3.1 Surface area to volume ratio

What is the abbreviation for the ratio between an organism's surface area and its volume?

SA:V (Surface Area to Volume Ratio).

What is the general trend between an organism's size and its SA:V?

As size increases, SA:V decreases.

What is the formula for calculating SA:V?

Surface Area ÷ Volume.

Name two shapes or structural features that can increase an organism's SA:V.

More thin, flat, folded, or elongated structures increase SA:V.

A cube has sides of 2 cm. What is its volume?

2×2×2=8 cm3.

A cube has sides of 2 cm. What is its total surface area?

2×2×6=24 cm2

Using the answers from the previous two cards, what is this cube's SA:V?

24:8=∗∗3:1∗∗.

Why might calculating SA:mass be better than SA:V for some organisms?

It is easier / more accurate for organisms with irregular shapes.

What is the definition of metabolic rate?

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

What common indirect method is used to measure metabolic rate, and why?

• Method: Measure oxygen uptake.

• Reason: Oxygen is used in aerobic respiration to make ATP for energy release.

Why do smaller organisms (with a high SA:V) typically have a higher metabolic rate?

• They have a higher rate of heat loss per unit body mass.

• Therefore, they need a higher rate of respiration to release enough heat to maintain a constant body temperature.

What is the first main adaptation that helps larger organisms (with a lower SA:V) overcome exchange challenges?

• Changes to body shape (e.g., becoming long or thin).

• This increases SA:V and reduces the diffusion distance/pathway.

What is the second main adaptation that helps larger organisms with exchange?

• The development of specialised exchange surfaces/organs (e.g., lungs, gills).

• These increase internal SA:V, reduce diffusion distance, and maintain a concentration gradient (e.g., via ventilation or blood supply).