5 gas exchange in animals (fish and insects)

how does an amoeba exchange gases?

unicellular organism → gases diffuse directly across its thin cell membrane. it has a large surface area to volume ratio, so diffusion is quick and efficient. it lives in moist conditions, allowing gases to dissolve easily.

how does a flatworm exchange gases?

flat body increases surface area and reduces diffusion distance. gases diffuse directly across the surface. it must live in moist environments to keep the surface suitable for gas exchange.

how does an earthworm exchange gases?

gases diffuse through its moist skin, which is covered in mucus. capillaries beneath the skin carry gases to and from cells, and haemoglobin transports oxygen. it must stay moist.

how do insects exchange gases?

through a tracheal system: air enters spiracles, travels through tracheae and tracheoles, and diffuses directly to cells. ventilation movements help airflow, and spiracles close to reduce water loss.

how do fish exchange gases?

using gills made of filaments and lamellae, giving a large surface area and short diffusion distance. countercurrent flow between water and blood maintains a steep oxygen gradient. water flow is kept constant by mouth and operculum movement.

how do amphibians exchange gases?

through moist skin when in water and using lungs on land. buccal pumping helps ventilation, and both skin and lungs have a rich capillary network.

how do mammals (humans) exchange gases?

in the alveoli of the lungs, which have a large surface area, thin moist walls, and a dense capillary network. ventilation keeps concentration gradients steep for o₂ and co₂.

why do multicellular animals need specialised gas exchange systems?

they have a low surface area to volume ratio, so diffusion alone is too slow. they need specialised surfaces (lungs, gills, tracheae) and transport systems (blood) for efficient gas exchange.