Control of the Internal Environment for AP Biology (page 2)

By — McGraw-Hill Professional
Updated on Oct 24, 2011


A fairly constant body temperature is important for many living organisms. The process by which this temperature is maintained is known as thermoregulation. A major organ involved in thermoregulation is the skin, which also plays a role in excretion through sweating. Four major thermoregulatory processes are conduction, convection, evaporation, and radiation. Conduction is the process by which heat moves from a place of higher temperature to a place of lower temperature. For example, let's say that two people are sleeping in the same bed, and that person A is cold all the time. Person A would not make it through the night if it were not for this process. Since person B tends to be warmer than person A, person A takes advantage of conduction by pulling the heat from person B's body to hers. Convection is heat transfer caused by airflow. Thinking about my baseline warmth (similar to that of person B), if it were not for my air conditioner in the summer, I would probably not be here today to write this book. But we curse convection in the winter as the cold wind removes heat from our bodies, making it feel that much colder outside. Evaporation is the process by which water leaves our bodies in the form of water vapor: sweat. Why do humid days feel so much warmer than nonhumid days? Because humidity increases the amount of water in the air, decreasing the driving force for water to leave our bodies. Radiation is the loss of heat through ejection of electromagnetic waves.

Before moving on to the nervous system, I must mention two more terms: endotherm and ectotherm. An endotherm is an organism whose body temperature is not dramatically affected by the surrounding temperature. We humans are endothermic creatures. Sure, a cold day can feel really cold, but at least it does not dramatically lower the human body temperature. Ectothermic animals are organisms whose body temperatures are affected by the surrounding temperature. Fish, reptiles, and amphibians are good examples of ectothermic organisms.

Practice problems for these concepts can be found at: Human Physiology Review Questions for AP Biology

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