Final answer:
Among the four major biological macromolecules, lipids are the most energy-dense, containing the most significant amount of energy per mole, primarily due to their long hydrocarbon chains. Nucleic acids, in contrast, are the least energy-dense as their functions are focused on genetic information storage and transfer.
Step-by-step explanation:
Energy Dense Macromolecules
Biological macromolecules are essential for life and are composed of smaller organic molecules. Among the four major classes - carbohydrates, lipids, proteins, and nucleic acids - lipids contain the most energy per mole, thus making them the most energy-dense macromolecules. Carbohydrates, like sugars and starches, have a general formula where the ratio of carbon to hydrogen to oxygen is 1:2:1 and primarily serve as short-term energy storage and structural support. Proteins, which are involved in a wide variety of cellular functions, can also provide energy but are especially important for building cellular components. Nucleic acids, such as DNA and RNA, store and transmit genetic information but contain less energy compared to lipids and carbohydrates.
When comparing macromolecules in terms of their energy density, lipids stand out because they have a greater amount of energy per gram than the other types of macromolecules. This is partly due to their structure, which contains long chains of hydrocarbons that store significant amounts of energy. Hence, when metabolized, lipids provide a large amount of free energy essential for various biological functions, including long-term energy storage, insulation, and protection.
In answer to the student's question, nucleic acids are the least energy-dense of the macromolecules, as their primary functions are information storage and transfer rather than serving as a primary fuel source for the cell.