Surface area to volume ratio

What is the surface area to volume ratio?

The surface area relative to the volume of an organism or structure.

What happens to SA:V ratio as an organism increases in size?

SA:V ratio decreases because volume increases proportionally more than surface area.

Why can small organisms rely on diffusion?

They have a large SA:V ratio, allowing a faster rate of exchange and a shorter diffusion pathway.

Why can't large organisms rely on diffusion alone?

They have a smaller SA:V ratio, so there is less surface area available for exchange relative to their volume and diffusion is too slow to meet the requirements of cells.

How do larger organisms overcome their smaller SA:V ratio?

They develop specialised exchange surfaces and mass transport systems to facilitate exchange.

How does a large surface area increase the rate of diffusion?

A larger surface area provides more area across which diffusion can occur, increasing the rate of exchange.

How does a short diffusion pathway increase diffusion rate?

A shorter diffusion pathway increases the rate of diffusion.

What is the relationship between SA:V ratio and metabolic rate?

As SA:V ratio increases, metabolic rate increases. A larger SA:V ratio results in more heat loss, so a higher metabolic rate is required to release/provide heat and maintain body temperature.