When animals consume more energy than they expend over time, how is the excess energy stored?

When animals consume more energy than they use, the excess energy is primarily stored as fat. This storage occurs because fat provides a highly efficient means of energy storage. When energy intake exceeds energy expenditure, the body converts excess carbohydrates and proteins into fatty acids through a process called lipogenesis. These fatty acids are then combined with glycerol to form triglycerides, which are stored in adipose tissues. This method is advantageous as fat has a much higher energy density than carbohydrates or proteins, allowing for compact storage of energy that can be utilized later when needed, such as during periods of fasting or increased energy demands.

In contrast, while the body also stores energy as glycogen, primarily in the liver and muscles, glycogen stores are limited and can quickly become saturated. Glucose exists in the bloodstream and is utilized for immediate energy needs, but it is not stored directly; instead, it can be converted to glycogen and fat for longer-term storage. Proteins serve more for growth and repair rather than as an energy reserve, and excess protein is not preferentially stored as protein but can be converted into fat as well. Thus, the correct response highlights the body's preference for fat as a long-term energy-storing molecule.