Concept Check 40

If you monitored energy allocation in the penguin in Figure 40.20 for just a few months, the ¨growth¨ category might now be a significant part of the pie chart, even though adult penguins don't change in size from year to year. What limitation in such energy budget studies does this lead you to consider?

Although penguins do not grow as adults, they increase and decrease in size as they repeatedly form and use energy stores. A significant amount of energy might be stored in fat during part of the year but be missing from the pie chart because it is used later in the year.

Under what temperature conditions would it benefit a jackrabbit to flatten its ears against its body? Explain.

By flattening its ears against its body, the jackrabbit can reduce the total surface area of its body and hence the amount of heat absorbed when environmental temperatures are high, or the amount of heat lost when environmental temperatures are low.

What properties are shared by all types of epithelia?

Epithelial cells line a surface, are tightly packed, are situated on top of a basal lamina, and form an active and protective interface with the external environment.

Which animal must eat a larger proportion of its weight in food each day: a house cat or an African lion caged in a zoo?

The house cat; the smaller an animal is, the higher its metabolic rate and its demand for food per unit of body mass are.

Flowers differ in how much sunlight they absorb. Why might this matter to a hummingbird seeking nectar on a cool morning?

The hummingbird, being a very small endotherm, has a very high metabolic rate. If by absorbing sunlight certain flowers warm their nectar, a hummingbird feeding on these flowers is saved the metabolic expense of warming the nectar to its body temperature.

Suppose at the end of hard run on a hot day you find out that there are no drinks left in the cooler. If, out of desperation, you dunk your head into the cooler, how might the ice-cold water affect the rate at which your body temperature returns to normal?

The ice water would cool tissues in your head, including blood that would then circulate throughout the body. This effect would accelerate the return to a normal body temperature. If, however, the ice water reached the eardrum and cooled the hypothalamic thermostat, the perceived drop in temperature would inhibit sweating and blood vessel dilation, slowing cooling elsewhere in the body.

If a mouse and a small lizard of the same mass (both at rest) were placed in experimental chambers under identical environmental conditions, which animal would consume oxygen at a higher rate? Explain.

The mouse would consume oxygen at a higher rate because it is an endotherm and therefore its basal metabolic rate is higher than the ectothermic lizard´s standard metabolic rate.

What mode of heat exchange is involved in ¨wind chill,¨ when moving air feels cooler than still air at the same temperature?

Wind chill involves heat loss through convection.

Suppose you are standing at the edge of a cliff and you suddenly slip-you barely manage to keep your balance to keep from falling. As your heart races, you feel a burst of energy, due in part to a surge of blood into dilated (widened) vessels in your muscles and an upward spike in the level of glucose in your blood. Why might you expect that this ¨fight-or-flight¨ response requires both the nervous system and endocrine system?

You need the nervous system to perceive the danger and provoke a split-second muscular response to keep from falling. The nervous system, however, does not make a direct connection with blood vessels or liver cells. Instead, the nervous system triggers the release of a hormone (called epinephrine or adrenaline) by the endocrine system, bringing about a change in these tissues in just a few seconds.