Which of the following provides the most readily available source of energy for living cells?

• A. Glucose
• B. Nucleic acids
• C. Triglycerides
• D. Proteins

Answer: (A)

Verified step by step guidance

1. Understand the role of energy sources in living cells: Living cells require energy to perform various functions such as growth, repair, and maintaining homeostasis. This energy is primarily derived from macromolecules through metabolic processes.
2. Review the primary macromolecules listed in the problem: Glucose, nucleic acids, triglycerides, and proteins. Each of these has a distinct role in cellular function, but not all are primarily used as an immediate energy source.
3. Analyze glucose as an energy source: Glucose is a monosaccharide and serves as the most readily available source of energy for cells. It is metabolized through glycolysis, producing ATP, the energy currency of the cell. The chemical formula for glucose is $C_6{H}_{12}{O}_6$.
4. Evaluate nucleic acids, triglycerides, and proteins: Nucleic acids (DNA and RNA) are primarily involved in genetic information storage and transfer, not energy production. Triglycerides are long-term energy storage molecules, broken down into fatty acids and glycerol during lipolysis, but they are not as readily available as glucose. Proteins are primarily used for structural and functional roles (e.g., enzymes) and are not the primary energy source unless under extreme conditions.
5. Conclude that glucose is the most readily available energy source: Glucose is rapidly metabolized to produce ATP through glycolysis and subsequent pathways like the citric acid cycle and oxidative phosphorylation, making it the preferred immediate energy source for living cells.