OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What mechanism helps trap heat when you are cold?

1. Increased sweat production

2. Constricted blood vessels

3. Contracting of erector muscles

4. Lowered metabolic rate

The correct answer is: Contracting of erector muscles

The correct answer is that the contracting of erector muscles helps trap heat when you are cold. When the body experiences cold temperatures, small muscles at the base of hair follicles, known as erector muscles, contract. This contraction causes the hair to stand upright, a response commonly referred to as "goosebumps." This physiological response not only traps a layer of air close to the skin, which provides some insulation, but it also can help in retaining body heat. The uplifted hair creates a slightly thicker layer of air that acts as an insulator, reducing the rate of heat loss from the body. The other options do not contribute effectively to heat retention in the same way. Increased sweat production is primarily a response to overheating, helping to cool the body down. Constricted blood vessels do play a role in reducing blood flow to the skin, thereby minimizing heat loss, but it is the direct action of the erector muscles that specifically serves to trap heat more immediately. A lowered metabolic rate would decrease the body’s internal heat production, which does not help in retaining warmth when cold.