Animals can be warm-blooded or cold-blooded. 

What are warm-blooded animals?

Warm-blooded animals are able to maintain a nearly constant body temperature regardless of the temperature of the environment. Usually warm-blooded animals internal body temperature remains constant between 35-40°C.

Mammals and birds are warm-blooded animals, they have complex organ systems and strong immune systems. When the temperature of the environment is cold, warm-blooded animals are able to generate heat from the energy in the food they consume, and they are able to maintain heat using the fat on their bodies. When the temperature of the environment is hot, warm-blooded animals are able to cool down by sweating. Any environmental changes don’t have an effect on metabolic rates. 

A lion is a warm-blooded animal.

A polar bear is a warm-blooded animal.

What are cold-blooded animals?

Cold-blooded animals are not able to maintain a constant internal body temperature. Their temperature changes according to the temperature of the environment; therefore, these animals are unable to survive in extreme temperatures. So in warm weather, they will be warm, and in cold weather, they will be cold. Cold-blooded rely on external sources to regulate heat including the sun and heat from the surrounding environment. This can include changing colours, stretching in the sun, etc. Reptiles, amphibians, fish, insects, and other invertebrates are groups of cold-blooded animals. The metabolic rates of cold-blooded animals depend on the environmental temperature. Cold-blooded animals can protect themselves from extreme temperatures by resting for long periods of time. This includes hibernating during the winter and aestivating during the summer. Body fat is not essential for cold-blooded animals as it can lead to overheating and, ultimately, death. 

A turtle is a cold-blooded animal.

A turtle is a cold-blooded animal.

How do warm-blooded animals maintain a constant internal body temperature?

Warm-blooded animals are able to regulate a constant body temperature regardless of the surrounding environment’s temperature. They can warm up in cold environments and cool down in warm environments. 

There are two thermoregulatory mechanisms:

• Endothermy 
• Homeothermy 

What is endothermy?

Endothermy is the mechanism by which animals control their internal body temperature in different ways, such as shivering, burning fat, panting, etc. 

The opposite of endothermy is ectothermy – this is the mechanism by which cold-blooded use external sources to obtain or release heat. An easy way to remember the difference is that “endo” means inside, and “ecto” means outside. 

What is homeothermy? 

Homeothermy is the mechanism by which animals control their internal body temperature while the environmental temperature changes. This means the animal’s activities are not reliant on environmental conditions. 

The opposite of homeothermy is heterothermy – this is the mechanism by which an animal’s body temperature changes drastically as it moves from one environment to another. An easy way to remember the difference is that “homeo” means same, and “hetero” means different. 

Warm-blooded animals use a combination of endothermy and homeothermy to control their internal body temperature. Metabolic activities are the main source of control for body temperature, however, there are other factors that a significant role. Examples of structural factors include thick fur and sweat glands. 

In some cases, animals (homeotherms) do not have enough food during the cold environments in winter to aid their metabolic activities. These animals will undergo hibernation. 

How do cold-blooded animals regular their internal body temperature?

There are three types of thermoregulatory mechanisms:

• Ectothermy
• Heterothermy
• Poikilothermy

What is ectothermy?

Ectothermy is the mechanism by which animals use external sources to obtain or release heat. An example of an external source is the sun. This process controls internal body temperature without affecting the animal’s metabolic rate. Therefore, they can survive without food for extended periods of time as they don’t require energy to generate heat.

The opposite of ectothermy is endothermy – this is the mechanism in which warm-blooded animals maintain a constant internal body temperature using metabolic processes which require energy. An easy way to remember the difference is that “endo” means inside, and “ecto” means outside. 

What is heterothermy?

Heterothermy is the mechanism by which an animal’s body temperature changes drastically as it moves from one environment to another. The animal is able to switch from endothermy to ectothermy. This usually occurs in animals with high metabolic rates that decrease their internal body temperature during inactivity periods daily or yearly. This period is often known as metabolic depression. Hibernation is an example of a period of inactivity. During hibernation, an animal’s metabolic rate is lowered; so they stop regulating its internal body temperature. Their body temperature becomes similar to that of the environment, this is why hibernators generally look for places that are not too cold. Heterotherms end up relying on external sources such as the sun or warm places to control their body temperature. 

The opposite of homeothermy is heterothermy – this is the mechanism by which animals control their internal body temperature while the environmental temperature changes. An easy way to remember the difference is that “homeo” means same, and “hetero” means different. 

What is poikilothermy?

Poikilothermy is the mechanism in which the internal body temperature of animals changes as the external environment temperature changes. Therefore, the animal’s activities become reliant on the environment.