Final answer:
Whitney was hot and sweaty after running due to an increased metabolic rate from exercise, which produced excess heat, leading to sweating as a means of cooling through evaporation.
Step-by-step explanation:
Whitney went out for a run and after 20 minutes of running she was hot and sweaty. The best biological explanation for this observation is that during exercise, her body's metabolic rate increased. This means her body was consuming more energy, which in turn generated more heat as a byproduct of the metabolic processes in her muscles. As the body is inefficient in converting all the consumed energy into work, a significant amount of this energy is lost as heat. In order to maintain body thermoregulation, which is the balance of heat production and heat loss, her body responded by producing sweat.
Sweat cools the body through evaporation. When sweat evaporates from the skin, it removes a great deal of heat with it, due to the energy required for the water molecules to change from a liquid to a gas. This is the body's primary means of cooling itself down during exercise, as opposed to when at rest, where much less heat is lost through evaporation. Importantly, this cooling effect is more efficient in environments with lower relative humidity because more sweat can evaporate. Lastly, it is crucial for athletes, like Whitney, to replace the water and electrolytes lost in sweat to maintain the body's fluid balance.