Surface area to volume ratio

Explain how the size of an organism affects its surface area to volume ratio, and why this is important.

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

Changes to body shape and the development of systems as adaptations that facilitate exchange as this ratio reduces.

Explain how the body shape of a Weddell seal is an adaptation to living in a cold environment.

Small SA:VOL so reduces heat loss

Use your knowledge of surface area to volume ratio, to explain adaptations to body shape or the development of echange systems

Calculate surface area to volume ratios when supplied with cell/organism dimensions

Describe and explain the relationship between surface area to volume ratio and metabolic rate

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

Changes to body shape and the development of systems as adaptations that facilitate exchange as this ratio reduces.

Development of knowledge of why larger organisms have specialised surfaces and mass transport systems, or particular body shapes

A zoologist investigated the relationship between body mass and rate of oxygen uptake in four species of mammal. The results are shown in the graph.The scale for plotting body mass is a logarithmic scale. Explain why a

logarithmic scale was used to plot body mass.

Large range of values so can fit on graph.

Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between body mass and oxygen

uptake shown in the graph

Smaller animals have larger surface area to volume ratio compared to larger animals, leading to increased heat loss, which in turn requires higher oxygen uptake to maintain body temperature.

A zoologist investigated the relationship between body mass and rate of oxygen uptake in four species of mammal. The results are shown in the graph. The zoologist measured oxygen uptake per gram of body mass. Explain why he

measured oxygen uptake per gram of body mass.

Enables comparison as animals differ in size/mass.

Why don't large multi-cellular organisms just use diffusion to transport substances?

The immediate environment of cells is some form of tissue fluid. Most cells are too far away from exchange surfaces, and from each other.

Function of mass transport

Maintains the final diffusion gradients that bring substances to and from the cell membranes of individual cells.

Adult toads spend most of their time on land but lay their eggs in water. These eggs hatch into tadpoles, which live in water and develop into adults. The tadpoles are much smaller than adult toads. Use this information to explain why the tadpoles are affected more rapidly by pesticides in water than adult toads.

As tadpoles are smaller they will have a large surface area to volume ratio. This results in rapid diffusion because they have a shorter diffusion pathway.

The body of a flatworm is adapted for efficient gas exchange between the water and the cells inside the body. Using the diagram, explain how two features of the flatworm's body allow efficient gas exchange.

Thin, flat body with a short diffusion pathway.

Thin, flat body with a large surface area-to-volume ratio.

The elephant is a very large animal. It has adaptations to increase heat loss from its body surface. A mouse is a very small animal and it has adaptations to reduce heat

loss from its body surface. Explain why these animals have different adaptations for heat loss.

They have a smaller SA-to-volume ratio. So they generate more heat