Exercise 6. Fighting Bacteria.

Divide into two groups. Each group should read either Text A or Text B about two unusual methods of fighting bacteria. Then in pairs discuss your text with the partner. Try not to miss any details.

 

Text A. Tea Aids Oral Health

By Sarah Graham

A spot of tea may offer more than just a pleasant way to pass the afternoon. Research findings presented this week at the 103rd General Meeting of the American Society for Microbiology in Washington, D.C. suggests that it can help fight bad breath and may boost the powers of toothpaste.

Christine Wu and Min Zhu of the University of Illinois at Chicago College of Dentistry isolated chemical components of tea leaves known as polyphenols and tested them against three species of bacteria known to cause bad breath. The researchers found that the compounds, specifically catechins and theaflavins, inhibited growth of the oral bacteria over a 48-hour incubation period. What is more, lower concentrations of the chemicals interfered with the enzyme that catalyzes the production of hydrogen sulfide, which has the notorious smell of rotten eggs, and reduced its production by 30 percent. The compounds studied by the scientists are present in both green tea and black tea, although they are more abundant in the latter.

In a second study, researchers reported that green tea may provide additional benefits. Milton Schiffenbauer of Pace University and his colleagues tested tea's ability to fight bacteria that cause infections such as strep throat and dental caries. They found that green tea extracts and polyphenols--particularly those from caffeinated beverages--inhibited bacterial growth. Adding these agents to toothpaste and mouthwash, he notes, may make them more effective at combating microbial agents. (From Scientific American Online, May 21, 2003)

 

Text B. Scientists Explain Why Vegetable Recipes Skimp on Spices

By Kate Wong

Several years ago, a team of researchers from Cornell University proposed that the spices used in traditional meat-based cuisines originally served not as flavor, but to stave off bacteria and fungi. Now new research is providing further food for thought: findings reported in the June issue of Evolution and Human Behavior explain why vegetable-based dishes tend to lack such spiciness.

Plants, it turns out, don't require so much protection against microorganisms as meats because they have their own natural chemical and physical defenses, which continue to function after cooking. Cornell neurobiologist Paul W. Sherman and undergraduate Geoffrey Hash thus predicted that if spices first served as antimicrobials, especially in warmer climates, vegetable recipes in the same countries surveyed for the meat research should feature fewer spices. Subsequent investigation bore this out. Analyzing 2,129 traditional vegetable recipes from 36 different countries, the team found that spice usage was far lower than that found in meat-based dishes from the same cultures. Indeed, of the 41 spices considered, 38 appear more frequently in meat recipes; the three that don't fit this pattern - sesame, caraway and sweet pepper - offer little protection anyway.

"Humans have always been in a co-evolutionary race with parasites and pathogens in foods, and our cookbooks are the written record of that race," Sherman asserts. "We haven't had to 'run' as hard when we ate vegetables. We haven't had to use extra pharmaceuticals to make vegetables safe for consumption." (From Scientific American Online, July 11, 2001)

 

Exercise 7. Speak about bacteria and their role on our planet. Summarize all facts which have been discussed in this unit.

 

Unit 5. Domestic and Domesticated Animals

 

A horse! A horse! My kingdom for a horse!

William Shakespeare

The Tragedy of King Richard the Third

 

I have known the horse in war and in peace, and there is no place where a horse is comfortable. The horse has too many caprices, and he is too much given to initiative. He invents too many ideas. No, I don’t want anything to do with a horse.

Mark Twain

 

Exercise 1. What do you know about domestication of animals?

1. What domestic animals do you know? What wild animals do they come from?

1. What was the first domesticated animal? Why?
2. What purposes were domesticated animals used for?
3. How does the process of domestication take place?

 

Exercise 2. Read the following two texts (Text A and Text B) about domestication of dogs and goats to check your answers in Exercise 1.

 

Text A. The Origin of Dogs

Where did our best friend originate? Researchers are looking to DNA to dig up answers about where, when and why pooches became popular

By Katherine Harmon

From Chihuahua to Great Danes, all domestic dogs (Canis familiaris) seem to be descended from the Eurasian gray wolf (Canis lupis). But what we still don't know is exactly when and where our best friends transformed from predators into partners. And such knowledge might help solve the long-disputed question of exactly why dogs were the first animal to be domesticated.

The dog genome was first decoded in 2005—and even before that researchers had been using genetic tools to track Fido's first home. Early research pointed toward east Asia as the locus of first taming after the discovery of high genetic diversity and other key markers in dog populations from various villages there. Some investigators, however, have since pointed out that the genetic search sampled more east Asian village dogs, neglecting similar pups roaming other villages around the globe. That's where the Village Dog Genetic Diversity Project at Cornell University comes in. Starting with a recent genetic analysis of dogs in African villages, the Cornell group hopes ultimately to create a detailed DNA-based map of canine ancestry worldwide, which in turn should provide a new understanding of the ancient humans who took them in.

One part of that new insight appeared earlier this month in the Proceedings of the National Academy of Sciences (PNAS), in a study that calls into question the assumption of dogs' east Asian origin. A team led by Adam Boyko, a researcher at Cornell's Carlos D. Bustamante Lab, sampled 318 village dogs in Africa (as well as hundreds of dogs from North America and Europe for comparison) and discovered that the high genetic diversity of canines there resembles that found in east Asia. "We found almost without exception they're descended from different ancestral populations," Boyko says of the village dogs sampled in Africa. That means they may have been there just as long as others had been in east Asia.

Researchers have also yet to figure out when people first began raising dogs. The going theory is that dogs were domesticated somewhere between 15,000 and 40,000 years ago. But, Boyko explains, genetic testing has not gone deep enough to come up with a more refined date. To try to track down some more clues, field crews have fanned out around the globe this summer to test village dogs in Vietnam, New Guinea, Malaysia and other locations in Eurasia in order to get more data.

Of course, scrappy village dogs aren't often the focus of heartfelt conservation efforts, and some even face active elimination programs. But these pups also have challenges from newly arrived European-descent dogs, which threaten to make a splash in the regional gene pool. "It is unclear the degree to which older populations will be able to maintain their genetic identity and persist in the face of modernity," Boyko and his co-authors wrote in the PNAS paper. So time is of the essence in digging up a solid answer about doggie descent.

Looking back into the pooch family tree will help researchers learn more not only about dogs, but about ancient people, as well. A genetic map of dog domestication could reveal important information about human migration and trade routes. "We may be able to turn dogs into a genetic marker for what human populations were doing," Boyko says. He adds that he and his colleagues also plan to "look for which regions of the genome went under selection earliest," and from that "we'll also learn what traits were selected for at that time." That knowledge, along with a little help from archaeologists, may be able to uncover sniff out just why the dog was so special and became most likely the first domesticated species. (From Scientific American Online, August 20, 2009)