1. Respiratory Systems Why the need for gas exchange (respiration)?
Gas exchange involves uptake of O2 and release of CO2
What is oxygen used for?
Aerobic respiration uses energy of electrons to produce ATP
Energy-depleted electrons (and associated proton in H) accepted by O2 to form H2O
Where does CO2 come from?
CO2 released when glucose broken down to release electrons in the Kreb’s Cycle
How do organisms ‘solve’ common problems?

2. Respiratory Systems Respiration involves diffusion
Respiration requires diffusion of O2 and CO2 across cell membranes
Diffusion of O2 and CO2 is passive
Occurs if different concentrations of O2 or CO2 on either side of membrane
How do organisms ‘solve’ common problems?

3. Respiratory Systems What determines rate of diffusion?
Rate of diffusion described by Fick’s Law of Diffusion:
Difference in concentration on either side of membrane
Rate of diffusion (amount of gas per unit time)
Diffusion constant
Area over which diffusion takes place
Distance across which diffusion takes place
How do organisms ‘solve’ common problems?

4. Respiratory Systems
How can rate of diffusion be maximized by natural selection?
R increased if:
Increase area (A) of respiratory surface
Increase difference in concentration (DP) on either side of respiratory surface
Decrease distance (d) over which gases must travel
How do organisms ‘solve’ common problems?

5. Respiratory Systems Basic types of respiratory systems in animals
Direct diffusion through cells
Phyla Cnidaria
How to maximize rate of diffusion?
thin cell or tissue layers
circulate water across outer surface (maintain DP)
What constraints are associated with this system?
cannot be large in size
Cannot be involved in energy-consuming activities
How do organisms ‘solve’ common problems?

6. Respiratory Systems Basic types of respiratory systems in animals
Cutaneous (skin) respiration
Phyla Annelida
How to maximize rate of diffusion?
thin skin
Increase surface area with parapodia
Use cilia on skin to move water (maintain DP)
What constraints are associated with this system?
cannot get too large
No energetically expensive activities
How do organisms ‘solve’ common problems?

7. Respiratory Systems Basic types of respiratory systems in animals
External Gills
Phylum Chordata
larval fish and amphibians (also in some adult salamanders)
How to maximize rate of diffusion?
thin gills
Increase surface area with feather-like arrangement of gills and by using skin as additional respiratory surface
What constraints are associated with this system?
Must be in constant motion or in water current
Tissue delicate and cannot be protected
Relatively small body size
How do organisms ‘solve’ common problems?

8. Respiratory Systems
Neotenic salamander (development arrested in juvenile stage; adults have external gills)
How do organisms ‘solve’ common problems?

9. Respiratory Systems Basic types of respiratory systems in animals
Internal (covered) Gills
Phylum Chordata
Bony fish (Class Osteichthyes)
Internal gills enclosed within body chambers that move water over gills
Buccal cavity (mouth)
Opercular cavity (gill chamber below gill cover or operculum)
Two cavities act together to draw water across surface of gills
How do organisms ‘solve’ common problems?

10. Respiratory Systems Basic types of respiratory systems in animals
Internal (covered) Gills
How to maximize rate of diffusion?
thin gills (blood vessels close to surface of gill)
Increase surface area of gill with feather-like arrangement
Constantly ‘pump’ water across gills with buccal and opercular cavities
Uses counter-current system in gills to increase DP
How do organisms ‘solve’ common problems?

11. Respiratory Systems Basic types of respiratory systems in animals
Structure of Internal Gills
How do organisms ‘solve’ common problems?

12. Respiratory Systems Basic types of respiratory systems in animals
Water flows over surface of lamellae of gills within which are capillaries
flow of blood in capillaries is opposite flow of water = counter-current system of gas exchange
How do organisms ‘solve’ common problems?

13. Respiratory Systems Basic types of respiratory systems in animals
Internal Gills
What constraints are associated with this system?
Gills very efficient in water but do not work on land
Gills lack support needed in less-buoyant air
Air is relatively dry and all respiratory surfaces must be moist (gas exchange must occur in water); gills have large surface area exposed to dry air
How do organisms ‘solve’ common problems?