B1.1 Carbohydrates and lipids

The question asks how a glycosidic bond is broken during digestion. Breaking a bond in a polymer to release monomers is the reverse of condensation — this process is called hydrolysis.

Hydrolysis means 'splitting by water'. A water molecule ($H_{2}O$) is added across the covalent bond; the –H attaches to one monomer and the –OH attaches to the other, regenerating the hydroxyl groups that were lost during condensation.

In polysaccharide digestion, enzymes (e.g., amylase) catalyse the addition of water across each glycosidic bond. The result is two free monosaccharides, each with their –OH groups restored.

The correct description is: a water molecule is added across the bond, with –H and –OH attaching to the separated monomers. This is the definition of hydrolysis.

The question asks for the mechanism of glycosidic bond breaking during digestion — we need to identify the correct description of hydrolysis.

Removing water describes condensation (bond formation), not bond breaking. This is the opposite process — eliminate this option.

Enzymes lower activation energy but do not directly donate protons to glycosidic bonds in this manner. This misrepresents how hydrolytic enzymes work — eliminate this option.

This describes no recognised biochemical mechanism. Hydrolysis does not involve replacement of carbon atoms — eliminate this option.

The remaining option — a water molecule is added across the bond, with –H and –OH attaching to the separated monomers — correctly defines hydrolysis and is the answer.

Saturated fatty acids have no C=C double bonds — their chains are straight and pack tightly together. Unsaturated fatty acids have one or more C=C double bonds — each double bond creates a kink in the chain.

Fatty acid X has no double bonds → it is saturated. Fatty acid Y has two double bonds → it is polyunsaturated.

Saturated fatty acids pack tightly due to straight chains → stronger intermolecular forces → higher melting point → solid at 25°C (e.g., butter). Unsaturated fatty acids have kinked chains → cannot pack tightly → lower melting point → liquid at 25°C (e.g., plant oils).

Fatty acid X is saturated and solid; fatty acid Y is unsaturated and liquid. This matches the second option.

We need to correctly classify fatty acids X and Y as saturated or unsaturated, and predict their physical states.

This reverses the correct classification. X has no double bonds, making it saturated (not unsaturated), and Y has two double bonds, making it unsaturated (not saturated). Eliminate.

The classification is correct, but the physical states are reversed. Saturated fatty acids are solid due to tight packing; unsaturated ones are liquid. Eliminate.

X has no double bonds so it cannot be unsaturated. This option is factually incorrect — eliminate.

Fatty acid X is saturated and solid; fatty acid Y is unsaturated and liquid is the only option with correct classification and correct physical states.