Animals must keep their cells within a temperature range where enzymes, membranes, and muscles work properly. Ectotherms and endotherms solve this problem in different ways. Ectotherms, such as lizards, frogs, and many fish, rely mostly on heat from the environment.
Endotherms, such as birds and mammals, produce most of their body heat through metabolism.
Key Facts
- Ectotherms gain most body heat from external sources such as sunlight, warm rocks, water, or air.
- Endotherms generate most body heat internally through cellular respiration and metabolism.
- Metabolic rate can be compared with energy use: higher metabolic rate means more food or stored fuel is needed per unit time.
- Heat exchange can occur by conduction, convection, radiation, and evaporation.
- A simple heat balance idea is heat gained minus heat lost = change in body heat.
- Q = mcΔT estimates heat needed to change body temperature, where Q is heat energy, m is mass, c is specific heat, and ΔT is temperature change.
Vocabulary
- Ectotherm
- An animal that depends mainly on external heat sources to regulate its body temperature.
- Endotherm
- An animal that produces most of its body heat internally through metabolic activity.
- Thermoregulation
- The process of maintaining body temperature within a useful range for survival and function.
- Metabolic rate
- The rate at which an organism uses energy through chemical reactions in its cells.
- Behavioral thermoregulation
- Temperature control through actions such as basking, seeking shade, burrowing, huddling, or changing posture.
Common Mistakes to Avoid
- Saying ectotherms are cold-blooded means their blood is always cold. This is wrong because a basking lizard can have a warm body temperature when its environment provides enough heat.
- Assuming endotherms do not use behavior to regulate temperature. This is wrong because mammals and birds still seek shade, huddle, pant, sweat, or change activity times to control heat exchange.
- Thinking endotherms are always better adapted than ectotherms. This is wrong because ectotherms often need much less food and can survive well in environments where energy is limited.
- Confusing body temperature with environmental temperature. This is wrong because endotherms can keep body temperature relatively stable in changing environments, while ectotherms may warm or cool with their surroundings.
Practice Questions
- 1 A 0.20 kg lizard warms from 18°C to 32°C while basking. If its average specific heat is 3500 J/(kg°C), how much heat energy is needed? Use Q = mcΔT.
- 2 A small mammal uses 48 kJ of energy in 6 hours while resting. What is its average energy use per hour in kJ/h? If a lizard of similar mass uses 8 kJ in 6 hours, how many times greater is the mammal's energy use per hour?
- 3 A desert lizard moves onto a sunlit rock in the morning, hides under a shrub at midday, and returns to the rock in late afternoon. Explain how each behavior helps regulate body temperature and why this strategy fits an ectotherm.