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Terrestrial organisms
Water easily evaporates off terrestrial
organisms' bodies and they can become
dehydrated.
However, efficient gas exchange requires thin,
permeable surfaces with a large area; this
conflicts with the need to conserve water.
But these organisms need to balance these
opposing needs.…read more

Slide 3

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Conserving water
To conserve water insects have a rigid outer skeleton
covering their bodies which has a waterproof cuticle.
They also have a small surface area : volume ratio.
Gas exchange
Insects can't use their body surface to diffuse respiratory
gases instead they have a network of tubes called
tracheae.…read more

Slide 4

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Gas exchange system of an insect
Tracheae are supported by strengthened rings to
prevent them from collapsing.
Tracheae divide into smaller tubes called tracheoles.
These extend throughout all the body tissues.
This way, atmospheric air is brought directly to respiring
tissues.
Gases enter and leave through the spiracle, which is
opened by a valve; when open H20 can evaporate.…read more

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Tracheal system
This system provides enough oxygen for small
insects by diffusion. But larger insects need
oxygen more rapidly.
To achieve this the spiracle closes and
muscles pull the skeletal pates of the
abdominal segments together. This squeezes
the tracheal system and pumps the air in the
air sacs deeper into the tracheoles.…read more

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Tracheoles supplying tissue cells
Additional oxygen reaches deep into the muscles
during flight because:
When an insect is resting, some water leaks across the cell
membranes of muscle cells, as a result very narrow ends of
the tracheoles fill with water.
When the wing muscles are working hard they respire
partly anaerobically and produce lactate.
Water potential of muscle cells is lowered as this lactate
builds up in the muscle cells, so water passes from the
tracheoles into the muscle cells.
This draws air in the tracheoles closer to
the muscle cells and therefore reduces
diffusion distance for O2 when it's most
needed.…read more

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