Advanced Placement (AP) Biology Practice Exam

Which macromolecule is primarily responsible for structural support in plant cells?

1. Proteins

2. Carbohydrates

3. Nucleic acids

4. Lipids

The correct answer is: Carbohydrates

The correct answer is carbohydrates, as they play a crucial role in providing structural support in plant cells. The primary carbohydrate involved in this function is cellulose, which is a major component of the plant cell wall. Cellulose is a polysaccharide composed of long chains of glucose units linked by beta-1,4-glycosidic bonds. This structure gives plant cells rigidity and strength, allowing them to maintain their shape and resist external pressures. In addition to cellulose, other polysaccharides such as hemicellulose and pectin also contribute to the structural integrity of plant cell walls. These carbohydrates work together to form a robust framework that supports the plant's overall structure and plays a key role in processes such as growth and transport of water and nutrients. While proteins, nucleic acids, and lipids have their own important functions within the cell, they do not primarily serve the structural support role that carbohydrates, specifically in the form of cellulose, provide in plant cells.