Tag: carbohydrates - definition and classification

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Multiple choice carbohydrates - definition and classification introduction to carbohydrates biomolecules chemistry

Carbohydrates are ___________.

  1. used to make a paper

  2. produced as an intermediate in the synthesis of proteins

  3. the polyhydroxy aldehyde or polyhydroxy ketone

  4. all of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketone. Cellulose is a carbohydrate used to make a paper. Carbohydrates are also produced as an intermediate in the synthesis of protein.

Multiple choice carbohydrates - definition and classification introduction to carbohydrates biomolecules chemistry

The polyhydroxy aldehydes are called:

  1. proteins

  2. fats

  3. carbohydrates

  4. vitamins
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • Polyhydroxy aldehydes or ketones are molecules with more than one hydroxyl group $(−OH)$, and a carbonyl group $(C=O)$ either at the terminal carbon atom (aldose) or at the second carbon atom (ketose) are called carbohydrates.
  • Monosaccharides are polyhydroxy aldehydes and are called Simple Sugar, any of the basic compounds that serve as the building blocks of carbohydrates. 
Multiple choice carbohydrates - definition and classification introduction to carbohydrates biomolecules chemistry

D-glucose & D-fructose can be differentiated by :

  1. Fehling solution

  2. Tollens reagent

  3. Benedict test
  4. $Br _2/H _2O$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$Br _2/H _2O$ being a mild oxidising agent can only oxidise aldose to carboxylic acids but cannot oxidise ketose.


As glucose contains aldehyde group it gets oxidised and converted into a carboxylic acid and is differentiate from fructose which has ketone group.

Therefore, the correct option is D.

Multiple choice carbohydrates - definition and classification introduction to carbohydrates biomolecules chemistry

Free aldehyde group can be produced on hydrolysis of which of the following compound(s)?

  1. Maltose

  2. Sucrose
  3. $\alpha$-D Glucose

  4. Lactose
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

 $\alpha$-D glucose has cyclic hemiacetal structure. Hemiacetal on hydrolysis gives free aldehyde group.
Maltose, sucrose and lactose are are disacharides which on hydrolysis gives monosaccharides in which aldehyde group becomes free.
Maltose  $\displaystyle \xrightarrow { \text { hydrolysis} }$ Glucose $\displaystyle + $ glucose.
Sucrose  $\displaystyle \xrightarrow { \text { hydrolysis} }$ Glucose $\displaystyle + $ fructose.
Lactose  $\displaystyle \xrightarrow { \text { hydrolysis} }$ Glucose $\displaystyle + $ galactose.

Multiple choice carbohydrates - definition and classification introduction to carbohydrates biomolecules chemistry

Which of the following is a physical property of sugar?

  1. It is a white crystalline solid.

  2. Carbon, hydrogen, and oxygen are its constituents.
  3. It turns black when concentrated $\displaystyle { H } _{ 2 }{ SO } _{ 4 } $ reacts with it.

  4. When heated it decomposes.

  5. It decomposes readily.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Colour and appearance are physical properties.
The remaining are chemical properties which include its composition, reaction with sulphuric acid and decomposition.