Question

Which of the following are true ? A. All the monosaccharides except dihydroxyacetone contain one or more asymmetric carbon atoms.
B. Sucrose is a disaccharide consisting of D-glucose and D-fructose.
C. Sugars capable of reducing cupric ions are called reducing sugars.
D. Starch is the main storage polysaccharide of animal cells.
E. The rigid bacterial cell wall is made up of cellulose.
Choose the correct answer from the options given below :

• A. \(A, C\) only
• B. \(A, B, C\) only
• C. \(A, D\) only
• D. \(E, C\) only

Hint:

Remember:
• Sucrose \(=\) Glucose + Fructose
• Glycogen \(\rightarrow\) Animal storage polysaccharide
• Starch \(\rightarrow\) Plant storage polysaccharide
• Peptidoglycan \(\rightarrow\) Bacterial cell wall \[ \text{Reducing sugars reduce } Cu^{2+} \text{ in Benedict's/Fehling's test} \]

Answer 1

The Correct Option is B

Concept: Carbohydrates include:
• Monosaccharides
• Disaccharides
• Polysaccharides They play important roles in:
• Energy storage
• Structural support
• Cellular metabolism

Step 1: Evaluating statement A. Statement A: \[ \text{All monosaccharides except dihydroxyacetone contain asymmetric carbon atoms} \] This is correct. Dihydroxyacetone is: \[ \text{A ketotriose without a chiral carbon} \] while most other monosaccharides possess one or more asymmetric carbon atoms. Thus: \[ \boxed{A \text{ is correct}} \]

Step 2: Evaluating statement B. Statement B: \[ \text{Sucrose consists of D-glucose and D-fructose} \] This is correct. Sucrose is formed by linkage between: \[ \alpha\text{-D-glucose and }\beta\text{-D-fructose} \] Thus: \[ \boxed{B \text{ is correct}} \]

Step 3: Evaluating statement C. Statement C: \[ \text{Sugars reducing cupric ions are reducing sugars} \] This is correct. Reducing sugars possess free aldehyde or ketone groups capable of reducing: \[ Cu^{2+} \rightarrow Cu^+ \] in Benedict’s or Fehling’s test. Thus: \[ \boxed{C \text{ is correct}} \]

Step 4: Evaluating statement D. Statement D: \[ \text{Starch is the storage polysaccharide of animal cells} \] This is incorrect. In animals, the major storage polysaccharide is: \[ \text{Glycogen} \] while starch is the storage polysaccharide of plants. Thus: \[ \boxed{D \text{ is incorrect}} \]

Step 5: Evaluating statement E. Statement E: \[ \text{Bacterial cell wall is made of cellulose} \] This is incorrect. The bacterial cell wall is primarily composed of: \[ \text{Peptidoglycan (murein)} \] Cellulose is mainly found in plant cell walls. Thus: \[ \boxed{E \text{ is incorrect}} \] Therefore, the true statements are: \[ \boxed{A, B, C} \] Hence, the correct answer is: \[ \boxed{(B)\ A, B, C \text{ only}} \]