1. Thermoregulation The maintenance of body temperature within a range that enables cells to function efficiently

2. Heat Exchange - Ectotherms Ectotherms depend on air temperature to regulate metabolic rates. Therefore their activity is partially regulated by the environment Reptiles Amphibians Invertebrates Most Fish “Cold-Blooded” They develop behavioral adaptations to regulate body temperature

3. Heat Exchange - Endotherms Endotherms are able to maintain a constant body temperature regardless of their surroundings. Adjust to decreases in environmental temperature by increasing the rate of cellular respiration to generate heat. Mammals and Birds 37°C is normal body temperature Hypothalamus: The human “thermostat”

4. Response to Heat Response to Cold

5. Stimulus-Responsefor Thermoregulation

6. Activity

7. Mammalian Diving Reflex What happens to the heart rate when a person falls into cold water? Test the diving reflex with this activity, and see how your body responds.

8. Procedure Measure your resting pulse rate in beats per min. Have your partner place two fingers on your wrist and count your heartbeat for 15 s. Multiply this number by four and record your results. Now hold your breath and submerge your face in the pan of cold water for 15 s. Before you start, explain what you think will happen to your pulse as a result of this test. While your face is in the water, have your partner measure your pulse for 15 s. Multiply this number by four and record your results. Switch roles and repeat the procedure.

9. What happens to your pulse when your face is immersed in cold water? Why do you think this happened? How might this response help a person who has fallen into very cold water?