E2science

The living things that drift along in the currents of air.

The air above your head? It's not devoid of life. But the life that's there is nearly invisible. At one end of the scale, bacteria and viruses drift in the breeze. Slightly larger are spores and pollen. Clouds play host to algae, fungi, and bacteria (there are a few species endemic to the stratosphere)-- and why not have an ecosystem in a cloud?--there's water up there. Various seeds have adapted to be spread by wind. And there are numerous inverterbrates, from spiders to caterpillars to wingless mites, who put themselves at the mercy of wind and air to move (in search of food or sex). Spiders can use their silk to balloon (they've been found at altitudes of seven miles, and scientists have evidence that remote islands in the Pacific Ocean, such as Hawaii, were colonized by spiders who ballooned their way there). And though some insects have wings, some are so lightweight that updrafts (even that from a warm stone) can be powerful enough to lift them beyond the biological boundary layer, the zone where their wing speed can exceed the wind speed. So it is that airplanes can find termites and aphids at high altitudes, and that alpine ecosystems can have predators (birds and insects) who prey on the aerial plankton brought back down to the surface by the downdrafts provided by ice and snow.

 

Sources:

Robert R. Dunn. "A head in the clouds: do the microorganisms that circulate in the atmosphere get there by chance or by contrivance?" Natural History. July-August 2009. FindArticles.com. http://findarticles.com/p/articles/mi_m1134/is_6_118/ai_n32339705/ (November 15, 2010)

Robert Krulwich, "Look Up! The Billion-Bug Highway You Can't See," Morning Edition. July 15, 2010. http://www.npr.org/templates/story/story.php?storyId=128389587 (November 15, 2010)

David Lukas. "Of Aerial Plankton and Aeolian Zones." Writing on Air. David Rothenberg, Wandee J. Pryor, eds. MIT Press, 2003. http://books.google.com/books?id=4DeX7Gb-LJ4C&lpg=PA39&ots=InqKd4d1F_&dq=aerial%20plankton&pg=PA39#v=onepage&q=aerial%20plankton&f=false (November 15, 2010)

Most of us have seen, through a microscope, amoebas, those tiny, one-cells that flow about, changing shape. But did you know you have a number of them inside your body?

There are several species of amoeba which are commensal or symbiotic with us. This article will not deal with the numerous species whose main business is to cause human disease. These are the harmless folks. (Usually.) This is by no means a complete list! There are a lot of these guys!

• The mouth amoeba, Entamoeba gingivalis, lives in your mouth, and is passed directly from person to person in kissing and in sharing food. It does not form cysts as most human amoebas do. Nearly everyone has them. They feed on loose cells and debris in the mouth.
• The intestinal amoeba, Entamoeba coli, lives in the large intestine, but lives only on the food there, not on your own cells. It sometimes eats parasites like Giardia, thus doing you a favor. This one will encyst, pass out of your intestine, and wait for someone else to eat food contaminated with human waste, or drink contaminated water. The cyst can survive the acid in the stomach, so that the amoeba ends up where it wants to be in this next person. Unlike many organisms which follow this route, though, it will do you no harm.
• The dysentery amoeba, Entamoeba histolytica, is a shifty fellow, though. Most of the time it's perfectly harmless, and about 10% of the human population carries it around all the time, but under the right circumstances - usually some weakness in the immune system, but there may be other reasons - it can cause serious or fatal illness by invading the intestinal wall and ingesting host tissues. It may also spread to the liver and other organs. It too, like Entamoeba coli, is transmitted in encysted form with contaminated food or water.

Kingdom Protista, Sarcondines.
Authorities differ very much in the classification of Protista, some ranking them in classes, some in numerous phyla. Since amoebas do not "breed", but rather reproduce by fission, the concept of species is a difficult one to apply in their case anyway.

In chemistry, "turnover" refers to the ability of a catalyst to, for lack of a better term, "turn over" after releasing a product molecule. Turnover leads to the regeneration of the "naked" catalyst, which can bind another molecule of starting material and restart the catalytic cycle.

All catalytic cycles operate on the same basic principle: a substrate (or multiple substrates) binds to the catalyst in some way, a chemical transformation of the substrate(s) takes place, and product is released with regeneration of the starting catalyst. A catalytic cycle is analogous to a conveyor belt: substrate goes on the conveyor belt, gets moved to a different position in "chemical space," and is released as the conveyor belt "turns over." Turnover is necessary in order for a process to be catalytic, and achieving catalyst turnover is often the most difficult part of turning a linear reaction into a catalytic cycle. One glaring problem is that the binding affinity of the product for the catalyst must be less than the binding affinity of the substrate for the catalyst. Otherwise, each molecule of catalyst would perform the catalytic cycle only once, then get stuck in the product-bound state. Such a system is missing turnover, and is stoichiometric rather than catalytic. The conveyor belt gets jammed up, in a sense.

Generalizing on this idea, we can say that in order to achieve turnover and avoid logjam, none of the active catalyst species should be too stable. For transition-metal catalysts this is rarely an issue, because transition metals can access a variety of oxidation states (i.e., possess a widely varying number of bonds) and easily bind and release organic molecules. Main-group catalysts are a different story. The common "organic atoms" (C, N, O, H, and the halogens) have oxidation states of widely varying energies, so falling into an unreactive thermodynamic sink along any reaction pathway involving these guys is likely. This problem is often circumvented by the inclusion of a reactive compound in stoichiometric quantities that "kicks up" the catalyst into its most reactive form. Iodine(III), for example, can catalyze C-O bond formation next to a carbonyl group...but to do so requires one full equivalent of mCPBA, in order to reoxidize iodine(I) back to iodine(III) and turn over the catalyst. Without the oxidant, iodine(I) forms upon release of the product and it gets stuck there. A full equivalent of oxidant is required because the catalyst must be reoxidized each time it runs the cycle.

Each run of the catalytic cycle is called a turnover. The number of times each molecule of a catalyst can perform the catalytic cycle before decomposition is called turnover number (TON). Higher TONs are good because they correspond to smaller catalyst loadings, the amount of catalyst required to transform a given amount of substrate. The number of turnovers a catalyst performs in a given time unit is called the turnover frequency (TOF). Higher TOFs are again good because they mean shorter reaction times. The turnover-limiting step of a cycle is the step with the slowest rate constant, which limits how often molecules of the catalyst turn over. You'll often hear people judge the quality of a catalytic cycle by these parameters.

Turnover in biochemistry refers to the idea that organisms reuse and recycle their components continually. Everything is being regenerated in a cyclical process, degraded and resynthesized. Though the equilibrium remains fairly constant, the organism is nowhere near static. For example, in the average human body every single cell will have been replaced with a new one within seven years.

Turnover can speed up or slow down depending on environmental factors. Turnover will grind to a halt in bacteria if they are exposed to extreme cold temperatures, such as a collection hurtling through space or trapped deep beneath ice. As soon as the surroundings change: food becomes abundant or circumstances allow the initiation of biological processes again, turnover will reinitiate. Like a river, no organism remains exactly the same forever. Change is inherent in all composite things.

Turnover is especially important to metabolism, since a degraded part of a pathway must be replaced to ensure the stable continuation of chemical reactions.

The highly diverse genus, brassica includes the vegetable we know as cabbage. Depending on your first cabbage experience, you will either love or hate this vegetable. Unfortunately, cabbage has been much maligned by improper handling and poor cooking. Don't let these culinary crimes put you off this noble and versatile vegetable - better yet, let's find out how to treat cabbage with the respect it deserves.

Apart from the familiar varieties of heading cabbage, there are also dozens of non-heading; leaf, stem and flower based cabbages from around the world, each with its own unique place in divergent cuisines and their methods of preparation.

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History

Cabbages are an extremely popular vegetable in Europe, Africa, through Central Asia and right out to Far East Asia. The regular heading cabbage most of us would be familiar with has its parentage with the wild cabbage that is native to coastal areas of the Mediterranean. This plant would have been gathered for countless millennia, but the first record of its domestication dates to around 2500 BC. This vegetable was thought of very highly by the Romans, and was even believed to counter some of the excess to which that society was prone. According to Cato,

"The cabbage surpasses all other vegetables. If, at a banquet, you wish to dine a lot and enjoy your dinner, then eat as much cabbage as you wish...It will make you feel as if you had not eaten, and you can drink as much as you like."

It was most likely the Romans who were responsible for the introduction of wild cabbage to the British Isles.

Sometime later, after centuries of domestication and due to selective selection of forma when planting new crops, cabbages started to form heads. The regular round, white and tightly packed cabbage you see in greengrocers everywhere made its first appearance circa 1100 AD, around the area we know as Germany. Cabbage's Lilliputian cousin, the Brussels sprout was first extensively recorded in 1587, although evidence of this vegetable in Northern Europe pre-dates this by almost 1000 years.

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Chemistry

When cooked, cabbages have a lot going on in the chemistry department. The cabbage group of vegetables has been thoroughly investigated by chemists, and indeed perhaps the first detailed study of what chemically occurs to a cooked vegetable was undertaken with cabbages in 1928.

There are a couple of reasons behind early scientific interest. Firstly, cabbages are a stinky vegetable - there is little avoiding this fact. They give off a range of malodiferous substances as they cook. Secondly, and more ominously, the cabbage family includes mustard and horseradish, both of which contain powerful isothiocyanate compounds that were synthesized during World War I to produce the horrific mustard gas.

Among the aromatic compounds released as cabbage is exposed to heat are hydrogen sulfide (rotten egg gas), ammonia, mercaptans and methyl sulfide. The longer cabbage is cooked, the more prodigious is the resultant gaseous output. Eventually, after a prolonged period of cooking, powerful and unpleasant tri-sulfides will be formed. To make matters worse, aluminium cookware reacts poorly with cabbages. The oxides in the metal interact in an unpleasant manner with the sulfurous material in the vegetable.

Much of this can be avoided by cooking cabbage for brief periods of time and in non-aluminium cookware. For instance, the amount of hydrogen sulfide produced by cabbages doubles from the 5th to 7th minute of cooking. If you need any other reasons to avoid long-boiled cabbage, this is it.

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Varieties

European cabbage

Heading cabbage, which includes the regular white, the crinkly savoy and the vivid red cabbages, as well as tiny Brussels sprouts all belong to one diverse species, Brassica oleracea. All parts of these cabbages are edible, including the coarse white stem running up the middle of the vegetable. Any limp outer-leaves need to be removed and depending on the preparation, will either be shredded, for quickly braised dishes and salads, or in the case of stuffed cabbage, the leaves are removed whole. Owing to Brussels sprouts' small size, they are either left whole, or cut into wedges.

Flowering cabbage includes broccoli and cauliflower, as well as their faddish hybrid progeny, the broccoflower. All parts of these varieties are edible; stems, leaves and inflorescence. In the case of cauliflower, the large leaves are encouraged to grow over the vegetable during growth, thus inhibiting the production of chlorophyll that would taint cauliflower's trademark pale colour. These varieties are generally cut or snapped into individual flowering heads, known as florets, before proceeding with a recipe. The exception is some elaborate European and Indian cauliflower preparations, which require the entire vegetable to be cooked whole.

Stem cabbage is mainly represented by one strikingly presented vegetable, the kohlrabi. This cabbage varies in size from a tennis ball, up to a large grapefruit and usually sports a vivid purple exterior; apart form a pale green variety that is sometimes available. It grows in an intriguing manner - the stem abruptly swells to an alarming width, with the leaf containing branches growing upwards from the swollen stem. Generally, kohlrabi is sold minus the leaves, but they are as well edible. Due to the dense, root vegetable-like texture of kohlrabi, it is normally sliced into smaller wedges before cooking.

Leafy cabbage is an extensive group, which includes the original wild cabbage, kale and the black-leafed Italian cavolo nero. These cabbages do not form heads and thus all of the culinary action is to be found in separate leaves. They should be treated in a manner similar to spinach or silver beet, with their slightly coarser texture dictating perhaps a minute or so more cooking time. Make sure to wash these leafy cabbages well before use.

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Asian cabbage

I have deliberately kept this section separate, as although these cabbages have many similarities to their Euro cousins, their treatment is sufficiently different to warrant stand-alone status.

Chinese cabbage Brassica pekinensis is also known by its Chinese name - won nga buck, as well as Peking cabbage and Napa cabbage. It is loose-headed, with white to pale green leaves and a distinctive elongated shape. They are quite large, with the average sized football making a small specimen. These cabbages are either sliced into small sections for stir-frying or soups, or more often than not - pickled. This is done in either the Chinese manner, finely shredded and subtly spiced - which some food historians believe to be the precursor to sauerkraut; or in the Korean style, kimchi. This addictive and volatile preparation is highly spiced and includes a goodly amount of fiery red chilli.

Chinese broccoli B. alboglabra is also commonly known by its Chinese name, gai larn. This variety has light green, thick stems and coarse, dark green leaves. It is commonly found in stir-fries and soups, as well as the ubiquitous dish found on Chinese menus simply as "Chinese vegetable". This is lightly steamed gai larn dressed with oyster sauce, ginger and stock.

Bok choy B. chinensis is also sometimes sold as Shanghai cabbage. It possesses wide, succulent and pale stems with uniform mid-green leaves. This cabbage is once again popular in soups as well as in famous Cantonese dishes such as mermaid's tresses and lion's head meatballs. A variation is rosette bok choy B. chinensis var. rosularis, which has deeper green, round leaves and grows in an attractive and compact rose shape.

Choy sum B. chinensis var. parachinensis is also known as flowering cabbage. It has long, pale and tender stems and mid-green leaves. This variety is often sold with compact yellow flowers, hence its common name.

Mustard cabbage B. juncea is known in Chinese as gai choy. This cabbage has coarse and thick stems, somewhat reminiscent of bok choy and dark, frilly foliage. Mustard cabbage has a pungent, slightly bitter flavour that is prized for use in strongly flavoured soups. This is the cabbage used in the powerful condiment - Szechwan pickled cabbage.