A-Level Biology - 3.3.1 Surface area to volume ratio

What is the equation to calculate surface area to volume ratio?

organism or structure's surface area/its volume

Describe the relationship between the size of an organism or structure and its surface area to volume ratio

as the size of an organism increases, its surface area to volume ratio decreases

Is diffusion across its surface a viable transport mechanism in large organisms? Why?

No, because there is a small surface area to volume ratio and a large diffusion distance

so the time taken for substances to diffuse from the cell surface membrane to the tissues would be too long

large organisms also have a higher metabolic rate, so their metabolic demands could not be met by diffusion across its surface

Is diffusion across its surface a viable transport mechanism in small organisms? Why?

Yes, because they have a large surface area to volume ratio and there is a short diffusion distance between the surface and the centre of the organism

so the time taken for substances to diffuse from the cell surface membrane to the tissues is quick

also they have a relatively low metabolic rate

Why do larger organisms need a specialised exchange surface for oxygen?

They have a smaller SA:V

It overcomes long diffusion pathway, leading to quicker diffusion

What is metabolic rate?

the amount of energy an organism uses in a unit of time

Describe the relationship between the mass of an organism and metabolic rate

the greater the mass of the organism, the higher its metabolic rate