1. Gas Exchange in Animals
All living things respire – release energy from food.

2. To respire oxygen has to come in across a membrane, be carried to the cells and carbon dioxide released.
Gas exchange is movement of gases across a membrane.
Breathing is the physical movements that help GE.

3. Animals need a respiratory surface. All have 3 main requirements:
Must be moist, gas has to be dissolved in water to pass over membrane
Large to maximise gas exchange
Thin to allow gas to diffuse across

4. Different Gas Exchange Surfaces

5. Diffusion across a membrane
Protozoa, hydra and jellyfish
It’s cells are bathed in water and as it is only 1 or 2 cells thick the diffusion is efficient and requires no energy.
Oxygen passes straight into cells where concentration is lower.

6. Diffusion is an effective means of
transporting gases only when the distance is
< 1 mm

7. Open circulatory systems greatly increase the efficiency of transport of substances within a body compared to diffusion

8. Insects – trachea systems
Throughout the insect is a system of hollow tubes (trachea) that reach every cell. They open to the outside through spiracles (small holes) in the exoskeleton along the side of the body. Oxygen diffuses in through the trachea. They are held open by chiton bands.
Some insects also use air sacs, some pump bodies.

10. Closed circulatory systems are even more efficient than open circulatory systems
Fig. 42.3

11. Fish - gills The respiratory system is external to body.
It is made of thin filaments supported by bony structures. Each filament is a delicate plate of capillaries.
Fish continuously pump water through respiratory surface.
They use the counter current
exchange system.

12. Fish gills Gill capillaries are the sites of gas exchange
with the environment

13. Counter-current exchange helps maximize the efficiency of gas exchange

14. Terrestrial vertebrates - lungs
Inside the body cavity so needs an efficient transport system to connect to gas outside body.

15. Human Gas Exchange
Air enters through nose passes to pharynx, then larynx to trachea. Branches down the two bronchi then to bronchioles and finally alveoli. These are covered by capillaries and O2 diffuse in and CO2 out over the thin surface.

16. Ventilation of lungs
Inhalation: breathing in, diaphragm lowered, rib muscles contract, making partial vacuum which pulls air in.
Exhalation: breathing out. Everything relaxes and forces air out.