The secret of metamorphosis
The caterpillar is actually only oneof two possible forms of the same creature. Although all the cells of the caterpillar and butterfly are identical they differ in that some cells have the caterpillar genes switched off and the butterfly genes switched on and the rest have the caterpillar genes turned off and the buttefly genes switched on. Initially, it is the cells that have the caterpillar genes switched on that are encouraged to grow under the chemical influence of hormones. When the caterpillar matures the cells with the butterfly genes turned on are stimulated into action at the expense of the caterpillar cells.
A chemical, hormone, sweeps across the cells and tags some of them to become caterpillar cells. A while later a second chemical sweeps across and assigns the rest of
the cells to the development of the butterfly body parts. Now the egg
consists of identical cells with specialised functions. The cells committed
to the formation of the caterpillar are now encouraged to grow in size
while those cells responsible for the butterfly body parts lie dormant
amongst the caterpillar cells. The butterfly cells lie in the body of
the caterpillar in small groups called imaginal disks and are prevented
from developing by a chemical called juvenile hormone that circulates
in the caterpillar's blood. The imaginal disks grow as the caterpillar
grows, taking food from the caterpillar in a kind of parasitic existence.
When the caterpillar has fully matured, the secretion of juvenile hormone ceases and the butterfly cells start to develop. The absence of juvenile hormone also triggers the death of the caterpillar cells, their death and eventual breakdown will provide the nourishment to feed the butterfly cells.
Explain what is happening inside the pupa as it rests?
Answer true or false
The caterpillar is a different organism to the butterfly
Caterpillar cells turn into butterfly cells while in the pupa.
The egg contains only caterpillar cells
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