User talk:Yasser Mostafa Jeibrel

caving
From the comfort of your keyboard, browse the wonders of the underground! As a caver and photographer for over 35 years, I've shot photos in caves all over the world. This site tells the story of caves in words and pictures: what's in them and how it got there. Because caves are so diverse, I've split them into four underground realms. Grab three sources of light, a helmet, some sturdy boots, and your mouse, and have fun exploring - there's LOTS to see! Please treat all caves with respect as these fragile formations are easily damaged. Our motto is: "cave softly and leave no trace of your visit."

nitrogen fixation
Nitrogen is the most abundant element in our atmosphere. It is a vital element as many classes of compounds essential to living systems are nitrogen-containing compounds. Nitrogen is a primary nutrient for all green plants, but it must be modified before it can be readily utilized by most living systems. Nitrogen fixation is one process by which molecular nitrogen is reduced to form ammonia. This complex process is carried out by nitrogen-fixing bacteria present in the soil. Although nitrogen-fixation involves a number of oxidation-reduction reactions that occur sequentially, that reaction which describes its reduction can be written in a simplified way as:

N2 +  6 e-  +  8H+   --->  2 NH4+  (ammonium ion) The ammonium ion (the conjugate acid of ammonia, NH3 ) that is produced by this reaction is the form of nitrogen that is used by living systems in the synthesis of many bio-organic compounds.

Another way by which ammonia may be formed is by the process called nitrification. In this process compounds called nitrates and nitrites, released by decaying organic matter are converted to ammonium ions by nitrifying bacteria present in the soil. The process carried out by these bacteria is also a complex series of oxidation-reduction reactions. The reduction reactions involving nitrate and nitrite ions can be simplified as:

NO3-    +  2e-  +  2H+  --->   NO2-        +  H2O (nitrate ion)                         (nitrite ion) NO2-    +  6e-  +  2H+  -->    NH4+        +  2 H2O Another way in which molecular nitrogen is modified is via the discharge of lightning. The tremendous energy released by the electrical discharges in our atmosphere breaks the rather strong bonds between nitrogen atoms, causing them to react with oxygen. Note in this process, nitrogen is oxidized and oxygen is reduced.

lightning N2 +  O2   -->   2 NO (nitric oxide) The nitrous oxide formed combines with oxygen to form nitrogen dioxide.

2 NO +  O2   --->  2NO2 Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids;

2 NO2 +  H2O  --->  HNO3  +  HNO2 These acids readily release the hydrogen forming nitrate and nitrite ions which can be readily utilized by plants and micro-organisms.

HNO3  >   H+  +  NO3-  (nitrate ions) HNO2  >   H+  +  NO2-  (nitrite ions) Denitrifying bacteria, act on ammonia as well as nitrates produced by death and decay, recycling these compounds as free nitrogen (N2). The nitrogen that is fixed by the processes described above is eventually returned to the atmosphere by this denitrification process, to complete what is commonly referred to as the "nitrogen cycle".

fungi
How are cheese, bread , and soy sauce related to fungi ? A fungus can help make each of these foods. {Ex. Of fungi} -Threadlike fungi -Sac fungi -Club fungi -Imperfect fungi

threadlike fungi
Threadlike fungi are mostly decomposers. They reproduce using spores that are stored in sacs at the end of long threads. The sacs explode and the spores shoot out. A few types of threadlike fungi are parasites.

Threadlike fungi are mostly decomposers. They reproduce using spores that are stored in sacs at the end of long threads. The sacs explode and the spores shoot out. The spores can stay dormant for a long time before growing when the conditions are right. A few types of threadlike fungi are parasites.

Sac fungi
The Ascomycota,formerly known as the Ascomycetae, or Ascomycetes, are a Division of Fungi, whose members are commonly known as the Sac Fungi, which produce spores in a distinctive type of microscopic sporangium called an ascus. Examples of sac fungi are yeasts, morels, truffles, and Penicillium. The majority of plant-pathogenic fungi belong to this group, or the Deuteromycota. Species of ascomycetes are also popular in the laboratory. Sordaria fimicola, Neurospora crassa and several species of yeasts are used in many genetics and cell biology experiments.

club fungi
Most but by no means all of the most interesting fungi we find in our neighborhoods are club fungi. As the drawing at the right indicates, the name "club fungi" derives from the fact that in this group spores, more technically known as basidiospores, are produced on microscopic, club-like structures called basidia (singular basidium). In fact, in technical texts this group is usually referred to as the Basidiomycetes or Basidiomycota.. Basidia cover part of the fungus's reproductive structures. In gilled mushrooms (one is illustrated below), the gills are covered with them. The above diagram shows a cross section of such a gill. Basidospores detach from the basidia and drift down out of the gills, and then are dispersed on wind currents. Basidia occur elsewhere on the fruiting bodies of non-gilled fungi.

Imperfect fungi
Most of the so-called imperfect fungi, a group also called deuteromycetes, are those in whi ch the   s e xua l   r eproduc t i v e   s t age s have not been observed. Most of these appear to be related to ascomycetes although some  have   clear   affinities   to   the   other phyla. The group of fungi from which a particular nonsexual strain has been derived usually can be determined by the features of its hyphae and asexual reproduction. It cannot, however, be classified by the standards of that group because the classification  systems   are   based   on   the   features related to sexual reproduction. One consequence  of   this   system   is   that   as   sexual reproduction is discovered in an imperfect fungus, it may have two names assigned to different stages of its life cycle. There are some 17,000 described species of imperfect fungi (figure 36.12). Even though sexual reproduction is absent among imperfect fungi, a certain amount of genetic recombination occurs. This becomes possible when hyphae of different genetic types fuse, as sometimes happens spontaneously. Within the heterokaryotic hyphae that arise from such fusion, a special kind of genetic recombination called parasexuality may occur. In parasexuality, genetically distinct nuclei within a common hypha exchange portions of chromosomes. Recombination of this sort also occurs in other groups of fungi and seems to be responsible for some of the new pathogenic strains of wheat rust.