For example, in the presence of H < sub > 2 </ sub > O < sub > 2 </ sub > formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular parasites ( such as, for example, the nematode worms involved in filariasis ); and also certain bacteria ( such as tuberculosis bacteria ).

In the presence of a chemical gradient bacteria will chemotax, or direct their overall motion based on the gradient.

Commonly, this term is used to refer specifically to infectious diseases, which are clinically evident diseases that result from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular organisms, and aberrant proteins known as prions.

An infection that does not and will not produce clinically evident impairment of normal functioning, such as the presence of the normal bacteria and yeasts in the gut, is not considered a disease ; by contrast, an infection that is asymptomatic during its incubation period, but expected to produce symptoms later, is usually considered a disease.

Interferons ( IFNs ) are proteins made and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites or tumor cells.

For example, a food sample might be analyzed on three different nutrient mediums designed to indicate the presence of " total " bacteria ( conditions where many, but not all, bacteria grow ), molds ( conditions where the growth of bacteria is prevented by, e. g., antibiotics ) and coliform bacteria ( these indicate a sewage contamination ).

Many bacteria cease production of the enzyme in the presence of oxygen.

The protein content of peroxisomes varies across species, but the presence of proteins common to many species has been used to suggest an endosymbiotic origin ; that is, peroxisomes evolved from bacteria that invaded larger cells as parasites, and very gradually evolved a symbiotic relationship.

In January 2006, researchers from the University of Athens analyzed teeth recovered from a mass grave underneath the city, and confirmed the presence of bacteria responsible for typhoid.

The presence of 20S proteasomes in bacteria may result from lateral gene transfer, while the diversification of subunits among eukaryotes is ascribed to multiple gene duplication events.

Thus, presence of high levels of peptidoglycan is the primary determinant of the characterisation of bacteria as gram-positive.

In 1880, the presence of Rhizobium bacteria in the roots of legumes and their use of catalysts explained the increase of nitrogen in soils so cultivated.

In some arthropods, sex is determined by infection, as when bacteria of the genus Wolbachia alter their sexuality ; some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia.

The ability to transform daidzein into S-equol is based on the presence of certain intestinal bacteria.

The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing debate among researchers in the field.

The medical industry also uses the blood of horseshoe crabs as a test for the presence of contaminant bacteria.

The presence of bacteria in the colon produces an ‘ organ ’ of intense, mainly reductive, metabolic activity, whereas the liver is oxidative.

Tooth decay is caused by certain types of acid-producing bacteria which cause the most damage in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose.

In the presence of oxygen ( aerobic ), some bacteria may directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing biogenic sulfide corrosion.

According to Gold and the Soviet geologists who originated the abiogenic theory, bacteria feeding on the oil accounts for the presence of biological debris in hydrocarbon fuels, obviating the need to resort to a biogenic theory for the origin of the latter.

It is also affected by the presence of snow, hail and ice and can relate to dew, mist and fog.

Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself.

Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of polar ice caps and glaciers, but there is no evidence of either.

A competing theory to explain the presence of ice on the equatorial continents was that the Earth's axial tilt was quite high, in the vicinity of 60 °, which would place the Earth's land in high " latitudes ", although supporting evidence is scarce.

:* Species cumulonimbus capillatus ( Cb cap ): Thunderclouds with very high tops that have become fibrous due to the presence of ice crystals ( C < sub > L </ sub > 9 ).

However, the presence or absence of land masses at the poles is not sufficient to guarantee glaciations or exclude polar ice caps.

The presence of snow and ice is a well-understood positive feedback mechanism for climate.

The presence of water ice is supported by spectroscopic observations, which have revealed crystalline water ice on the surface of the moon.

When British scientists in Antarctica performed airborne ice-penetrating radar surveys in the early 1970s, they detected unusual radar readings at the site which suggested the presence of a liquid, freshwater lake below the ice.

Because of the persistent presence of the ice sheet, the island is sometimes taken to be part of Antarctica.

On October 7, 2009, the presence of water ice was confirmed on the surface of this asteroid using NASA ’ s Infrared Telescope Facility.

The presence of ice on 24 Themis supports this theory.

An alternative mechanism to explain the presence of water ice on 24 Themis is similar to the hypothesized formation of water on the surface of the Moon by solar wind.

However, images from Cassini indicate that Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some thick.

Most ice sensors are simple thermal switches, and do not directly sense the presence or absence of ice buildup.

The presence of subfossil bones at Conkling Cave and Shelter Cave in southern New Mexico show that the species was present south of its current range at the end of the last ice age, leading some experts to project that the species could become increasingly vulnerable as global climate change increases the humidity in semiarid regions.

In 1974, when British scientists in Antarctica performed an airborne ice-penetrating radar survey and detected strange radar readings at the site, the presence of a liquid, freshwater lake below the ice did not instantly spring to mind.

There, they are one of the best lines of evidence for the recent presence of liquid water on Mars in the recent geological past, probably resulting from the slight melting of snowpacks on the surface or ice in the shallow subsurface on the warmest days of the Martian year.

Quaoar — a trans-Neptunian object of similar size — has strong water ice absorption features in its spectra but also has a very red color in the visible implying the presence of the ultrared matter on its surface.

The presence of crystalline water ice, and possibly ammonia ice may indicate that a renewal mechanism was active in the past on the surface of Orcus.

Glacial striation and the presence of chalk and flint erratics that originated from the bed of the North Sea demonstrate the influence of ice action on the geomorphology of the islands.

For example, the chemical composition of and the presence of volcanic ash with the specific acidity spikes in the Greenland ice cores presents clear evidence that they are volcanic, not impact, in origin.