When an insect is changing inside its cocoon, and has turned to slush, is it alive? And if so, in what way is it alive?
In many metamorphosing insects, the majority of the cells in the body of the pupa do break down and turn to mush, but there are clusters of cells that remain intact. These cells feed on the mush, divide, and go on to develop the legs, eyes, wings, antennae and so on that we see in adult insects.
鈥淐lusters of cells in a cocoon feed on the mush and go on to develop the legs, eyes, wings and antennae of adult insects鈥�
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It is almost as though the mush is the yolk and the cluster of cells is the embryo of a new egg. In some rare cases, such as fungus gnats, this new embryo can split to form multiple 鈥渢win鈥� adults from a single larva. This is called polyembryony.
Martin Harris, Australia
An insect undergoing metamorphosis is alive regardless of what state its body may be in. For one thing, the individual cells are alive and are growing and dividing in a coordinated manner to form the organs of the new adult insect. An insect, or any other organism, could not be dead at one stage of its development and alive at a following stage, because the death of an organism is always irreversible.
However, the death of a multicellular organism such as an insect must be defined separately at different levels of organisation: the intact body; the organs and tissues; and finally, the individual cells. The body cannot survive without organs and cells, but the latter two groups can survive without a body. If you squash a cocoon the larva inside will be killed, but many of its cells will remain alive, at least for a while. Therefore, a multicellular organism can be killed by destroying its highest level of organisation, while leaving most of its organs and cells alive. If that were not the case, there would not be such possibilities as human organ transplantations or cell cultures.
Aydin Orstan, Germantown, Maryland, US
What is meant by alive? Is the ball of cells that make up the human blastocyst alive? It cannot breathe, think or feel pain. But it is alive, like the mush of insect cells in a cocoon. The cells that make up both structures are metabolising, dividing and responding to their environment 鈥� all hallmarks of life.
Roger Morton, Dunlop, Australian Capital Territory