Question

Small mammals and birds are rarely found in polar regions. The reason is that

• A. They have a larger surface area relative to their volume
• B. They tend to gain heat very fast
• C. They expand less energy to generate body heat
• D. None of the above

Answer 1

The Correct Option is A

The question asks for the reason why small mammals and birds (which are homeotherms, maintaining a constant internal body temperature) are rarely found in cold polar regions. 

Let's analyze the relationship between body size, heat generation, and heat loss:

• Heat Generation: Metabolic heat production is roughly proportional to the body's volume (or mass). Volume scales with the cube of a linear dimension (L³).
• Heat Loss: Heat is lost to the environment primarily through the body surface. Surface area scales with the square of a linear dimension (L²).
• Surface Area to Volume Ratio (SA/V): The ratio of surface area to volume is proportional to L²/L³ = 1/L. This means that smaller animals have a larger surface area relative to their volume compared to larger animals.

In cold environments like the polar regions:

• Animals continuously lose heat to the colder surroundings.
• A larger surface area relative to volume (high SA/V ratio) facilitates a much faster rate of heat loss.
• Small mammals and birds, having a high SA/V ratio, lose body heat very quickly.
• To compensate for this rapid heat loss and maintain their constant internal body temperature, they must generate a large amount of metabolic heat. This requires a very high metabolic rate and consumes a significant amount of energy (food).
• Sustaining such high energy expenditure is extremely difficult in polar regions, where food availability can be limited.

Now let's evaluate the options:

• They have a larger surface area relative to their volume: This is correct. This high SA/V ratio is the fundamental physical reason for their rapid heat loss, making it energetically expensive to survive in extreme cold.
• They tend to gain heat very fast: Incorrect. In a cold environment, the net flow of heat is outwards (loss). They lose heat fast.
• They expand less energy to generate body heat: Incorrect. Due to rapid heat loss, they must expend more energy per unit mass to generate sufficient body heat.
• None of the above: Incorrect, as the first option is correct.

Therefore, the reason small mammals and birds are rarely found in polar regions is that They have a larger surface area relative to their volume, leading to excessive heat loss.

Answer 2

Small mammals and birds are rarely found in polar regions because they have a larger surface area relative to their volume. This characteristic leads to higher heat loss, which makes it more difficult for them to survive in extremely cold climates. In cold environments, animals with larger surface areas (like small mammals and birds) lose heat quickly, which makes it harder for them to maintain body temperature, unlike larger animals with a more favorable surface area-to-volume ratio.

The correct answer is (A) : They have a larger surface area relative to their volume.