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When an organism is iso-osmotic to its environment, the same number of
ions and water molecules move through the organism's membrane, and there
is an equal concentration of ions and water on both sides of the membrane.
This is illustrated by the left frame.
When the environment has more ions, it is said to be hyper-osmotic to
the organism. The extra ions in the environment pull the water out of
the organism (shown in the center frame). This phenomena is associated
with salt water and explains the ancient mariner's dilemma. It also may
explain why insects have been unable to adapt to the ocean.
When the environment has less ions than the organism living in it, it
is said to be hypo-osmotic. Water tends to flood into the organism whose
ions in turn may move into the environment (shown in the right frame).
This condition is associated with organisms inhabiting freshwater and
does not apply to the ocean environment.
Is the salt of the ocean enough to prevent insects from colonizing
it? Find out
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