Advanced Placement (AP) Biology Practice Exam

What does metabolism encompass in an organism?

1. All structural functions of the cell

2. The totality of an organism's chemical reactions

3. Only energy-releasing reactions

4. Only energy-consuming reactions

The correct answer is: The totality of an organism's chemical reactions

Metabolism refers to the totality of an organism's chemical reactions, which include all the biochemical processes that occur within cells. This encompasses both catabolic pathways, which break down molecules and release energy, and anabolic pathways, which build up molecules and consume energy. The balance and regulation of these reactions are crucial for maintaining homeostasis and supporting the life processes of the organism. While the other options mention important aspects of cellular functions, they do not capture the full breadth of metabolism. For instance, metabolism is not limited to just structural functions or either energy-releasing or energy-consuming reactions alone; rather, it integrates all the chemical reactions needed for growth, reproduction, and cellular maintenance. Understanding metabolism in this comprehensive way is essential to grasp the energetic and material exchanges that sustain life.