Final answer:
A macronutrient high in cellulose and water has low energy density because humans cannot digest cellulose, meaning it does not contribute caloric energy. Cellulose is less energy-dense compared to lipids, and contributes to dietary fiber rather than energy intake. Option B is the correct answer.
Step-by-step explanation:
When analyzing a macronutrient high in cellulose and water, it is important to consider the energy density of the macronutrient. Energy density is defined by how concentrated energy is in a substance, typically quantified as energy per unit mass. It is known that carbohydrates and proteins provide around 4 kcal/g, lipids offer about 9 kcal/g, and any substance with around 10 kcal/g or higher is considered to be energy-dense.
Cellulose is a complex carbohydrate that forms the cell walls in plants and some algae, and although it is a crucial part of dietary fiber, it is not digested by humans. The structure of cellulose includes extensive hydrogen bonding, which contributes to its rigidity. As humans cannot digest cellulose, it provides no caloric energy and is therefore considered to have a low energy density.
When examining the energy density in the context of dietary choices and achieving energy homeostasis, cellulose would not contribute to the caloric intake. Foods high in carbohydrates or proteins, like cellulose, are generally less energy-dense compared to those high in lipids. This is particularly relevant in the context of maintaining a balance between the energy consumed and the energy expended in metabolism and physical activity.
Considering these facts, we can conclude that a macronutrient high in cellulose and water has a low energy density. Therefore, the correct option is b. low energy density.