3.1 Surface area to volume ratio

Describe the relationship between the size and structure of an organism and its sa:v

• as size increases, SA:V tends to decrease

• More thin /flat/ folded/ elongated structures increase SA:V

How is SA:V calculated?

Divide surface area (size length x side width x no. sides) by volume ( length x width x depth)

Suggest an advantage of calculating SA:mass for organisms instead of SA:V

Easier/ quicker to find/ more accurate because of irregular shapes

What is metabolic rate?

The amount of energy used up by an organism within a given period of time.

Suggest how metabolic rate can be measured.

by oxygen uptake → as used in aerobic respiration to make ATP for energy release

Explain the relationship between SA:V and metabolic rate.

As SA:V increases (smaller organisms), metabolic rate increases because:

• Rate of heat loss per unit body mass increases

• So organisms need a higher rate of respiration

• To release enough heat to maintain a constant body temp ie. replace heat lost

Explain the adaptations that facilitate exchange as SA:V reduces in larger organisms.

1. Changes to body shape (eg. long /thin)

• Increases SA:V and overcomes long diffusion distance

2. Development of systems, such as specialised surface for gaseous exchange eg. lungs:

• Increases (internal) SA:V and overcomes long diffusion distance

• Maintain a conc. gradient for diffusion eg. by ventilation/ good blood supply