3.3.1 Surface area to volume ratio

Question 1

What happens to the surface area to volume ratio as the size of an organism increases?

Answer 1

As the size of an organism increases its surface area to volume ratio decreases.

Question 2

Why do smaller organisms need a higher metabolic rate?

Answer 2

Smaller organisms lose heat more rapidly due to a higher surface area to volume ratio requiring a higher metabolic rate to generate sufficient heat and maintain body temperature.

Question 3

What is the significance of surface area to volume ratio in gas exchange?

Answer 3

A larger surface area to volume ratio allows more efficient gas exchange as diffusion occurs more rapidly across the surface.

Question 4

How do larger organisms overcome the limitations of a small surface area to volume ratio?

Answer 4

Larger organisms develop specialized exchange surfaces (e.g. lungs gills) and transport systems (e.g. circulatory system) to increase the efficiency of substance exchange.

Question 5

Why do animals in cold environments tend to have compact body shapes?

Answer 5

A compact body shape reduces the surface area to volume ratio minimizing heat loss and conserving energy.

Question 6

How does body shape affect heat exchange in hot environments?

Answer 6

Animals in hot environments often have elongated or flattened body shapes to increase surface area to volume ratio facilitating heat loss.

Question 7

Why is a high surface area to volume ratio advantageous for single-celled organisms?

Answer 7

A high surface area to volume ratio allows single-celled organisms to efficiently exchange gases and nutrients directly with their environment via diffusion.

Question 8

What adaptations do organisms have to maximize surface area for exchange?

Answer 8

Organisms develop adaptations such as flattened shapes (e.g. leaves) folded surfaces (e.g. villi in intestines) or branching structures (e.g. alveoli in lungs) to maximize surface area for exchange.

Question 9

How is the metabolic rate related to surface area to volume ratio?

Answer 9

Organisms with a higher surface area to volume ratio (e.g. smaller organisms) have a higher metabolic rate to compensate for greater heat and energy loss.

Question 10

Why do larger organisms require specialized transport systems?

Answer 10

Larger organisms have a reduced surface area to volume ratio making diffusion alone insufficient to meet the demands for oxygen nutrients and waste removal necessitating specialized transport systems.

Question 11

Explain the advantage for larger animals of having a specialised system
that facilitates oxygen uptake. (3)

Answer 11

1. Large(r) organisms have a small(er) surface area:volume (ratio);
   OR
   Small(er) organisms have a large(r) surface area:volume (ratio);
2. Overcomes long diffusion pathway
   OR
   Faster diffusion;

Accept short diffusion pathway
Accept for ‘faster’, more

Question 12

Use your knowledge of surface area to volume ratio to explain the higher
metabolic rate of a mouse compared to a horse. (3)

Answer 12

Mouse

1. (Smaller so) larger surface area to volume ratio;

Accept larger SA:V.
Must be comparative.

2. More/faster heat loss (per gram/in relation to body size);

Ignore heat lost more easily/readily.
Must be comparative.

3. (Faster rate of) respiration/metabolism releases heat;
   Accept respiration/metabolism replaces heat.

Reject produce/generate heat/energy.

Question 13

Describe the relationship between size and surface area to volume ratio of
organisms.

Answer 13

As size increases, ratio (of surface area to volume) decreases;

Accept converse.
Comparison required, e.g., smaller organisms have
a larger ratio

Question 14

Explain why oxygen uptake is a measure of metabolic rate in organisms.

Answer 14

(Oxygen used in) respiration, which provides energy / ATP;

OR

(Oxygen is used in) respiration, which is a metabolic process /
chemical reaction;

Question 15

Tubifex worms are small, thin animals that live in water. They have no
specialised gas exchange or circulatory system.

Using the information provided, explain how two features of the body of
the tubifex worm allow efficient gas exchange.

Answer 15

1. Thin/small so short diffusion pathway;
   Reject: thin membrane/wall/cells.
2. Flat/long/small/thin so large surface area to volume ratio/surface area
   : volume;
   Accept: small volume to surface area ratio.