Answer:
The correct answer is : 1. carbohydrate.
Step-by-step explanation:
Cellulose is a major substance present in cell walls of the plants which provides support to the structure of plants. As it is most abundant bio polymer in nature are made up of monomers of glucose molecule joined together by bonds in between specific carbon atoms.
The rigidity of the plant is come from this carbohydrate, cellulose. Lipids, proteins are also component of the plant cell and plays various role in the cell for instance lipid acts as barrier and present in plasma membrane of the plant cell and provide insulation too.
Thus, the correct answer is : 1. carbohydrate.