Test: Carbohydrates - NEET MCQ

Maltose can be produced from starch by hydrolysis in the presence of the enzyme diastase. It can be broken down into two glucose molecules by hydrolysis. In living organisms, the enzyme maltase can achieve this very rapidly. In the laboratory, heating with a strong acid for several minutes will produce the same result.

Sucrose or cane sugar is the commonest of the disaccharides. It has the molecular formula C₁₂H₂₂O₁₁. It does not form a phenylhydrazone or exhibit carbonyl properties. On hydrolysis with dilute acids, it yields one molecule of D-(+)-glucose and one molecule of D-(—)-fructose. It is not a reducing sugar. 

Glucose and fructose are functional isomers of each other Because they have same molecular formula that is C₆H₁₂O₆ But different functional group in their chemical formula. Glucose has aldehyde group while fructose has ketone as functional group.

Lactose: The sugar found naturally in milk, it is a disaccharide composed of one galactose unit and one glucose unit; sometimes called milk sugar.

Because it is the chemical property of aliphatic aldehyde to give red precipitate with fehling solution.

RCHO + 2 CuO -----------> Cu₂O. + RCOOH

Fehling reagents is aq. alkaline CuSO₄ solution along with Rochelle salt Na-K tartrate.
And glucose molecule consists of aldehydic group at first position and hence it is also a aldehyde and thus give this characteristic test.

Fructose is an important ketohexose. It is obtained along with glucose by the hydrolysis of disaccharide, sucrose. The two monosaccharides are joined together by an oxide linkage formed by the loss of a water molecule. Such a linkage between two monosaccharide units through oxygen atom is called Glycosidic Linkage.

Glucose gives silver mirror test with Tollens reagent. It shows the presence of aldehyde group.
Also, mild oxidation of glucose with bromine water gives gluconic acid which shows the presence of aldehyde group.

Fehling's solution to make difference between carbohydrate and ketone functional grp and also used for differentiate reducing and non reducing sugar and as u know glucose is a reducing sugar so it will give red colour with fehling's solution (all monosachharides are reducing sugar).

• Disaccharides on hydrolysis with dilute acids or enzymes yield two molecules of either the same or different monosaccharides.
• The two monosaccharides are joined together by an oxide linkage formed by the loss of a water molecule. Such a linkage between two monosaccharide units through oxygen atom is called glycosidic linkage.

It forms glucose pentaacetate. The acetic anhydride esterifies with all the alcohol groups on the glucose ring.

Reaction of glucose with HI forms hexane. This reaction shows the presence of six carbons linked linearly in glucose.

The Molisch test uses concentrated sulphuric acid as the dehydrating acid. This acid dehydrates all carbohydrates, so the test is used to distinguish between carbohydrates and non-carbohydrates. 

The correct answer is Option A.
 
Glucose gets oxidized to cyanohydrin in reaction with HCN . This indicates that the carbonyl group is present as an aldehydic group.

Non-reducing sugars do not have an OH group attached to the anomeric carbon so they cannot reduce other compounds. All monosaccharides such as glucose are reducing sugars. A disaccharide can be a reducing sugar or a non-reducing sugar. Maltose and lactose are reducing sugars, while sucrose is a non-reducing sugar.

It is called invert sugar because the angle of the specific rotation of the plain polarized light changes from a positive to a negative value due to the presence of the optical isomers of the mixture of glucose and fructosesugars.

The pairs of optical isomers which differ in configuration around any other C atom other than C₁ atom are called epimers. D-glucose and D-mannose are C₂ epimers.

Hydrolysis of sucrose to give glucose and fructose is called inversion. hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+) to laevo (–) and the product is named as invert sugar.

Lactose intolerance is the inability to break down a type of natural sugar called lactose. Lactose is commonly found in dairy products, such as milk and yogurt. A person becomes lactose intolerant when his or her small intestine stops making enough of the enzyme lactase to digest and break down the lactose.

Sucrose is a non-reducing sugar because the two monosaccharide units are held together by a glycosidic linkage between C₁ of α-glucose and C₂ of β-fructose. Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucrose is a non-reducing sugar.