areas. 274 TRANSPIRATION OF WATER FROM LEAVES 275 In comparison with a water body, a vegetation-soil ecosystem has small heat storage, as good absorption of solar radiation, and a better linkage with the atmosphere by means of convective exchanges because it is rougher. These likenesses and differences suggest a little about the process of evaporation from ecosystems, the energy sources that power it and the external conditions that govern it. TRANSPIRATION OF WATER FROM LEAVES Transpiration plays a role in the operations of vegetation that is somewhat more than just a leakage of water that happens to occur when cells are opened to receive C0 2 from the environment. It represents an energy subsidy (Odum, 1971, p. 43) to the ecosystem from outside. This subsidy powers the intake of nutrients from the soil and thus is a mechanism for nutrient conservation in the soil-vegetation system (Odum, 1971, p. 95). Also, by cooling the leaves it helps to reduce the respiratory heat loss (i.e., the 'disorder pump-out') necessary to maintain the biological structure (Odum, 1971, p. 43). While this book tends to deal more with the circulations of water outside plant tissue in ecosystems—delivery of rain, interception, infiltration, and so on—we cannot forget the important role of water within the tissues of the plants in the system. While transpiration is a part of the functioning of life processes of plants, it is also at the same time a physical process. The usual number of kilojoules of energy are converted to latent heat, drawing on one or another source of energy, when a certain mass of water is vaporized; water has to be delivered to the site where vaporization can take place; and the vapor has to be carried away.
- F I Woodward, J E Sheehy(Authors)
- 2017(Publication Date)
- Butterworth-Heinemann(Publisher)
14 Introduction to the effects of the environment on biological organisms exoskeleton of animals. These resistances may be vari-able; for example, the stomata of plants, sweat pores of humans and spiracles of insects. These variable-resistance pathways allow the organism to exert a large measure of control on water vapour diffusion to the atmosphere. The existence of plants and animals is very dependent on water and large quantities may be lost from the organism to the environment. This water must be re-plenished from a source, or desiccation will occur. The source is the soil for plants and pools or streams for animals. The water potentials of different regions of the plant have been studied extensively and this has enabled a clear picture of water movement and water status in the plant to emerge. There is a gradient of water potentials between the highest in the soil at — 1 x 10 5 Pa (in the typical example shown in Figure 1.5) and the atmos-phere at -1000 x 10 5 Pa. The 'suction' holding water in the soil, which is close to saturation in Figure 1.5a, is mainly due to the matric potential. The lowest water potential of the system is that of the atmosphere and this exerts a suction on the water at a higher water potential, in the plant. The stomatal pores of the leaf are the major escape routes for water from the plant to the atmosphere. This water escape is strictly controlled so that Water Loss from the plant does not exceed supply from the soil. If the loss greatly exceeds the supply then wilting (pressure potential tends to zero) and eventually death occur. The leaf cell is at the lowest water potential in the plant (—12 x 10 5 Pa) owing to the accumulation of osmotically active solutes at an osmotic potential of — 20 x 10 5 Pa. This tends to become more negative during the day through the accumulation of photosynthetically produced carbo-hydrates and to become more positive at night as a result of respiration and carbohydrate utilization.
eBook - PDF- Marie Dunford, J. Doyle, Marie Dunford(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
© paolo gislimberti/Alamy Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 241 7.2 Water Loss, Intake, Balance, and Imbalance is colder and drier, as more water vapor needs to be added to the inspired air. Increased levels of ventila- tion as a result of exercise may also cause an increased insensible loss of water. Skin must be kept moist to prevent drying and cracking, and some of the water that diffuses into the skin is lost from the body. Water Loss by this mecha- nism may also increase in dry environments with low humidity. Total insensible Water Losses average approx- imately 1,000 milliliters (mL) or ∼36 oz (∼4.5 cups) per day for the average person. The three major areas of sensible Water Loss are the fluid lost in feces, urine, and sweat (Figure 7.7). The amount of water in feces is variable, but loss by this route averages approximately 100 mL (∼3.5 oz) per day. This is not typically a major avenue of Water Loss by the body, unless an individual has a disease such as dysen- tery that results in large volumes of watery diarrhea. The renal system provides the major physiological mechanism for controlling fluid balance in the body via the production and excretion of urine. Urine output can vary dramatically, but for the average person under homeostatic conditions, it is approximately 1,500 mL per day (∼54 oz, or 6 to 7 cups). The amount of renal Water Loss is highly variable and can be influenced by the amount of fluid and salt intake, renal function, the action of various hormones, and the consumption of compounds that have a diuretic effect.
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