Task 25 A)
The brain is clearly the most complex biological system 0 scientists can study.
There are 50 billion cells, 0 trillions of connections among these cells, several
"neurotransmitters" (0 small molecules that transmit messages among 0 nerve
cells), and 0 genetic and hormonal controls for the entire system. Tackling this
is more than a lifetime occupation; it's the work of 0 many lifetimes, observes
Stanley Watson, a senior neuroscientist at the University of Michigan. He suggests
that 0 science is likely to need another 200 or 300 years to completely understand
how the brain functions.
Watson recalls that one of the early analogies used to describe the brain was
that of a_telephone switching center. In this view, the brain was the central receiver
and distributor of 0 messages from and to other parts of the body. Data came in
from the senses or an organ, the brain "processed" this information, and a
response or instruction was sent to 0 appropriate sites throughout the body.
"But we now know that it's probably a mistake to think of a molecule doing
a single job," of matching 0 single neurons or neurotransmitter molecules to 0
individual tasks conducted by the brain or nervous system, says Watson. Each 0
nerve cell is more powerful than a single telephone line or switch, able to send
and receive 0 multiple "messages" all at the same time.
B)
Throughout history, 0 food has been used as a symbol of 0 wealth or 0 gratitude,
or to demonstrate 0 position and 0 power. In some cultures, eating 0 lavish and
exotic meals is a sign of 0.wealth and 0 power, whereas eating only the basic
foods is a sign of belonging to a more common class. In some cultures, the offer
of a glass of 0 cool clean water is the greatest compliment or honor one can
receive. In some cultures, whenever you receive a guest, whether for 0 pleasure
or 0 business, you must offer them something to eat or drink: the more lavish the
offering signifies the amount of 0 respect or honor you give that person. Diet is
not a consideration.
In the movie Indiana Johns and the Temple of Doom, there are 0 two scenes
in which the two lead characters are offered meals from a different culture. One
meal, meant to break the ice, consisted of 0 insects. The second meal was
a lavish banquet that featured such delicacies as 0 roasted beetles, 0 live snakes,
0 eyeball soup, and 0 chilled monkey brains for 0 dessert.
C)
At the height of the Ice Age, between 34,000 and 30,000 B.C., much of the
world's water was contained in vast continental ice sheets. As a result, the Bering
Sea was hundreds of meters below its current level, and a land bridge, known as
0 Beringia, emerged between 0 Asia and 0 North America. At its peak, 0 Beringia
is thought to have been some 1,500 kilometers wide. A moist and treeless tundra,
it was covered with grasses and plant life, attracting the large animals that early
humans hunted for their survival.
The first people to reach 0 North America almost certainly did so without
knowing they had crossed into a new continent. Once in 0 Alaska, it would take
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