Excretion
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What is excretion in biology?
Excretion is how animals get rid of waste and nitrogen-based byproducts from metabolism. It's how organisms manage osmotic pressure, which is the balance of ions and water, and keep the right acid-base levels. This process helps maintain homeostasis, keeping the organism's internal environment stable.
The kidneys are key to the excretory system in mammals. They eliminate waste and extra substances from the blood, which then exit the body as urine.
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Why do living things need to excrete waste?
Living things need to excrete waste to maintain health and sustain life. Excretion is how organisms control osmotic pressure and maintain acid-base balance, promoting homeostasis (the constancy of the organismās internal environment).
Waste products and poisonous substances, produced by metabolic activities, must be removed or detoxified to preserve the health of the organism. If waste disposal mechanisms are blocked, vital functions can be destroyed. Some metabolic by-products are toxic and must be removed from living cells as quickly as they are produced to ensure the normal progression of vital chemical events.
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Which organs are part of the human excretory system?
The human excretory system, also known as the urinary system, is responsible for eliminating waste and excess substances from the body. The primary organs of this system include the kidneys, which produce urine, and the ureters, which transport urine to the bladder. The bladder stores urine until it is eliminated through the urethra.
The lungs also function as excretory organs, removing carbon dioxide and other gases from the blood. Additionally, the liver eliminates waste products via bile, and the skin excretes waste through sweat, though to a minor extent.
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How do the kidneys help remove waste from the body?
The kidneys filter waste and excess substances from the blood to produce urine. Each kidney contains about 1 million nephrons, which are the functional units responsible for urine production.
During this process, blood pressure forces water and salts through capillaries in the glomerulus into the nephron. Most water and essential substances are reabsorbed back into the blood, while the remaining filtrate becomes urine. The kidneys also secrete substances like renin, erythropoietin, and vitamin D. By selectively reabsorbing water and secreting specific substances, the kidneys maintain a stable internal environment by regulating water content, osmotic pressure, and acid-base balance. Waste products of protein metabolism, such as urea and uric acid, are retained in the blood if the kidney cannot function normally.
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How do plants get rid of their waste products?
Plants lack specialized excretory systems. They get rid of waste products in the following ways:
* Gaseous Waste Green plants release oxygen through stomata and cell walls during photosynthesis and carbon dioxide during respiration.
* Water Removal Excess water is eliminated through transpiration and guttation.
* Exudation Plants exude substances like resins and latex through hydrostatic pressures and absorptive forces.
* Storage Vacuoles store waste materials, preventing self-toxicity.
* Air Purification Houseplants can absorb airborne pollutants, which are then detoxified by microbes in the plant's roots.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does excretion differ between animals and plants?
Excretion differs significantly between animals and plants. Animals possess specialized excretory systems, such as kidneys, to eliminate nitrogenous by-products like urea, uric acid, or ammonia, which are produced during metabolic activities. In contrast, plants lack such dedicated systems. They eliminate excess water through guttation and transpiration, while gaseous wastes like oxygen and carbon dioxide are released via stomata and cell walls. Plants may also secrete substances like resins and saps.
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Excretion, the process by which animals rid themselves of waste products and of the nitrogenous by-products of metabolism. Through excretion organisms control osmotic pressureāthe balance between inorganic ions and waterāand maintain acid-base balance. The process thus promotes homeostasis, the constancy of the organismās internal environment.
Every organism, from the smallest protist to the largest mammal, must rid itself of the potentially harmful by-products of its own vital activities. This process in living things is called elimination, which may be considered to encompass all of the various mechanisms and processes by which life forms dispose of or throw off waste products, toxic substances, and dead portions of the organism. The nature of the process and of the specialized structures developed for waste disposal vary greatly with the size and complexity of the organism.
Four terms are commonly associated with waste-disposal processes and are often used interchangeably, though not always correctly: excretion, secretion, egestion, and elimination.
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Excretion is a general term referring to the separation and throwing off of waste materials or toxic substances from the cells and tissues of a plant or animal.
The separation, elaboration, and elimination of certain products arising from cellular functions in multicellular organisms is called secretion. Though these substances may be a waste product of the cell producing them, they are frequently useful to other cells of the organism. Examples of secretions are the digestive enzymes produced by intestinal and pancreatic tissue cells of vertebrate animals, the hormones synthesized by specialized glandular cells of plants and animals, and sweat secreted by glandular cells in the skins of some mammals. Secretion implies that the chemical compounds being secreted were synthesized by specialized cells and that they are of functional value to the organism. The disposal of common waste products should not, therefore, be considered to be of a secretory nature.
Egestion is the act of excreting unusable or undigested material from a cell, as in the case of single-celled organisms, or from the digestive tract of multicellular animals.
As defined above, elimination broadly defines the mechanisms of waste disposal by living systems at all levels of complexity. The term may be used interchangeably with excretion.
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Elimination
Biological significance of elimination
Waste disposal by unicellular and multicellular organisms is vital to their health and to the continuance of life. Animals must take in (ingest) energy-containing chemical compounds, extract a portion of the energy to power their life processes, and dispose of the unusable material or by-products formed during the energy-extraction process. An analogous series of events occurs in an internal-combustion engine. Fuel, containing energy, is taken into the engine, where it is burned, and a portion of the energy released is used to move the pistons. As in living cells, a portion of the energy-containing material (fuel) not utilized in the engine is exhausted in the form of carbon monoxide, carbon dioxide, and other by-products of combustion. Blockage of the exhaust system in an engine results in loss of efficiency and eventual total breakdown. Similarly, the rate of waste disposal in biological systems can and does provide a means of controlling the metabolic rate. Complete blockage of waste-disposal mechanisms in living systems is as effective in destroying vital functions as the cutting off of food, oxygen, or water from the system. In addition, some substances produced as metabolic by-products are toxic in themselves and must be removed from living cells at a rate equal to that at which they are produced by those cells. Thus, the excretion of waste products from living cells must occur continually in order to ensure the normal progression of vital chemical events.
Waste and poisonous substances produced by the metabolic activities of plant and animal communities must, in a similar manner, be removed or detoxified if community health is to be preserved. Collective wastes of individual organisms constituting a community, if allowed to accumulate to any marked degree, will eventually destroy the lives of all the community members.
The biosphere, composed of all individuals and communities of life forms and their environments on the Earth, is equally sensitive to the effects of waste and poison accumulation. A continual buildup of substances harmful to life forms can only result in the eventual destruction of most or all of the presently existing species of plants and animals. Humans are unique among living things in that their activities result in the production of waste materials (pollutants) that, by virtue of their chemical structure, are poisonous to all living things, including themselves. (For information about waste disposal in the biosphere, see biosphere and conservation.)