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 What’s Inside A Caterpillar 'Cocoon?'
작성자
 이** (jean)
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Description: 

Contrary to popular belief, a chrysalis is not a pouch or a sac —It’s actually 

the caterpillar’s own body! During metamorphosis, the former caterpillar 

releases digestive juices that dissolve cells in its muscles, gut, and other

organs. Then, special groups of cells called imaginal discs divide over and 

over again, forming wings and other adult structures. 

 

Transcription: 

What would you do for the power to fly? How about shedding your skin and 

dissolving your own muscles? Now, believe it or not, that gruesome process 

is how caterpillars earn their wings. Here's what you might not know about 

what's inside a caterpillar's "cocoon." Contrary to popular belief, this is not

a cocoon. Only certain moths build cocoons, which are like a silky sleeping

bag that covers the insect. This, on the other hand, is what's called a chrysalis.

It's not a sack or a pouch; it's actually the caterpillar's own body. 

When it's time for the transformation to begin, the caterpillar's body ramps 

up production of a hormone called ecdysone, and that causes it to cast off

its outer coating, sort of like how a snake sheds its skin. And underneath

is a hard shell similar to the exoskeleton of a beetle. After that, life for the

little caterpillar gets oozy. First, it releases enzymes called caspases. 

These rip apart and dissolve cells in its muscles, digestive system,

and other organs. But the enzymes don't quite liquefy all of the caterpillar.

They leave key structures intact, like breathing tubes. At the same time, 

specialized cells called imaginal discs start waking up. Before the chrysalis 

stage, these discs were kept dormant by a series of hormones in the 

caterpillar's body. But once the transformation begins, those hormone 

levels take a nosedive, giving these discs the opportunity to do what they 

do best: build a butterfly. You see, each disc contains the genetic recipe

to form a different adult body part, starting from the inside out. After one 

week, the digestive system of the butterfly is well on its way. 

And by day 16, the adult's legs, wings, eyes, and mouth are all present 

and in working order. Now, two weeks is a remarkably short time for all of 

this to happen, since each imaginal disc starts out with only about 50 cells

and must multiply those into thousands just to form a single wing. And if 

you checked out the chrysalis around day 16, you might even be able to

see those brilliantly colored wings. Because for some species, their chrysalis

turns transparent in their final days of metamorphosis. Now, fully formed, 

it's time to hit the road. The chrysalis splits open down the center, and the

butterfly escapes. Meanwhile, a reddish liquid spills out. That's all the waste

the butterfly, née caterpillar, produced during its stay. Once its wings expand

and harden, it's ready to mate, pollinate, and slurp nectar to its heart's desire.

But one of the most interesting parts of all? Research suggests that butterflies

and moths can remember their caterpillar days. In one study, researchers trained

moth caterpillars to associate an odor with an electric shock, so whenever the

larvae smelled it, they'd move away. But even after they transformed into adult 

moths, they still avoided the scary smell. It makes you wonder what else they

could recall from their younger days. 

 

Questions: 

1. What is the difference of a cocoon and a chrysalis?

2. Explain how a catterpilar transform into a butterfly? 

3. Talk about the study done by the scientists.

작성일자
2021-02-02 오후 2:13:14
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