B3.1 Gas Exchange

B3.1.1 Gas Exchange

All organisms do it.

Absorb 1 gas → release an other.

Photosynthesis: absorb CO₂ and release O₂.
(aerob)Respiration: absorb O₂ and release CO₂

For small/unicellular organisms; gas exchange can happen at surface and is simple: large SA/V ratio = easy to keep up with needs

For larger organisms: metabol. tissue deep in body → adaptations to exchange gas w atmosphere+water and their own tissue. Also, SA/V ratio is smaller; of full body; not rapid enough gas exchange; specialized gas exchange

B3.1.2 Gas Exchange Surfaces

• Permeable to respiratory gases: CO₂ + O₂

• Thin: to keep diffusion distances short

• Moist: encourage gas diffusion

• Large SA; maximize diffusion

• Concentration gradient: so it actually happens…

Gas exchange surfaces need these in order to exchange rapidly enough

B3.1.3 Concentration gradients

Need to be maintain so O₂ can diffuse into, and CO₂ can diffuse out of the blood.

Gills: water must be continuously passed over gills, continuous blood flow to dense blood vessel network

Lungs: air continuously refreshed (ventilated), continuous blood flow to dense blood vessel network

Maintain conc gradient:

1. New gases on outside

2. New gases on inside

B2.1.4 Mammalian Lungs

Trachea → 2bronchi → bronchioli →alveoli
Alveoli = sacs that allow for gas exchange: one cell thick layer of alveolar cell; blood from pulm art → pulm vein. O₂ into blood, CO₂ out of blood; blue→red.
Layer: type I pneum: normal, 1 cell… type II pneum: secrete surfactant;reduce tension

Adapted for gas exchange:

1. Airways for ventilation

2. Large Surface area:

3. Large capillary beds

4. Short diffusion distances

5. Moist surf area: surfactant

B3.1.5 Lung Structure (bigger)

Thorax/thoracic cavity: closed to outside air, inside = lungs; one opening: mouth.

Diaphragm: large/dome shaped muscle: floor of thorax; contract=flat: increase volume

External intercostal muscles: diagonal from bellybutton to shoulders: contract when inhal

Internal intercostal muscles: contract when exhaling…

Gas free to move always go from high pressure to low pressure: muscles cause pressur

B3.1.5 Inhaling and exhaling

Inhaling/Insparing:taking up O₂:

1. Diaphragm contract: flattens: increase volume of thorax

2. External intercostal muscles contract: raise rib cage up/out: increase V of thorax

3. Pressure is decreased (Boyle P=¹/_V) to below ATM: lung volume increases

4. Partial vacuum: air comes in through mouth/nose: fill lungs w air

Exhaling/Expiring:

1. Diaphragm relax: decrease volume of thorax

2. Internal intercostal muscles contract: move rib cage in/down: decreas V thorax

3. Pressure is increased (Boyle P=¹/_V) to above ATM: lung volume decreases

   1. Air flows/pushed out through mouth/nose

B3.1.6 Lung volume

Spirometer measures it

Tidal volume: typical breathe out
Inspiratory reserve volume: max volume inspired from max of tidal volume
Expiratory reserve volume: max volume expirered from min of tidal volume
Vital Capacity: reserve volumes + tidal volume
Residual volume: whats left in the lungs under exp reserve
Total lung capacity: how much maximum air, from 0…

B3.1.7 Leave structure

Waxy cuticle: oily layer: prevent water loss, but also prevent gas exchange
Upper epidermis: secrete wax
Pelisade Mesophyll: many chloroplasts
Spongy Mesophyll: w. air spaces so O₂/CO₂ can diffuse through; large SA
Lower Epidermis: small cells on lower surf secrete wax. where stomata are.
Phloem/Xylem: supply new water: veins
Stoma/Stomata/Guard cells: pores in epiderm: open&close(night): allow gas exch

Stomatal density: count in right order, and make sure to take absolute measurements

B3.1.8 Leaf tissue photo

B3.1.9 Transpiration

When water evaporates: leaves through stomata:

If air is:
1. Warm: more evap (more energy to break H-bonds)
2. Less humid: more evap (conc. gradient in vs out)
3. Wind: more wind→more trans, however, stomata close when too much wind
4. Light: more light → more photosynthesis → stomata open; more transpiration

B3.1.10 Stomatal density

Measure as number of smatsa per mm/cm/…..

Use nail polish stain to count properly

B3.1.11 Haemoglobin

How erythrocytes: RBC: carry oxygen.

Can carry 4O₂ molecules: saturated. The iron group is what bonds to the O.

Cooperative binding: any O₂ molecule bonding to haemglob increases affinity for more: changes shape of heamoglobin molecule.

Allosteric bind of CO₂: CO₂ can also bind to heamoglob: at polypep part; allosteric site of protein; cause increase in release of O₂ molecules → lower affinity. Bohr shift(b3.1.12)

Foetal haemoglobin: higher affinity to O₂ than mother → conc grad so encourage diffusion of mothers oxygen to foetus, see graph Bohr shift…

B3.1.12 Bohr Shift

Increase in CO₂ conce reduces affinity for O₂ by reducing pH & allosteric binding

Cause lower saturation of heamoglob for same pressure of O₂

See graph.

Happens during excercise etc…; need more oxygen

B3.1.13 Oxygen dissociation curves

At some point all heamoglobin’s full. just know approximately how to differentiate between different graps. When moves right → lower aff. Oxygen