AP Biology

Why do we need a respiratory system?

O2

food

ATP

CO2

Need O2 in for aerobic cellular respiration make ATP

Need CO2 out waste product from

Krebs cycle

AP Biology

Optimizing gas exchange High surface area

maximizing rate of gas exchange CO2 & O2 move across cell membrane by

diffusion rate of diffusion proportional to surface area

Moist membranes moisture maintains cell membrane structure gases diffuse only dissolved in water

AP Biology

Gas exchange in many forms…

one-celled amphibians echinoderms

insects fish mammals

endotherm vs. ectothermsize

cilia

water vs. land ••

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Counter current exchange system Water carrying gas flows in one direction,

blood flows in opposite direction

AP Biology

Blood & water flow in opposite directions maintains diffusion gradient over whole length

of gill capillary

maximizing O2 transfer from water to blood

water

blood

How counter current exchange worksfront back

blood

100%15%

5%90%

70% 40%

60% 30%

100%

5%

50%

50%

70%

30%

watercounter-current

concurrent

AP Biology

Gas Exchange on Land Advantages of terrestrial life

air has many advantages over water higher concentration of O2

O2 & CO2 diffuse much faster through air air is much lighter than water & therefore

much easier to pump

Disadvantages keeping large respiratory surface moist

causes high water loss Internal lungs

AP Biology

Terrestrial adaptations

air tubes branching throughout body

gas exchanged by diffusion across moist cells

Tracheae

Lungs Exchange tissue:spongy texture, moist epitheliumAir enters nostrils

Pharynx glottis larynx (vocal cords) trachea (windpipe) bronchi bronchioles air sacs (alveoli)Epithelial lining covered by cilia & thin film of mucus

AP Biology

Alveoli Gas exchange across thin epithelium of

millions of alveoli total surface area in humans ~100 m2

AP Biology

Negative pressure breathing Breathing due to changing pressures in lungs

pulling air instead of pushing it

Autonomic breathing control Medulla sets rhythm & pons moderates it

measures pH of blood & cerebrospinal fluid bathing brain

CO2 + H2O H2CO3 (carbonic acid)

if pH decreases then increase rate of breathing & excess CO2 is eliminated in exhaled air

Nerve sensors in walls of aorta & carotid arteriesin neck detect O2 & CO2 in blood

AP Biology

Diffusion of gases Concentration gradient & pressure

drives movement of gases into & out of blood at both lungs & body tissue

blood lungs

CO2

O2

CO2

O2

blood body

CO2

O2

CO2

O2

capillaries in lungs capillaries in muscle

AP Biology

Hemoglobin Why use a carrier molecule?

O2 not soluble enough in H2O for animal needs hemocyanin in insects = copper (bluish/greenish) hemoglobin in vertebrates = iron (reddish)

Reversibly binds O2

loading O2 at lungs or gills & unloading at cells

cooperativity

heme group

AP Biology

Cooperativity in Hemoglobin Binding O2

binding of O2 to 1st subunit causes shape change to other subunits conformational change

increasing attraction to O2

Releasing O2 when 1st subunit releases O2,

causes shape change to other subunits conformational change

lowers attraction to O2

AP Biology

O2 dissociation curve for hemoglobin

Bohr Shift drop in pH

lowers affinity of Hb for O2

active tissue (producing CO2) lowers blood pH& induces Hb to release more O2 PO2 (mm Hg)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140

More O2 delivered to tissues

pH 7.60

pH 7.20pH 7.40

% o

xyh

emo

glo

bin

sat

ura

tio

n

Effect of pH (CO2 concentration)

AP Biology

O2 dissociation curve for hemoglobin

Bohr Shift increase in

temperature lowers affinity of Hb for O2

active muscle produces heat

PO2 (mm Hg)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140

More O2 delivered to tissues

20°C

43°C37°C

% o

xyh

emo

glo

bin

sat

ura

tio

n

Effect of Temperature

AP Biology

Transporting CO2 in blood

Tissue cells

Plasma

CO2 dissolvesin plasma

CO2 combineswith Hb

CO2 + H2O H2CO3

H+ + HCO3–

HCO3–

H2CO3

CO2

Carbonicanhydrase

Cl–

Dissolved in blood plasma as bicarbonate ion

carbonic acidCO2 + H2O H2CO3

bicarbonateH2CO3 H+

+ HCO3–

carbonic anhydrase

AP Biology

Releasing CO2 from blood at lungsLower CO2

pressure at lungs allows CO2 to diffuse out of blood into lungs

Plasma

Lungs: Alveoli

CO2 dissolvedin plasma

HCO3–Cl–

CO2

H2CO3

H2CO3Hemoglobin + CO2

CO2 + H2O

HCO3 – + H+