• Why the need for gas exchange (respiration)?

Respiratory Systems

How do organisms ‘solve’ common problems?

– 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

• Respiration involves diffusion

Respiratory Systems

How do organisms ‘solve’ common problems?

– 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

• What determines rate of diffusion?

Respiratory Systems

How do organisms ‘solve’ common problems?

– Rate of diffusion described by Fick’s Law of Diffusion:

RDAPd

Rate of diffusion (amount of gas per unit time)

Diffusion constant

Area over which diffusion takes place

Difference in concentration on either side of membrane

Distance across which diffusion takes place

• How can rate of diffusion be maximized by natural selection?

Respiratory Systems

How do organisms ‘solve’ common problems?

– R increased if: • Increase area (A) of respiratory surface

RDAPd

• Increase difference in concentration (P) on either side of respiratory surface

• Decrease distance (d) over which gases must travel

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– Direct diffusion through cells

• How to maximize rate of diffusion? – thin cell or tissue layers

• What constraints are associated with this system?

– circulate water across outer surface (maintain P)

– cannot be large in size

• Phyla Cnidaria

– Cannot be involved in energy-consuming activities

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– Cutaneous (skin) respiration

• How to maximize rate of diffusion? – thin skin

• What constraints are associated with this system?

– Increase surface area with parapodia

– cannot get too large

– No energetically expensive activities

– Use cilia on skin to move water (maintain P)

• Phyla Annelida

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– External Gills • Phylum Chordata

– thin gills

• What constraints are associated with this system?

– Increase surface area with feather-like arrangement of gills and by using skin as additional respiratory surface

– Must be in constant motion or in water current

– Tissue delicate and cannot be protected

• larval fish and amphibians (also in some adult salamanders) • How to maximize rate of diffusion?

– Relatively small body size

• Neotenic salamander (development arrested in juvenile stage; adults have external gills)

Respiratory Systems

How do organisms ‘solve’ common problems?

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– Internal (covered) Gills • Phylum Chordata

– Buccal cavity (mouth)

• Two cavities act together to draw water across surface of gills

– Opercular cavity (gill chamber below gill cover or operculum)

• Bony fish (Class Osteichthyes)• Internal gills enclosed within body chambers that move water over gills

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– Internal (covered) Gills

– thin gills (blood vessels close to surface of gill)

– Increase surface area of gill with feather-like arrangement

– Uses counter-current system in gills to increase P

• How to maximize rate of diffusion?

– Constantly ‘pump’ water across gills with buccal and opercular cavities

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– Structure of Internal Gills

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– 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

• Basic types of respiratory systems in animals

Respiratory Systems

How do organisms ‘solve’ common problems?

– 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