Describe the structures involved in gas exchange in the human respiratory system and compare it to other organisms.

a)
P: Trachea
Q: Ribs

b) The function of part R (intercostal muscles) is to contract and relax to move the rib cage during breathing, facilitating inhalation and exhalation.

c) Part S (alveoli) is adapted to its function of gas exchange by having:

• A large total surface area for efficient diffusion of gases.
• Thin walls (one cell thick) to reduce the diffusion distance.
• A rich blood supply (capillary network) to maintain a steep concentration gradient for gases.
• A moist surface to dissolve gases, allowing for easier diffusion.

d) The structure that performs the same function (gas exchange) as the illustrated system in:

i) Amoeba: Cell membrane

ii) Fish: Gills