Surface Area to Volume ratio

What is the surface area to volume ratio?

It is a measure that compares the surface area of an organism to its volume, influencing heat loss and substance exchange.

How do you calculate the surface area of a cube?

Length x width (area of one side) x 6 (since a cube has 6 sides).

What is the formula for calculating the surface area of a sphere?

4πr², where r is the radius.

How do you calculate the volume of a cube?

Length x width x height.

What is the formula for calculating the volume of a sphere?

4/3πr³, where r is the radius.

What are the ratios always simplified to?

ratios are always simplified to x:1

Always to one so it is easier to compare

What is the relationship between organism size and SA:V?

As organisms get bigger the surface area to volume ratio decreases which means that the surface area is smaller than the volume

Single cell organisms and other small organisms often have a large surface area compared to their volume

What happens to the surface area to volume ratio as organisms get bigger?

The ratio decreases, meaning the surface area becomes smaller than the volume.

Why is diffusion rate quicker in single cell and other small organisms?

exchange substances can diffuse directly in and out of the cell across the cell-surface membrane. The diffusion rate is quick because of the small distances the substances have to travel

Why is diffusion rate slower in multicellular animals and what do they have to combat this?

In multicellular animals, diffusion across the outer membrane is too slow because:

Some cells are deep within the body so there is a bigger distance between them and the outside environment

Larger animals have a low surface area to volume ratio so it's difficult to exchange enough substances to supply a large volume animal through a relatively small outer surface

Therefore they have to develop gas exchange surfaces like gills and lungs and transport systems to reach all the cells like the circulatory system

Relationship between metabolism and SA:V

The rate of heat loss from an organism depends on its surface area.

If an organism has a large volume then its surface area is relatively small which makes it harder for it to lose heat from its body

If an organism is small and has a large surface area heat is lost more easily.

This means that small organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm.

Relationship between heat loss and SA:V

In terms of shape:

Animals with a compact shape have a small surface area relative to their volume

Minimising heat loss

Animals with a less compact shape have a larger surface area relative to their volume

Increases heat loss from their surface

What are the features of an efficient exchange surface?

A large surface area, thin surface for a short diffusion pathway, and a maintained diffusion gradient.

Features of transport system

A suitable medium to carry material

A closed system of vessels that branch to transport and contain the medium

A mechanism to move the medium. Requires pressure differences. Can be achieved by muscular contraction (animals) or use of physical processes like evaporation in water transport plants