Biology J
What is joint ?
The contact area between two bones. There are many different types of joint, including hinge, ball and socket, universal, sliding, and slightly movable.
Who was Joly, John ?
An Irish geologist (1857–1933) who, in 1899, tried to determine the Earth’s age by calculating how long it would take for the rivers to dump salt into the ocean to reach the present salinity levels. It was based on the assumption that oceans were freshwater when first formed. He estimated 90 million years for the age of the Earth. He was more accurate with dating a geological time period. Working with Sir Ernest Rutherford in Cambridge in 1913, and using the radioactive decay in minerals, he estimated that the beginning of the Devonian period—the time between the Silurian and Carboniferous—was not less than 400 million years ago, an age that is pretty well accepted today. Joly collaborated with Henry Horatio Dixon and was the first to explain how sap rises in plants largely due to evaporation from leaves.
What is joule (J) ?
A unit of work and energy; 1 J = 0.239 cal; 1 cal = 4.184 J. It is defined as being equal to the work done when the point of application of a force of 1 newton (N) moves in the direction of the force, a distance of 1 meter (m).
What is junk DNA (noncoding DNA) ?
Genomic DNA that serves no apparent purpose; stretches of DNA that do not code for genes.
What is Jurassic period ?
The middle period of the Mesozoic era, 213 to 145 million years ago. Age of the dinosaurs. Named after the Jura Mountains between France and Switzerland, where rocks of this age were first studied.
What is juvenile ?
A stage in development prior to adult stage.
What is juvenile hormone ?
A chemical hormone in insects secreted by a pair of endocrine glands, corpora allata, close to the brain. It inhibits metamorphosis and maintains larva or nymph characteristics during development and is responsible for determining the molt type. One of three major insect development hormones. Used as a pesticide, it retards the development of insects.
What is juxtaglomerular apparatus ?
A group of specialized cells or tissue in a kidney nephron that is located near the point where the afferent arteriole meets the distal tubule. It is composed of the macula densa, a specialized group of cells in the distal tubule, and the juxtaglomerular cells, epithelioid cells in the media of the afferent arterioles just as they enter the glomerulus. The juxtaglomerular apparatus supplies blood to the GLOMERULUS, controls the glomerular filtration rate (volume of plasma filtered through the glomerulus per second), blood pressure, and circulating volume through the release of rennin, which activates angiotensin, a family of peptide hormones that control blood pressure and body fluid levels.
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