1. Even though the whale-resembling Basilosaurus ostensibly looked different from Mesonychid, scientists have discovered from fossil records that beneath Basilosaurus's flippers were fingers that are anatomically similar to those of a Mesonychid. Such existence of a vestigial organ (trace of homologous organ in other species) serves as a powerful evidence that an evolution had occurred.
2. E
3. The three organisms exemplify a convergent evolution, a process by which unrelated organisms independantly evolve similar trait(s); in this case, wings. We may assume that the three organisms, despite fundamental differences, were pressured into adapting to similar environments where flying was necessary for survival.
4. Organisms which share a more recent common ancestor are more closely related in terms of their DNA structures; to be more precise, in terms of their genetic sequence. By comparing the DNAs of different organisms in the Common Descent Lab, we can get a glimpse about the so-called 'evolutionary tree', a branching diagram that accounts for the degree of change of a certain specie. Many primates we know including monkeys are in the same evolutionary branch as humans. This means that humans are not direct descents of monkeys, but share a common ancestor with them.
5. Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures, and homology refers to the appearance of such homologous structures among different organisms. For example, the limbs of the four modern vertebrates: turtle, aligator, bird and mammal are homologous structures that consist of same basic bones.
2013년 9월 27일 금요일
2013년 9월 2일 월요일
Day 2 Class Activity
Question: Why do humans sweat while dogs don't?
Answer: Unlike dogs, humans have sweat glands. The sweat secreted by the sweat glands conistently vaporizes on our skin and therefore allows our body to cool down spontaneously--water absorbs certain amount of heat when vaporized (heat of vaporization). The only way dogs can moderate their body temperature is panting. The cool air lowers the temperature of the exposed tongue and consequently moderates the body temperature.
Class 1: An informal, hypothetical lab report of the 'Dancing Milk' experiment
A.
Hypothesis
The drop of dish soap, which is a surfactant, had
caused the food coloring to disperse throughout the surface of the milk.
B.
Procedures
1.
Pour
enough milk into three separate pans.
2.
Add
several drops of food coloring to each pan.
3.
Add a
drop of dish soap to the first pan, a drop of alcohol to the second, and a drop
of sesame oil to the third.
4.
Observe
the changes in each pan.
C.
Expectation
Surfactant molecules like dish soap are usually known
to be amphiphilic, meaning they contain both hydrophilic groups (heads) and
hydrophobic groups (tails). As their names suggest, the hydrophilic group of
the molecules actively interacts with water (in this case, milk) and the
hydrophobic group with oil (food coloring), weakening the surface tension of
the milk (by weakening the intermolecular force, the hydrogen bond, existing
between the milk molecules) and eventually blending the food coloring with it,
a phenomenon ostensibly viewed by the observer as ‘spread’.
The hypothesis that the dispersion of the coloring is
attributable to the amphiphilic property of the dish soap may be verified by
adding alcohol and sesame oil, which are substances that are hydrophilic and
hydrophobic respectively, to two separate pans of milk and comparing the
changes. Since neither of the two are amphiphilic, it is very likely that they
do not function as surfactants and consequently not spread the food coloring as
the dish soap did.
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