Massachusetts Comprehensive Assessment System (MCAS) Biology Practice Test

What is a primary use of the smaller molecules produced by the digestive system?

1. Creating heat

2. Cellular respiration, repair, and growth

3. Generating energy directly

4. Storage of nutrients

The correct answer is: Cellular respiration, repair, and growth

The smaller molecules produced by the digestive system, such as amino acids, fatty acids, and monosaccharides, primarily serve as building blocks for various biological processes, including cellular respiration, repair, and growth. Once food is broken down in the digestive system, these smaller components are absorbed into the bloodstream and transported to cells throughout the body. In cellular respiration, these molecules undergo metabolic pathways to produce ATP, which is the main energy currency of the cell. Additionally, they are crucial for the synthesis of new cellular structures, supporting tissue repair and growth, especially after injury or during developmental stages. For example, amino acids are used to build proteins, which are necessary for muscle growth and repair. While generating energy directly is an important function, it is not the immediate role of the small molecules themselves; rather, it's the processes they undergo within cellular respiration that yield energy. Similarly, while heat is generated as a byproduct of metabolism, it is not a primary function of the smaller molecules from digestion. The storage of nutrients occurs, but it is typically in the form of glycogen or triglycerides, which is a subsequent function that happens after digestion, rather than the primary use of these smaller molecules right after they are synthesized.