Animals have some amazing adaptations that help them live in even the most hostile environments. Consider camels, for instance. They can thrive in some of the hottest and driest places on Earth. Their legs don’t get burned when they kneel on hot sand due to thick leathery patches on their knees. They can survive for an entire week without water but, at the same time, they can drink 32 gallons of water at once. Their body temperature ranges from 93 °F to 107 °F, so they don’t need to sweat very often and can conserve water this way. The spongy bones in their noses absorb any excess moisture to keep every drop of water in, so the air they breathe out is dry air. In addition to camels, other animals’ adaptations are equally remarkable. How do they do it? Chemistry helps!
Warm-blooded or cold-blooded?
The most important adaptation is how animals regulate their body temperature. Animals can be either warm-blooded or cold-blooded.
Warm-blooded animals, which are mostly birds and mammals, need to maintain a relatively constant body temperature or they would suffer dire consequences. It doesn’t matter what the outside temperature is—they must maintain the same internal temperature. For us, the commonly accepted average body temperature is 98.6 °F (even though it may vary among individuals). Most other mammals range from 97 °F to 103 °F; birds have an average body temperature of 105 °F.
Cold-blooded animals do not maintain a constant body temperature. They get their heat from the outside environment, so their body temperature fluctuates, based on external temperatures. If it is 50 °F outside, their body temperature will eventually drop to 50 °F, as well. If it rises to 100 °F, their body temperature will reach 100 °F. Most of the rest of the animal kingdom—except birds and mammals—are cold-blooded.
In most instances, the size and shape of an organism dictate whether it will be warm-blooded or cold-blooded. Think about some large animals—elephants, whales, and walruses. Their volume is so large that relying on the outside environment to heat them up would be inefficient and would slow their response times, putting their survival at risk. For that reason, nearly all large animals are warm-blooded.
What about all the birds and mammals that are not large, such as mice and sparrows? The other factor—body shape—comes into play here. Small warm-blooded animals tend to have a rounded shape, which ensures that the interior of an organism stays warm the longest time possible. Most cold-blooded organisms have either an elongated or a flat shape. If you look at a typical fish, their bodies tend to be flat when viewed head-on from the front. Snakes, lizards, and worms tend to be long and slender. These shapes ensure they can heat up and cool down rapidly.
Within a given species, animals tend to be larger in colder climates and smaller in warmer climates, an observation known as Bergmann’s rule. For example, whitetail deer in the southern part of the United States tend to have a smaller body size and less overall mass than whitetail deer in the far northern states.
There are exceptions but, overall, this rule holds true, for the following reason: As the volume of an object decreases, the ratio of its surface area to its volume increases. In other words, the smaller an animal is, the higher the surface area-to-volume ratio. These animals lose heat relatively quickly and cool down faster, so they are more likely to be found in warmer climates. Larger animals, on the other hand, have lower surface area-to-volume ratios and lose heat more slowly, so and they are more likely to be found in colder climates.
Warm-blooded animals require a lot of energy to maintain a constant body temperature. Mammals and birds require much more food and energy than do cold-blooded animals of the same weight. This is because in warm-blooded animals, the heat they lose is proportional to the surface area of their bodies, while the heat they produce is proportional to their mass. This means that larger warm-blooded animals can generate more heat than they lose and they can keep their body temperatures stable more easily. Smaller warm-blooded animals lose heat more quickly. So, it is easier to stay warm by being larger. Warm-blooded animals cannot be too small; otherwise, they will lose heat faster than they can produce it.
This energy produced by warm-blooded animals mostly comes from food. Food represents stored chemical energy (potential energy), which is converted into other forms of energy within the body when the food is metabolized. Metabolism refers to the all of a body’s chemical reactions.
The metabolism of food within the body is often referred to as internal combustion, since the same byproducts are generated as during a typical combustion reaction—carbon dioxide and water. And like combustion reactions, metabolic reactions tend to be exothermic, producing heat.
For a warm-blooded animal, food is not just a luxury—it is a matter of life and death. If food is not available for energy, the body’s fat is burned. Once fat reserves are used up, death is imminent if a food source is not found. The smaller the warm-blooded animal, the more it must eat—relative to its body size—to keep its internal furnace stoked. That’s why most songbirds fly south for the winter.
On the other hand, cold-blooded animals require less energy to survive than warm-blooded animals do, because much of the energy that drives their metabolism comes from their surroundings. It is common to see turtles basking in the sun on rocks and logs. They are not trying to get a suntan, but rather are revving up their metabolism. The sun gives them an energy boost. Muscle activity in cold-blooded animals depends on chemical reactions, which run quickly when it is hot and slowly when it is cold (because the reacting molecules move faster when temperature increases).
Some reptiles, such as the python, can go a year without eating, because they do not use food to produce body heat. And if they lie still, they use little energy, so they can afford to eat little.
Cold-blooded animals have a disadvantage compared to warm-blooded animals: There is a certain temperature below which their metabolism just won’t work. The reason is that all chemical reactions slow down as the temperature is lowered, so at low temperatures, all the chemical reactions in an organism slow down.
You may notice that few cold-blooded animals are active in the winter, and the farther north you go, the rarer they become. By contrast, warm-blooded animals are present in a wider variety of environments and for a longer part of the year than cold-blooded animals.
For warm-blooded animals that don’t migrate, one way to survive the winter is to sleep through it. Hibernation is a great strategy that enables animals to conserve energy when food is scarce. During hibernation, body temperature drops, breathing and heart rate slows, and most of the body’s metabolic functions are put on hold in a state of quasi-suspended animation.
It is almost as if the warm-blooded animal becomes cold-blooded, as its body temperature drops considerably. But they are still alive, and they live off their fat reserves. Hibernation for extended periods of time is only accomplished by those animals that can store a great deal of body fat, such as bears, groundhogs, and chipmunks. A black bear loses 15%–30% of its weight while hibernating.
Cold-blooded animals hibernate, too. But they need to store less fat than warm-blooded animals because they require less energy. Turtles and frogs bury themselves in mud under lakes and ponds for up to six months at a time, and for all practical purposes, they appear dead. There are no external signs of life.
When many cold-blooded animals hibernate, something interesting happens at the cellular level. The fluid around the cells, but not in the cells, is frozen solid. As water freezes outside the cell, water from within the cell is drawn out through osmosis. Osmosis is a process in which water moves across a semipermeable membrane—in this case, the cell membrane—from an area of low solute concentration to an area of high solute concentration.