Gas Exchange Surfaces And Cell Membranes

Large surface area to volume ratio; thin exchange surface / short diffusion distance; steep concentration gradient between the two sides

Has a high surface area to volume ratio; gases can diffuse directly across the cell membrane; diffusion distance to all parts of the cell is short

Large body size means low surface area to volume ratio; diffusion across body surface alone cannot meet metabolic demand for oxygen

Rate of diffusion is proportional to surface area × concentration difference; divided by membrane thickness

Rate of diffusion decreases by 50% / falls to 50% of normal; because surface area is directly proportional to rate of diffusion

Increases diffusion distance; rate of diffusion is inversely proportional to thickness; less oxygen enters the blood / less CO₂ leaves the blood per unit time

Alveolar wall one cell thick / made of squamous epithelium; capillary wall one cell thick / made of endothelium

Brings in fresh air with high oxygen concentration; removes air with high carbon dioxide concentration; maintains steep concentration difference between alveolar air and blood

Many alveoli provide a large total surface area of around 70 m² / increases SA term in Fick’s Law; alveolar wall is one cell thick (squamous epithelium) / reduces diffusion distance / reduces thickness term; capillary wall is also one cell thick (endothelium) / further reduces diffusion distance; ventilation continuously replaces alveolar air / brings in O₂ and removes CO₂ / maintains steep concentration gradient; continuous blood flow / removes oxygenated blood and delivers deoxygenated blood / maintains concentration difference; dense capillary network / brings blood in close contact with alveolar surface / maximises area of contact

Form a bilayer; hydrophilic phosphate heads face outward toward water / aqueous environment; hydrophobic fatty acid tails face inward / away from water

Regulates membrane fluidity; keeps membrane stable across a range of temperatures / prevents membrane becoming too fluid at high temperatures or too rigid at low temperatures

Intrinsic proteins span the entire phospholipid bilayer / extrinsic proteins are attached to only one surface; intrinsic often act as channels or carriers / extrinsic often act as receptors or structural support

Fluid because phospholipids can move laterally within the bilayer; mosaic because proteins are scattered throughout the membrane in an irregular pattern

Fluorescent labelling experiments showed proteins from fused mouse and human cells mixed within minutes; demonstrating membrane proteins move laterally / OR Freeze-fracture electron microscopy revealed proteins embedded throughout the bilayer; rather than as continuous layers on each side

New evidence such as freeze-fracture electron microscopy showed proteins were embedded within the bilayer; not arranged as continuous outer layers; models in science are revised when they fail to explain new data

Independent variable: temperature in °C / alcohol concentration in % (or both); dependent variable: absorbance of solution at 530 nm / amount of pigment leaked

Heat increases kinetic energy of phospholipids; phospholipid bilayer becomes more fluid / gaps appear; membrane proteins begin to denature / lose tertiary structure / channel proteins damaged; betalain pigment leaks out more rapidly

To control surface area; different surface areas would result in different rates of pigment leakage / would confound the independent variable

At very low temperatures, phospholipids become less fluid / membrane becomes more rigid; cholesterol and phospholipid arrangement disrupted / membrane proteins may be damaged by cold; allowing more pigment leakage