3.3.1 Surface area to volume ratio

What is the relationship between the size of an organism and its surface area to volume ratio?

• As the size of an organism increases, the surface area to volume ratio increases.

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

• The surface area to volume ratio remains constant regardless of the size of the organism.

• The surface area to volume ratio is not related to the size of an organism.

Answer explanation

As an organism increases in size, its volume grows faster than its surface area. This results in a lower surface area to volume ratio, which is crucial for processes like gas exchange and nutrient absorption.

Why do larger organisms develop specialised systems for exchange?

• To increase their surface area to volume ratio.

• To decrease their metabolic rate.

• To facilitate efficient exchange of materials as their surface area to volume ratio decreases.

• To maintain a constant body temperature.

Answer explanation

Larger organisms have a lower surface area to volume ratio, making it difficult to exchange materials efficiently. Specialised systems, like circulatory and respiratory systems, enhance this exchange to meet their metabolic needs.

Which of the following is an adaptation that helps larger organisms manage their reduced surface area to volume ratio?

• Developing a thicker skin.

• Having a flattened body shape.

• Reducing their metabolic rate.

• Increasing their body temperature.

Answer explanation

Having a flattened body shape increases surface area relative to volume, allowing larger organisms to better manage heat and nutrient exchange, which is crucial due to their reduced surface area to volume ratio.

How does a reduced surface area to volume ratio affect the metabolic rate of an organism?

• It increases the metabolic rate.

• It decreases the metabolic rate.

• It has no effect on the metabolic rate.

• It causes the metabolic rate to fluctuate.

Answer explanation

A reduced surface area to volume ratio means less area for heat and waste exchange, leading to increased metabolic activity to maintain homeostasis, thus increasing the metabolic rate.

Which of the following structures in larger organisms is an adaptation to improve exchange efficiency?

• Thick fur.

• Large ears.

• Small eyes.

• Short limbs.

Answer explanation

Large ears are an adaptation that increases surface area for heat dissipation, improving exchange efficiency in larger organisms. This is particularly beneficial in hot environments, unlike the other options which do not enhance exchange.

What is the primary reason smaller organisms do not require complex systems for exchange?

• They have a higher surface area to volume ratio.

• They have a lower metabolic rate.

• They live in colder environments.

• They are less active.

Answer explanation

Smaller organisms have a higher surface area to volume ratio, allowing for efficient exchange of materials directly through their surfaces, negating the need for complex systems like those found in larger organisms.

Which of the following is a consequence of a low surface area to volume ratio in large organisms?

• Increased heat loss.

• Decreased nutrient absorption.

• Increased metabolic waste accumulation.

• Decreased oxygen uptake.

Answer explanation

A low surface area to volume ratio in large organisms leads to decreased oxygen uptake, as there is less surface area available for gas exchange relative to their volume, impacting respiration efficiency.

How do gills in fish exemplify an adaptation to surface area to volume ratio challenges?

• They increase the volume of the fish.

• They provide a large surface area for gas exchange.

• They decrease the surface area of the fish.

• They reduce the metabolic rate of the fish.

Answer explanation

Gills in fish provide a large surface area for gas exchange, allowing efficient oxygen uptake and carbon dioxide removal. This adaptation addresses the challenges of maintaining a suitable surface area to volume ratio in aquatic environments.

Which of the following is true about the metabolic rate of small organisms compared to large organisms?

• Small organisms have a lower metabolic rate per unit of mass.

• Small organisms have a higher metabolic rate per unit of mass.

• Small organisms have the same metabolic rate as large organisms.

• Metabolic rate is not related to organism size.

Answer explanation

Small organisms have a higher metabolic rate per unit of body mass because they have a larger surface area relative to their volume, leading to greater energy expenditure per unit mass compared to larger organisms.

What role does the circulatory system play in larger organisms with respect to surface area to volume ratio?

• It decreases the surface area to volume ratio.

• It helps distribute nutrients and gases efficiently throughout the body.

• It increases the metabolic rate.

• It reduces the need for oxygen.

Answer explanation

The circulatory system is crucial for larger organisms as it efficiently distributes nutrients and gases throughout the body, compensating for the lower surface area to volume ratio that limits direct diffusion.