What NEET Asks
- Expect direct questions on definitions and examples of mono-, di-, and polysaccharides.
- Classification based on hydrolysis and distinguishing features are frequently tested.
- This topic typically contributes 1-2 questions, carrying 4-8 marks in the Biomolecules section.
Key Points
- Carbohydrates: Polyhydroxy aldehydes or ketones, or compounds that produce them upon hydrolysis. They are generally represented by the formula Cx(H2O)y.
- Monosaccharides: Simplest carbohydrates; cannot be hydrolyzed further into smaller units. Examples: Glucose, Fructose, Ribose.
- Disaccharides: Yield two monosaccharide units upon hydrolysis. Examples: Sucrose (Glucose + Fructose), Maltose (Glucose + Glucose), Lactose (Glucose + Galactose).
- Polysaccharides: Yield a large number of monosaccharide units upon hydrolysis (>10 units). Examples: Starch, Cellulose, Glycogen.
- Sugars are crystalline, soluble in water, and sweet in taste (mono and disaccharides). Non-sugars are amorphous, insoluble, and tasteless (polysaccharides).
Must-Know Formula / Reaction
- General formula for carbohydrates: Cx(H2O)y
C: Total number of carbon atoms.(H2O): Represents units of water, though not all compounds matching this formula are carbohydrates.
- Disaccharide Hydrolysis: Sucrose + H₂O Glucose + Fructose
Common Mistakes
- Students often assume any compound fitting Cx(H2O)y is a carbohydrate (e.g., acetic acid, formaldehyde). Remember the 'polyhydroxy aldehyde/ketone' part of the definition.
- Don't confuse reducing/non-reducing properties with the classification based on hydrolysis.
- Students often forget specific examples for each class (e.g., cellulose is a polysaccharide, not a disaccharide).
Rapid Revision
Carbohydrates are polyhydroxy carbonyl compounds. Classify by hydrolysis: Monosaccharides (no hydrolysis), Disaccharides (2 units), Polysaccharides (>10 units). Key examples: Glucose (mono), Sucrose (di), Starch (poly). Remember the general formula Cx(H2O)y, but also its limitations.