戴爾美語托福TOP解析 - 英檢

Professor:
Ok, now I want to talk about an animal that has a fascinating set of
defense mechanisms. And that's the octopus, one of the unusual creatures
that live in the sea. The octopus is prey to many species, including
humans, so how does it escape its predators?
(1) Well, let me back up here a second. Anyone ever heard of Proteus?
Proteus was a God in Greek mythology who could change form.
He could make himself look like a lion or a stone or a tree,
anything you wanted, and he could go through a whole series of changes
very quickly.
Well, the octopus is the real world version of Proteus.
Just like Proteus, the octopus can go through all kinds of incredible
transformations. And it does this in three ways: by changing color,
by changing its texture, and by changing its size and shape.
For me, the most fascinating transformation is when it changes its
color. It's a normal skin color, the one it generally presents,
is either red or brown or even grey, and it 's speckled with dark
spots. (2) But when it wants to blend in with its environment to hide
from its enemies, it can take on the color of its immediate
surroundings: the ocean floor, a rock, a piece of coral, whatever.
Charles?

Student:
Do we know how that works, I mean, how they change colors?

Professor:
Well, we know that the reaction that takes place is not chemical
in nature. The color changes are executed by two different kinds of
cells in the octopus ' skin, mainly by color cells on the skin's
surface call chromatophores.
Chromatophores consist of tiny sacks filled with color dye.
There might be a couple hundred of these color sacks per square
millimeter of the octopus ' skin, and depending on the species,
they can come in as many as five different colors.
Each one of these sacks is controlled by muscles.
If the muscles are relaxed, the sack shrinks,
and all you see is a little white point. But if the muscle's contract,
then the sack expands, and you can see the colors.
And by expanding different combinations of these color sacks to
different degrees, the octopus can create all sorts of colors.
Yes, Elizabeth?
Student:
And just with various combinations of those five colors,
they can recreate any color in their environment?

Professor:
Well, they can no doubt create a lot with just those five colors,
but you are right, maybe they can't mimic every color around them,
so that's where the second kind of cell comes in.
Just below the chromatophores is a layer of cells that reflect light
from the environment, and these cells help the octopus create a
precise match with the colors that surround them.
The colors from the color sacks are supplemented with colors that are
reflected from the environment, and that 's how they are able to
mimic colors with such precision. So, that's how octopus mimic colors.
But they don't just mimic the colors in their environment;
they can also mimic the texture of objects in their environment.
They have these little projections on their skin that allow them to
resemble various textures. The projections are called papillae.
(3) If the octopus wants to have a rough texture, it raises the
papillae. If it wants to have a smooth texture, it flattens out the
papillae, so it can acquire a smooth texture to blend in with the
sandy bottom of the sea. So the octopus has the ability to mimic both
the color and the texture of its environment.
And it's truly amazing how well it can blend in with its surroundings.
You can easily swim within a few feet of an octopus and never see it.

Student:
I read that they often hide from predators by squirting out a cloud of
ink, or something like that.

Professor:
Yes. The octopus can release a cloud of ink if it feels threatened.
But it doesn't hide behind it, as is generally believed. Um, the ink
cloud is ... it serves to distract a predator while the octopus makes
its escape.
(4) Um, now there's a third way that octopus can transform themselves
to blend in with or mimic their environment, and that's by changing
their shape and size, well, at least their apparent size.
The muscular system of the octopus enables it to be very flexible to
assume all sorts of shapes and postures. So it can contract into the
shape of a little round stone, and sit perfectly still on the seafloor.
Or it can nestle up in the middle of a plant and take the shape of
one of the leaves. Even Proteus would be impressed, I think.

Question 1：
Why does the professor first mention Proteus?
A. To explain how the octopus got its scientific name.
B. To introduce the octopus' exceptional abilities.
C. To point out that the octopus played an important role in Greek mythology.
D. To provide an example of a mythological character that was part animal
and part human.

Question 2：
How does an octopus change color to match the colors in its environment?
Click on 2 answers
A. By raising its papillae.
B. By releasing colored ink.
C. By reflecting light from its environment.
D. By contracting the muscles around its chromatophores.

Question 3：
What does the professor say about the function of the papillae?
A. They produce dye in different colors.
B. They propel the octopus through the water.
C. They change the texture of the octopus' skin.
D. They help the octopus contract into a smaller shape.

Question 4：
What two examples does the professor mention to describe the octopus' ability
to change its shape? Click on 2 answers
A. A small round stone
B. The leaves of a plant
C. A cloud of ink.
D. A piece of coral.

詳細解答請參考: http://allenglishtoefljj.blogspot.tw/2015/07/biology-octopus-tpo-17.html
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