Select all that apply Which of the following molecules in food can be used as energy sources by living organisms? \( \square \) proteins \( \square \) carbohydrates \( \square \) fats \( \square \) water \( \square \) molecular oxygen

To determine which molecules in food can be used as energy sources by living organisms, let's analyze each option: 1. **Proteins**: - Proteins can be broken down into amino acids, which can be used for energy, especially when carbohydrates and fats are not available. However, their primary role is in building and repairing tissues rather than serving as a primary energy source. 2. **Carbohydrates**: - Carbohydrates are the body's main source of energy. They are broken down into glucose, which is used in cellular respiration to produce ATP (adenosine triphosphate), the energy currency of the cell. 3. **Fats**: - Fats (lipids) are also a significant source of energy. They are broken down into fatty acids and glycerol, which can be used in cellular respiration to generate ATP. 4. **Water**: - Water is essential for life and plays a critical role in various biological processes, but it does not provide energy. 5. **Molecular oxygen**: - Oxygen is crucial for aerobic respiration, allowing organisms to convert glucose and fats into energy. However, oxygen itself is not an energy source; it is a reactant in the process of energy production. Based on this analysis, the molecules that can be used as energy sources by living organisms are: - \( \square \) proteins - \( \square \) carbohydrates - \( \square \) fats So, the correct selections are proteins, carbohydrates, and fats.