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In chemistry, a zwitterion, formerly called a dipolar ion, is a molecule with two or more functional groups, of which at least one has a positive and one has a negative electrical charge and the net charge of the entire molecule is zero. Because they contain at least one positive and one negative charge, zwitterions …

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Homeostasis is the state of steady internal conditions maintained by living things. Maintaining homeostasis requires that the body continuously monitor its internal conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular set point. A set point is the physiological value around which the normal range fluctuates. A normal …

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A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells. A …

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Celestial latitude and longitude

The celestial latitude is the angular distance on the celestial sphere measured north or south of the ecliptic along the great circle passing through the poles of the ecliptic and the celestial object. The celestial longitude is the angular distance along the ecliptic from the vernal equinox eastward.

Celestial meridian

The celestial meridian is the great circle on the celestial sphere that passes through the celestial poles and the zenith of the observer.

Celestial equator

The celestial equator is the great circle on the celestial sphere that divides the northern and southern hemispheres and serves as the zero-mark for declination; it is the projection into space of Earth’s equatorial plane.

Celestial poles

The celestial poles are the two points where an extension of Earth’s axis intersects the celestial sphere and about which the celestial sphere appears to rotate daily. As a result of precession, the celestial poles complete a circle around the ecliptic poles every 25,800 years.

Celestial sphere

The celestial sphere is the apparent sphere of the sky; a sphere of large radius centered on the observer; directions of objects in the sky can be denoted by their position on the celestial sphere. See also Celestial axis Celestial meridian Celestial equator Celestial poles Celestial latitude and longitude


Biogas is a mixture of different gases produced by anaerobic decomposition (with methanogen or anaerobic organisms), or fermentation, of biomass – organic material (including animal dung, human sewage, food waste, crop residues, and industrial and municipal wastes). Biogas is a renewable energy source. It is composed primarily of methane (up to 60%), which is the combustible component, carbon …

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