3.3.1. - Surface area to volume ratio

What happens to surface area : volume ratio as an organism gets larger?

The larger an organism is, the smaller it’s surface area is relative to its volume - sa : v ratio gets smaller

Do small organisms have a high or low surface area : volume ratio?

They have a very large surface area relative to their volume - high sa : v ratio

Small organisms have a large surface : volume ratio, what does this mean for the exchange of substances?

This means there is a big surface for exchange of substances and also a smaller diffusion distance. Therefore they can simply exchange substances across their surface - unlike large organisms.

Why do large organisms require specialised exchange systems?

They have less surface area relative to their volume for the exchange of substances like oxygen and heat therefore need a way of transporting them efficiently

Why do small mammals lose heat quickly?

Because they have a high surface area : volume ratio so have a higher amount of heat loss

What is metabolic rate?

The total energy used by an organism per unit time

How is metabolic rate measured? (2 ways)

• Oxygen consumption

• Carbon dioxide production

Why is a high metabolic rate useful for small mammals - especially in cold environments?

It supplies the energy needed to provide more heat and maintain a stable body temperature

Why do larger organisms have a lower metabolic rate?

Because they lose heat more slowly due to their high surface area : volume ratio