Tulisan 7 B.Inggris Bisnis 2
As children,
many of us learn about the wondrous process by which a caterpillar morphs into
a butterfly. The story usually begins with a very hungry caterpillar hatching
from an egg. The caterpillar, or what is more scientifically termed a larva,
stuffs itself with leaves, growing plumper and longer through a series of molts
in which it sheds its skin. One day, the caterpillar stops eating, hangs upside
down from a twig or leaf and spins itself a silky cocoon or molts into a shiny
chrysalis. Within its protective casing, the caterpillar radically transforms
its body, eventually emerging as a butterfly or moth.
But what does that radical transformation entail? How does a caterpillar
rearrange itself into a butterfly? What happens inside a chrysalis or cocoon?
First, the caterpillar digests itself, releasing enzymes to dissolve all of its
tissues. If you were to cut open a cocoon or chrysalis at just the right time,
caterpillar soup would ooze out. But the contents of the pupa are not entirely
an amorphous mess. Certain highly organized groups of cells known as imaginal discs survive the digestive process. Before
hatching, when a caterpillar is still developing inside its egg, it grows an imaginal disc for each of the adult body parts it
will need as a mature butterfly or moth—discs for its eyes, for its wings, its
legs and so on. In some species, these imaginal discs remain dormant throughout
the caterpillar's life; in other species, the discs begin to take the shape of
adult body parts even before the caterpillar forms a chrysalis or cocoon. Some
caterpillars walk around with tiny rudimentary wings tucked inside their
bodies, though you would never know it by looking at them.
Once a caterpillar has disintegrated all of its tissues except for the imaginal
discs, those discs use the protein-rich soup all around them to fuel the rapid
cell division required to form the wings, antennae, legs, eyes, genitals and
all the other features of an adult butterfly or moth. The imaginal disc for a
fruit fly's wing, for example, might begin with only 50 cells and increase to more than 50,000 cells by
the end of metamorphosis. Depending on the species, certain caterpillar muscles
and sections of the nervous system are largely preserved in the adult
butterfly. One study even suggests that moths remember what they
learned in later stages of their lives as caterpillars.
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