A Level Biology Practice Exam

What is callose specifically characterized as?

1. A lipid with high energy content

2. A polysaccharide with specific β linkages

3. A type of protein found in plant cells

4. A nitrogenous base important for RNA

The correct answer is: A polysaccharide with specific β linkages

Callose is specifically characterized as a polysaccharide composed of β-glucan chains that are linked together through specific β-glycosidic linkages. This unique structure allows callose to play important roles in plant biology, particularly in response to injury or stress. It serves as a protective polymer that can be synthesized at sites of wounding to form a callus and is also involved in cell wall modification. The other options mischaracterize the nature of callose. It is not a lipid, so it does not have high energy content or play a role typical of lipids. Also, it is not a protein, meaning it doesn't contribute to structural or enzymatic functions that proteins do, nor is it a nitrogenous base that is essential for the formation of RNA. Hence, the characterization of callose as a polysaccharide with specific β linkages accurately reflects its biochemical nature and functional significance in plants.