Carbohydrates Questions in English

(A) glycosidic bond is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group,which may or may not be another carbohydrate.
Monosaccharides are the simplest form of carbohydrates and consist of a single sugar unit (e.g.,glucose,fructose).
Since they consist of only one unit,they do not contain any glycosidic bonds.
Disaccharides,oligosaccharides,and polysaccharides are formed by the linkage of two or more monosaccharide units through glycosidic bonds.
Therefore,the correct answer is $A$.

(C) In a healthy individual,the concentration of glucose in the blood is maintained within a narrow range.
According to the $NCERT$ textbook for Class $11$ Biology (Chapter $9$: Biomolecules),the concentration of glucose in the blood of a healthy person is $4.5-5.0 \text{ mM}$.
This concentration is crucial for maintaining metabolic homeostasis in the body.

(B) Sucrose is a disaccharide formed by the condensation of one molecule of glucose and one molecule of fructose.
It is a non-reducing sugar and is the primary form in which carbohydrates are translocated through the phloem in plants.

(A) Starch is a polysaccharide composed of amylose and amylopectin. When starch reacts with iodine $(I_2)$, the iodine molecules get trapped within the helical structure of the amylose component. This complex formation results in a characteristic deep blue or blue-black color. Therefore, the reaction is: $\text{Starch} + I_2 \rightarrow \text{Blue-black complex}$.

(B) The formation of disaccharides from monosaccharides is as follows:
$1$. Glucose + Glucose $\rightarrow$ Maltose $(P)$
$2$. Glucose + Galactose $\rightarrow$ Lactose $(Q)$
$3$. Glucose + Fructose $\rightarrow$ Sucrose $(R)$
Therefore,the correct sequence is $P = \text{Maltose}$,$Q = \text{Lactose}$,and $R = \text{Sucrose}$.

(D) Option $D$ is the correct answer.
Cellulose is a linear polysaccharide consisting of a long chain of glucose units linked by $\beta-1, 4$-glycosidic bonds.
Unlike starch,which contains amylose (a helical structure that traps iodine molecules to produce a blue color),cellulose does not form complex helical structures.
Because it lacks these complex helices,it cannot hold iodine molecules,and therefore,it does not produce a blue color with iodine.

(C) Glycogen is a highly branched polysaccharide of glucose.
$1$. It has only one reducing end (at the start of the chain) and many non-reducing ends (at the end of each branch).
$2$. The structure contains $\alpha 1-4$ glycosidic bonds in the linear chains and $\alpha 1-6$ glycosidic bonds at the branching points.
$3$. In glycogen,the number of $\alpha 1-4$ glycosidic bonds is significantly higher than the number of $\alpha 1-6$ glycosidic bonds because branching occurs only every $8-12$ glucose units.
$4$. Therefore,the statement that '$\alpha 1-6$ glycosidic bond is more than $\alpha 1-4$ glycosidic bond' is incorrect.

(A) Cellulose is a linear,fibrous polysaccharide found in the cell walls of plants.
It is a homopolymer,meaning it is composed of only one type of monomeric unit.
The monomeric unit of cellulose is $D$-glucose,which are linked together by $\beta-1, 4$-glycosidic bonds.
Therefore,the correct answer is Glucose.

(A) The iodine test ($I_2$ test) is used to detect the presence of starch. Starch consists of amylose and amylopectin. Amylose is a helical molecule that can hold $I_2$ molecules in its helical structure,producing a blue-black color.
Cellulose is a linear polymer of $\beta$-$D$-glucose units linked by $\beta(1 \rightarrow 4)$ glycosidic bonds. Due to its linear structure,it does not form complex helices like starch.
Because it lacks these helices,cellulose cannot trap $I_2$ molecules and therefore does not give a positive iodine test.
Thus,both the Assertion and the Reason are true,and the Reason correctly explains why cellulose does not give the $I_2$ test.

(B) Lactose is a disaccharide composed of two monosaccharide units: glucose and galactose.
The enzyme lactase catalyzes the hydrolysis of lactose into its constituent monosaccharides.
The reaction is represented as: $\text{Lactose} + \text{H}_2\text{O} \xrightarrow{\text{Lactase}} \text{Glucose} + \text{Galactose}$.
Therefore,the correct products are glucose and galactose.

(C) Statement $I$ is correct because lactose is a disaccharide composed of glucose and galactose,which yields these two monosaccharides upon hydrolysis.
Statement $II$ is incorrect because,although galactose can be converted into glucose-$6$-phosphate to enter the glycolytic pathway,it does not play the exact same role as glucose directly in respiration. Glucose is the primary respiratory substrate that enters glycolysis directly,whereas galactose requires additional enzymatic conversion steps before it can be utilized in cellular respiration.

(D) Two monosaccharides are linked together by a covalent bond known as a glycosidic bond.
This bond is formed by a dehydration synthesis reaction,where a water molecule is removed between the hydroxyl groups of the two monosaccharides.
This linkage is characteristic of disaccharides and polysaccharides.

(A) In animals,the primary storage form of carbohydrates is $Glycogen$.
$Glycogen$ is a highly branched polymer of glucose,which is stored mainly in the liver and muscles to be used as an energy reserve.
$Starch$ is the storage form of carbohydrates in plants,while $Cellulose$ is a structural polysaccharide found in plant cell walls.
Therefore,the correct option is $A$.

(C) Carbohydrates are classified based on their hydrolysis products.
$Starch$ and $Glycogen$ are polysaccharides, which yield many monosaccharide units upon hydrolysis.
$Sucrose$ is a disaccharide, which upon hydrolysis yields two monosaccharide units (glucose and fructose).
$Fructose$ is a monosaccharide, which is the simplest form of carbohydrate and cannot be further hydrolysed into smaller sugar molecules.

(B) The correct matches are as follows:
$I$. Glucose is the primary respiratory substrate and acts as the fuel of the living cell $(I-c)$.
$II$. Fructose is commonly known as fruit sugar $(II-d)$.
$III$. Cellulose is a structural polysaccharide and a major component of the plant cell wall $(III-b)$.
$IV$. Starch is the primary storage polysaccharide (reserve food) in plants $(IV-a)$.
Therefore,the correct matching is $I-c, II-d, III-b, IV-a$.

(D) Cane sugar is the common name for sucrose.
Sucrose is a disaccharide composed of one molecule of glucose and one molecule of fructose linked by a glycosidic bond.
It is extracted primarily from sugarcane and sugar beets.
Therefore,the correct option is $D$.

(B) Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones.
This means they contain multiple hydroxyl $(OH)$ groups along with either an aldehyde $(CHO)$ or a ketone ($C$=$O$) functional group.
Carboxyl $(COOH)$ groups are characteristic of organic acids,such as fatty acids,and are not a defining feature of carbohydrate molecules.

(D) Disaccharides are carbohydrates formed when two monosaccharides are joined together by a glycosidic bond.
This process involves the removal of a water molecule $(H_2O)$,which is known as a condensation reaction or dehydration synthesis.
For example,the formation of sucrose from glucose and fructose involves the elimination of one water molecule.

(D) Mono- and disaccharides are crystalline,sweet in taste,and soluble in water.
In contrast,polysaccharides such as starch,glycogen,and cellulose are complex carbohydrates that are not sweet.
They are characterized by being amorphous (lacking a defined crystalline structure) and are generally insoluble in water.

(C) The general empirical formula for most carbohydrates is $(CH_2O)_n$.
Galactose $(C_6H_{12}O_6)$ follows this formula where $n=6$.
Maltose $(C_{12}H_{22}O_{11})$ is a disaccharide formed by two glucose units minus a water molecule,and it closely approximates the ratio.
Glycogen is a polysaccharide of glucose,also following the $(CH_2O)_n$ ratio.
Digitoxose is a deoxy sugar with the chemical formula $C_6H_{12}O_4$. Because it lacks an oxygen atom compared to standard hexoses,it does not fit the $(CH_2O)_n$ empirical formula.

(A) . Cellulose.
Cellulose is a fibrous homopolysaccharide that forms the structural element of the cell wall in all plants,some fungi,and protists.
It is the primary component of cotton fibre,which is nearly pure cellulose.

(C) The correct answer is $C$.
In a polysaccharide,individual monosaccharide units are linked together by a glycosidic bond.
This bond is formed through a dehydration synthesis reaction between the hydroxyl group of one monosaccharide and the carbon atom of an adjacent monosaccharide.

(D) The correct answer is $D$.
Lactose is a disaccharide sugar composed of two monosaccharide units: $D$-glucose and $D$-galactose.
It is naturally found in milk and dairy products,acting as a primary source of energy for infants and young mammals.