Advanced Placement (AP) Biology Practice Exam

What is respiration primarily responsible for?

1. Conversion of light energy into chemical energy

2. Breaking down glucose for energy

3. Synthesis of carbohydrates

4. Absorption of nutrients from the soil

The correct answer is: Breaking down glucose for energy

Respiration is primarily responsible for breaking down glucose for energy, which is a crucial process for all living organisms. During cellular respiration, glucose is metabolized in a series of biochemical reactions that produce adenosine triphosphate (ATP), the energy currency of the cell. This process involves glycolysis, the citric acid cycle, and oxidative phosphorylation, where glucose is ultimately converted into carbon dioxide and water, releasing energy in the form of ATP. The other options describe processes that occur in living systems, but they do not accurately characterize respiration. For instance, the conversion of light energy into chemical energy specifically refers to photosynthesis, which occurs in plants and some other organisms. The synthesis of carbohydrates is related to photosynthesis as well, where plants create glucose using sunlight, carbon dioxide, and water. Lastly, the absorption of nutrients from the soil is a function of the root system in plants and is essential for nutrient acquisition but is separate from the energy production role of respiration.