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Bat Death Mystery Solved





Text 3

Yeasts

Text 2

Retell one of the texts.

Read the texts using your dictionary.

Pair work. Ask and answer 6 questions to the Text 1.

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any of certain economically important single-celled fungi, most of which are in the class Ascomycetes, only a few being Basidiomycetes. Yeasts are found worldwide in soils and on plant surfaces and are especially abundant in sugary mediums such as flower nectar and fruits. There are hundreds of varieties of ascomycetan yeasts; the types commonly used in the production of bread, beer, and wine are selected strains of Saccharomyces cerevisiae . The small cakes and packets of yeast used in food- and beverage-processing contain billions of individual yeast cells, each about 0.075 mm in diameter.

Yeasts reproduce asexually by budding: a small bump protrudes from a parent cell, enlarges, matures, and detaches. A few yeasts reproduce by fission, the parent cell dividing into two equal cells. Some yeasts are mild to dangerous pathogens of humans and other animals (e.g., Candida albicans, Histoplasma, Blastomyces).Torula is a genus of wild yeasts that are imperfect, never forming sexual spores.

In food manufacture, yeast is used to cause fermentation and leavening. The fungi feed on sugars, producing alcohol (ethanol) and carbon dioxide; in beer and wine manufacture the former is the desired product, in baking, the latter. In sparkling wines and beer some of the carbon dioxide is retained in the finished beverage. The alcohol produced in bread making is driven off when the dough is baked. The fermentation of wine is initiated bynaturally occurring yeasts present in the vineyards. One yeast cell can ferment approximately its own weight of glucose per hour.



Yeast is 50 percent protein and is a rich source of vitamins B1, B2,niacin, and folic acid. Brewer's yeast is sometimes eaten as a vitamin supplement.

In commercial production, selected strains of yeast are fed a solution of molasses, mineral salts, and ammonia. When growth ceases, the yeast is separated from the nutrient solution, washed, and packaged. Yeast for baking is sold in compressed cakes containing starch or in a dry granular form mixed with cornmeal.

 

Bats are getting moldy and dying, and scientists have identified the culprit in the deadly mystery.

The killer is a member of a group of cold-loving fungi called Geomyces. This white, powdery-looking fungus coats the muzzles, ears and wings of bats and has meant death for more than 100,000 of the night flyers in the northeastern United States.

Bats covered with the fungus, a sickness now called white-nose syndrome, were first spotted in Howes Cave near Albany, N.Y., during the winter of 2006. At that time, field biologists reported caves that were typically covered with hibernating bats had loads of vacancies, which the scientists assume is because the bats either died or were flitting around in search of food. In one case, a cave floor was littered with dead bats.

Since then, scientists have estimated drastic declines in populations of cave-hibernating bats in Connecticut, Maine, New York and Vermont. In some caves, more than 75 percent of the bats have perished.

The caves where bats hibernate from late October through late April or early May in the northeastern United States could be the perfect spots for fungal growth.

Fungi in general do best in moist environments, and so it's no surprise that the researchers found more infected bats in the most humid caves. In addition, this particular fungus can survive at temperatures between 2 degrees to 15 degrees Celsius, which are typical in caves.

The bats also lower their core body temperatures to match that of the caves, making their bodies perfect hideouts for the fungi. (In addition, bats lower their heart rates from about 1,000 beats per minute to four beats a minute during hibernation.)

But bats have done this for millions of years. They have hibernated in these same caves using the same physiological mechanism, dropping their heart rates down, not eating, dropping their core body temperature down, and they didn't used to get moldy.

Why now? The bats may have ingested some environmental contaminant that is causing them to starve, or pesticides may have wiped out their food source, keeping the bats from fattening up before entering caves for hibernation. Their emaciated bodies would then be susceptible to invasion by the fungus.

Another possibility is that the fungal infestation is irritating the bats' skin. The irritation could cause the bats to wake up more often during hibernation. While hibernating bats typically wake up for short periods every two weeks or so, the fungi could cause more frequent wake-ups. These mid-hibernation arousals are costly as the bat warms up its body and turns on other body processes like its immune system. That means the wake-up could use up critical energy in the form of fat reserves, causing the bats to starve.

 





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