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Slide 2

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Most gas exchange surfaces have two common
· They have a large surface area
· They're thin (one cell thick)
- thus a short diffusion pathway
The organism also maintains a steep
concentration gradient of gases across the
exchange surface
These factors.. Increase the rate of diffusion!…read more

Slide 3

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They absorb and release gases by
diffusion through their outer
They have a relatively large
surface area, thin surface and
short diffusion pathway so..
there's no need for a gas
exchange system!…read more

Slide 4

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Due to a lower concentration of oxygen in
water than air, fish needed to adapt;
1) Water enters through the mouth and out
through the gills
2) Each gill's made of numerous thin gill
filaments to give a big surface area for gas
3) The filaments are
covered in tiny
structures called
lamellae that
increase surface area
4) Lamellae have lots of
capillaries and a thin
surface layer of cells…read more

Slide 5

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5) Blood flows through the lamellae in one
direction and water flows over in the other
maintains a large concentration gradient
between water and blood ­ plenty of oxygen
diffuses from the water to the blood.
r…read more

Slide 6

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Have tiny air filled pipes call tracheae to
exchange gas.
Air moves into the tracheae via pores on the
surface called spiracles.
O2 then travels down the concentration
gradient to the cells. CO2 from the cells
moves down its own gradient to the
spiracles to be released into the
The tracheae branch off to smaller tracheoles
with thin, permeable walls that go to
individual cells. So... O2 diffuses straight
into the respiring cells ­ the insects
circulatory system doesn't transport O2 !
They use rhythmic abdominal movements to
move air in and out of the spiracles.…read more

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