Gas Exchange

Gas Exchange: physical process by which gases move passively by diffusion across a membrane

Gases either enter or leave the body of an organism

Gas exchange is a vital process in all organisms as it is necessary to capture and use energy

• Respiration and photosynthesis

• Metabolism

• Waste removal

• Homeostasis

• Survival in various environments

• Nutrient transport

• Ecosystem balance

Surface area to volume ratio is inversely proportional to size

As a species increases in size, the distance from the centre of the organisms to its exterior increases

As an organism increases in relative size, the metabolic rate decreases

Eventually reach a lower limit of metabolism needed for the organism to survive

Bacteria and protozoa (small unicellular organisms)

High SA:V

Gas exchange is typically the cell membrane itself

Insects

Evolved a respiratory system (tracheal system)

Consists of a network of tiny tubes (trachea) that branch throughout the insects body, delivering oxygen to cells and tissues

Larger Organisms

Smaller SA:V

Specialised structures with convoluted surfaces (gills, lungs and spongy mesophylls) provide the large surface area needed for gas exchange

Gas exchange surface: simply refers to the surface tissue or membrane at the site of gas exchange in an organism

Gas exchange surfaces have unique features that enable gases to move efficiently:

• Permeability - cell membranes or specialised tissues on the GES must be selectively permeable to allow gases to pass through while preventing the loss of essential fluids

• Thickness - thin tissues minimise the barrier that gases must cross, ensuring that diffusion occurs quickly and efficiently

• Moisture - gases like oxygen and carbon dioxide are more soluble in moist substances than in dry ones (reduces surface tension allowing gasses to move at a higher rate)

• Surface area - structures that increase surface area (in cells = folds, projections) (in organs = specialised structures like alveoli or gill filaments) allowing for more gas molecules to be exchanged simultaneously, increasing overall efficiency

Average adult human lung contains between 300-500 million alveoli