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Patterns in Nature
identify and compare the gaseous exchange surfaces in an insect, a fish, a frog and a mammal
Surface in which the diffusion of oxygen and carbon dioxide can occur
External respiratory opening
Large tube strengthened by rings of chitin to allow movement of air to the tissues
Tough, protective substance
Fine respiratory tube branched from tracheae
The diffusion of oxygen into the bloodstream and carbon dioxide out of the bloodstream or body
Lid or covering for an opening
Cavity between jaws and cheeks
Tiny air sacs within the lungs
Branching blood vessel
Respiratory surfaces of animals and humans are determined by individual requirements of oxygen and release of carbon dioxide.
These surfaces are body exteriors which have evolved to become specialised for gaseous exchange with the external environment.
Air is taken in through a row of ‘
on both sides of the abdomen. Spiracles contain valves which allow the regulation of their opening and closing, ensuring prevention of constant exposure to the dry, outer environment.
Air continues into
or ‘tracheal tubes’ which are open by spiral rings of ‘
to prevent collapsing.
Tracheae branch out into smaller tubules known as
. This develops a larger surface area for gaseous exchange.
The ends of tracheoles contain a watery fluid where gases can dissolve. Once oxygen is dissolved in this fluid, it diffuses into the insect’s body cells.
As an insect is more active, more spiracles are open. Therefore, the rate of respiration is controlled by these spiracles.
Unlike other terrestrial vertebrates, insects do not have blood, lungs or capillaries. The intake of air is dependent on a system of inner tubes and valves.
Similar to terrestrial animals, insects possess an internal respiratory surface.
Gas exchange occurs through body pores, not the use of lungs.
Insect respiratory system
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Fish have internal gills which are the respiratory organs.
Water moves in one direction throughout the fish. It begins as it enters the mouth, flows over the gills and lifts its gill coverings known as
in order to let the water out.
The floor of the mouth called the ‘
assists with the movement of water.
Gaseous exchange occurs when water flows over the gills.
Water movement reduces because of the gill filaments which are of a highly branched nature, and also because of the closely stacked gills which rely on the flow of water to be kept apart.
There are four curved gill arches which are stacked together on both sides of the pharynx (through), which are covered by an ‘
Both gills have two rows of delicate gill filaments, divided to increase surface area.
Gases can enter and leave easily due to the thin layer of cells on each filament. Oxygen diffuses into the blood capillaries within the gill filaments whilst carbon dioxide is diffused out.
Gas exchange occurs using the gills, which increases surface area.
This high surface area is required as there is much less oxygen within water than there is in air.
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Adult frogs use three surfaces for gaseous exchange:
Main site for respiration once in water or once inactive on land
Supplied with blood vessel
2. Floor of the mouth
Supplies with blood capillaries
Ventilates lungs as a buccal pump
3. Two sac-like lungs
Lungs are in use for gaseous exchange when physically active.
Nostrils contain valves which prevent movement of water into lungs whilst swimming
All surfaces are thin, moist and supplied with blood vessels.
The lungs are not in use all the time.
Other surfaces are utilised when the frog is inactive compared to other organisms where lungs are in constant function.
When active, lungs are in use similar to humans.
Gas exchange occurs in
or air sacs within the lungs. They provide a boundary between the external environment and the capillaries.
The lungs contain features for an efficient gas exchange surface:
- Increased surface area
- Well supplied with blood
As gases move between the air within the alveoli(external environment) and the bloodstream(internal environment) within the capillaries, they must cross a thin barrier of alveolar cells and one layer of capillary cells.
As oxygen within the incoming alveolar air is of higher concentration that that within the bloodstream, oxygen diffuses from the alveoli to the body.
Carbon dioxide is of higher concentration within the bloodstream, so it must diffuse from the capillaries, through the alveolar lining and then to the alveolar air where it will eventually be breathed out.
Gas exchange occurs with complete use of the lungs, like the frog.
Use of blood, capillaries and lungs, similar to the fish and frog.
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161 to 168 for more information
Describe one feature of the respiratory surface for each organism.
How does the insect differ from the other organisms in terms of gaseous exchange?
How does the fish differ from the other organisms in terms of gaseous exchange?
How does the frog differ from the other organisms in terms of gaseous exchange?
How does the mammal (human) differ from the other organisms in terms of gaseous exchange?
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