* Energy Source: Carbohydrates, particularly sugars like glucose, are the primary energy source for plants (and most living organisms). They are broken down through cellular respiration to produce ATP, the energy currency of cells.

* Structural Support: Carbohydrates like cellulose form the rigid cell walls of plants, providing support and structure. Cell walls help plants maintain their shape, withstand turgor pressure (water pressure), and provide protection.

Other options are incorrect because:

* Proteins: While proteins are essential for various functions in plants, they are not the primary energy source. They primarily serve structural, enzymatic, and signaling roles.

* Lipids (fats): Lipids are important for energy storage, insulation, and membrane structure but don't provide the same structural support as carbohydrates.

* Nucleic acids (DNA and RNA): These molecules carry genetic information and are not involved in energy production or providing structural support.