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?

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?

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?

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?

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?

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?

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?

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

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?

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?

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

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?

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?