Ratios can be simplified. In the school example, there were 20 teachers to 500 pupils. If we divided the children up into equally sized classes, then each of the 20 teachers' classes would have 25 pupils. That means that for each teacher there are 25 pupils, or alternatively, the teacher-to-pupil ratio is 1:25. Another way to work this out is to divide both sides of the ratio 20:500 by 20. Note that 20:500 is the same as 1:25. Just like there are different ways of writing a fraction (for example ), there are different ways of writing one ratio.
Fraction
In common usage a fraction is any part of a unit.
Fraction may also mean:
Proportionality
A proportionality relationship happens when two quantities or numbers "x" and "y" are related multiplicatively by a fixed number. This can occur when either their ratio "x"/"y" is a fixed number (direct proportionality), or their product "xy" is a fixed number (inverse proportionality). If "x" is directly proportional to "y", then we write formula_1. The fixed number of a proportionality relationship is called the constant of proportionality.
Mitochondria
Mitochondria (sing. mitochondrion) are organelles, or parts of a eukaryote cell. They are in the cytoplasm, not the nucleus.
They make most of the cell's supply of adenosine triphosphate (ATP), a molecule that cells use as a source of energy. Their main job is to convert energy. They oxidise glucose to provide energy for the cell. The process makes ATP, and is called cellular respiration. This means mitochondria are known as "the powerhouse of the cell".
In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signalling, cellular differentiation, cell death, as well as the control of the cell division cycle and cell growth.
A mitochondrion contains two membranes. These are made of phospholipid double layers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct compartments within the mitochondrion. They are:
The mitochondria's main role in the cell is to take glucose and use the energy they stored in its chemical bonds to make ATP in a process called cellular respiration. There are 3 main steps to this process: glycolysis, the citric acid cycle or Krebs cycle, and ATP Synthesis. This ATP is released from the mitochondrion, and broken down by the other organelles of the cell to power their own functions.
It is thought that mitochondria were once independent bacteria, and became part of the eukaryotic cells by being engulfed, a process called endosymbiosis.
Most of a cell's DNA is in the cell nucleus, but the mitochondrion has its own independent genome. Also, its DNA shows substantial similarity to bacterial genomes.
The shorthand for mitochondrial DNA is "either" mDNA or mtDNA. Both have been used by researchers.
Mitochondria divide by binary fission similar to bacterial cell division. In single-celled eukaryotes, division of mitochondria is linked to cell division. This division must be controlled so that each daughter cell receives at least one mitochondrion. In other eukaryotes (in humans for example), mitochondria may replicate their DNA and divide in response to the energy needs of the cell, rather than in phase with the cell cycle.
An individual's mitochondrial genes are not inherited by the same mechanism as nuclear genes. The mitochondria, and therefore the mitochondrial DNA, usually comes from the egg only. The sperm's mitochondria enter the egg, but are marked for later destruction. The egg cell contains relatively few mitochondria, but it is these mitochondria that survive and divide to populate the cells of the adult organism. Mitochondria are, therefore, in most cases inherited down the female line, known as "maternal inheritance". This mode is true for all animals, and most other organisms. However, mitochondria is inherited "paternally" in some conifers, though not in pines or yews.
A single mitochondrion can contain 2–10 copies of its DNA. For this reason, mitochondrial DNA is thought to reproduce by binary fission, so producing exact copies. However, there is some evidence that animal mitochondria can undergo recombination. If recombination does not occur, the whole mitochondrial DNA sequence represents a single haploid genome, which makes it useful for studying the evolutionary history of populations.
The near-absence of recombination in mitochondrial DNA makes it useful for population genetics and evolutionary biology. If all the mitochondrial DNA is inherited as a single haploid unit, the relationships between mitochondrial DNA from different individuals can be seen as a gene tree. Patterns in these gene trees can be used to infer the evolutionary history of populations. The classic example of this is where the molecular clock can be used to give a date for the so-called mitochondrial Eve. This is often interpreted as strong support for the spread of modern humans out of Africa. Another human example is the sequencing of mitochondrial DNA from Neanderthal bones. The relatively large evolutionary distance between the mitochondrial DNA sequences of Neanderthals and living humans is evidence for a general lack of interbreeding between Neanderthals and anatomically-modern humans.
However, mitochondrial DNA only reflects the history of females in a population. It may not represent the history of the population as a whole. To some extent, paternal genetic sequences from the Y-chromosome can be used. In a broader sense, only studies that also include nuclear DNA can provide a comprehensive evolutionary history of a population.
Menominee, Michigan
Menominee is a city in the U.S. state of Michigan. Around 13000 people live in Menominee. It is part of the twin-city area with Marinette, Wisconsin. It is on the north bank of the Menominee River where the river empties into Lake Michigan. Marinette, Wisconsin is on the south bank of the river.
Mortar and pestle
A mortar and pestle are two tools used with each other to mill (grind) and mix substances.
The "Mortar" is bowl-shaped, and used to hold the substance to be ground. Mortars have smooth, rounded bottoms and wide mouths. The "Pestle" is a stick used for pounding and grinding.
Mortars and pestles are sometimes used in pharmacies to crush various ingredients to make drugs. They can also be used in cooking to grind herbs.
Mortar
Mortar can refer to different things:
1212
1212 (MCCXII) was .
1192
1192 (MCXCII) was .
Hiram E. McCallum
Hiram E. McCallum (1900 - January 13, 1989) was a mayor of Toronto, Ontario, Canada, from 1948-1951.
Walter Cronkite
Walter Leland Cronkite, Jr. (November 4, 1916 - July 17, 2009) was an American news reporter. He was the anchor of CBS News from 1962 to 1981. Important events he reported included when President John F. Kennedy was assassinated. He reported the Apollo 11 moon landing. He also reported on the Watergate scandal, which led to President Richard Nixon resigning from his position. He was often called "the most trusted man in America." People across the country tuned in nightly to hear his coverage of the Vietnam War as it progressed.
The Walter Cronkite School of Journalism and Mass Communication at Arizona State University is named after Walter Cronkite.
Cronkite was born on November 4, 1916 in St. Joseph, Missouri. He studied at the University of Texas at Austin. In 1935 he left school to work for the Houston Post. He later worked for several midwestern radio stations. In World War II he was a war correspondent for United Press International. After the war he was chief correspondent at the Nuremberg trials. He went to work for CBS News in 1950. In 1962 he helped start the CBS Evening News. He served as the news anchor until he retired in 1981.