What is anabolism primarily responsible for?

Anabolism is primarily responsible for the process of building larger molecules from smaller ones. This metabolic pathway is essential for growth, repair, and maintenance of tissues in the body. During anabolism, smaller units, such as amino acids or simple sugars, are assembled into complex structures like proteins and carbohydrates. This process requires energy, typically in the form of adenosine triphosphate (ATP), which is why it is often coupled with catabolism, where larger molecules are broken down to release energy for anabolism to occur.

In the context of the other options, breaking down large molecules refers to catabolic processes, which are the opposite of anabolism. Regulating body temperature is a function more related to homeostasis and the body's thermoregulatory mechanisms, while transporting nutrients is primarily associated with the circulatory system and cellular uptake processes. Therefore, the correct answer highlights the constructive aspect of metabolism that is vital for the overall functioning and health of living organisms.