Question

 Which of the following are not secondary metabolites in plants? [NEET 2021]

(a) Morphine, codeine

(b) Amino acids, glucose

(c) Vinblastine, curcumin

(d) Rubber, gums

Answer/Explanation

Ans. (b)
Primary metabolites are compounds that are directly involved in the growth and development of a plant like amino acids and sugars (glucose). Primary metabolites prominently function growth, development and reproduction of cell. Secondary metabolites are compounds produced in other metabolic pathways that, although important, are not essential for the functioning of the plant. 

Question

Floridean starch has structure similar to [NEET (Sep.) 2020]

(a) amylopectin and glycogen

(b) mannitol and algin

(c) laminarin and cellulose

(d) starch and cellulose

Answer/Explanation

Ans. (a)

Floridean starch has structure similar to amylopectin and glycogen as both are made from $\alpha$-D glucose monomers. The key difference between amylopectin and glycogen is, amylopectin is a soluble form of starch, while glycogen is an insoluble form of starch.

Question

 Which two functional groups are characteristic of sugars? [NEET 2018]

(a) Carbonyl and phosphate

(b) Carbonyl and methyl

(c) Hydroxyl and methyl

(d) Carbonyl and hydroxyl

Answer/Explanation

Ans. (d)
Sugars are chemically carbohydrates.
They are polyhydroxy aldoses, ketoses and their condensation products.
Aldoses bear a terminal aldehyde or – $\mathrm{CHO}$ group while ketoses have an internal ketone or -CO group.
Thus, they possess two functional groups, i.e. carbonyl and hydroxyl.

Question

The chitinous exoskeleton of arthropods is formed by the polymerisation of [CBSE AIPMT 2015]

(a) keratin sulphate and chondroitin sulphate

(b) D-glucosamine

(c) N-acetyl glucosamine

(d) lipoglycans

Answer/Explanation

Ans. (b)

The chitinous exoskeleton of arthropods is formed by the polymerisation of $\mathrm{N}$-acetyl glucosamine, which is a derivative of glucose. It is also a characteristic component of the cell wall of fungi, the radulae of molluscs and the beaks and internal shells of cephalopods, including squid and octopuses.

Question

 Which one of the following is a non-reducing carbohydrate? [CBSE AIPMT 2014]

(a) Maltose

(b) Sucrose

(c) Lactose

(d) Ribose 5-phosphate

Answer/Explanation

Ans. (b)
Sucrose is a disaccharide of glucose and fructose. It is a non-reducing sugar as it do not contain any free anomeric carbon atom. Maltose is a disaccharide of 2 glucose units. Its first glucose residue cannot undergo oxidation, whereas, second residue can undergo oxidation because it has a reactive free anomeric carbon atom. Hence, it is a reducing sugar.
Lactose and ribose-5-phosphate are also reducing in nature due to the presence of a free ketonic or aldehyde group.

Question

 Macromolecule chitin is [NEET 2013]

(a) nitrogen containing polysaccharide

(b) phosphorus containing polysaccharide

(c) sulphur containing polysaccharide

(d) simple polysaccharide

Answer/Explanation

Ans. (a)

Macromolecule chitin is a complex polysaccharide containing amino sugars and chemically modified sugars, (e.g. glucosamine, $\mathrm{N}$-acetyl galactosamine, etc). Polysaccharides are long carbohydrate molecules of monosaccharide units joined together by glycosidic bonds. They have a general formula $\mathrm{C}_x\left(\mathrm{H}_2 \mathrm{O}\right)_y$. Chitin is the main component of the cell wall of fungi, the exoskeletons of arthropods, insects and radulae of molluscs, etc.

Question

 Which one of the following pairs is wrongly matched? [CBSE AIPMT 2009]

(a) Detergents – Lipase

(b) Alcohol $\quad-$ Nitrogenase

(c) Fruit juice – Pectinase

(d) Textile $\quad-$ Amylase

Answer/Explanation

Ans. (b)

The wrongly matched pair is ‘b’ because alcohol (ethyl alcohol) can be produced by fermentation of any carbohydrate, containing a fermentable sugar.

The development of synthetic alcohol follows following reaction

Question

About 98 per cent of the mass of every living organism is composed of just six elements including carbon, hydrogen, nitrogen, oxygen and [CBSE AIPMT 2007]

(a) phosphorus and sulphur

(b) sulphur and magnesium

(c) magnesium and sodium

(d) calcium and phosphorus

Answer/Explanation

Ans. (a)

About $98 \%$ of the mass of every living organism including bacterium and human beings is composed of just six elements, i.e. Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P) and Sulphur (S). Charagaff(1950) suggested that despite wide compositional variations exhibited by different types of DNA the total amount of purines equaled the total amount of pyrimidines $(A+G=T+C)$.

Question

Which of the following is a reducing sugar? [CBSE AIPMT 2002]

(a) Galactose

(b) Gluconic acid

(c) $\beta$-methyl galactoside

(d) Sucrose

Answer/Explanation

Ans. (a)

Glucose, fructose, mannose, galactose are hexose monosaccharides. The monosaccharides have free aldehyde or ketone group which can reduce $\mathrm{Cu}^{2+}$ to Cu. Therefore, these are called reducing sugars.

Question

 Most abundant organic compound on earth is [CBSE AIPMT 2001, 04]

(a) protein

(b) cellulose

(c) lipids

(d) steroids

Answer/Explanation

Ans. (b)

Cellulose is fibrous polysaccharide that forms the structural component of plant cell wall, some primitive fungi and tunic of ascidians. Cellulose is the most abundant organic substance on earth. It can be digested by only a few microbes present in the gut of ruminants and white ants.

Question

Lactose is composed of [CBSE AIPMT 1998]

(a) glucose+glucose

(b) glucose+fructose

(c) fructose+galactose

(d) glucose+galactose

Answer/Explanation

Ans. (d)

Lactose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ is a disaccharide found in mammalian milk. It comprises of galactose and glucose units which are linked together by $\beta, 1-4$ glycosidic bonds. It is a reducing sugar.

Question

 Cellulose, the most important constituent of plant cell wall is made of [CBSE AIPMT 1998]

(a) unbranched chain of glucose molecules linked by $\alpha$ 1, 4-glycosidic bond

(b) branched chain of glucose molecules linked by $\boldsymbol{\beta}$ 1, 4-glycosidic bond in straight chain and $\alpha, 1,6$-glycosidic bond at the site of branching

(c) unbranched chain of glucose molecules linked by $\boldsymbol{\beta}$ 1, 4-glycosidic bond

(d) branched chain of glucose molecules linked by $\alpha$ 1, 6-glycosidic bond at the site of branching

Answer/Explanation

Ans. (c)

Cellulose $\left(\mathrm{C}_6 \mathrm{H}_{10} \mathrm{O}_5\right)_n$ is the most abundant organic polymer. It is a polysaccharide and consists of long unbranched chains of glucose residues linked by $\beta, 1-4$ glycosidic bonds. In plants, cellulose is formed from sugar. It serves as building material in the formation of cell wall.

Question

 In which one of the following groups, all the three are examples of polysaccharides? [CBSE AIPMT 1996]

(a) Starch, glycogen, cellulose

(b) Sucrose, maltose, glucose

(c) Glucose, fructose, lactose

(d) Galactose, starch, sucrose

Answer/Explanation

Ans. (a)

Starch and glycogen are storage polysaccharide and cellulose is a structural polysaccharide. Starch has straight chain of 1,4 $\alpha-\mathrm{D}$ pyranose glucose units and side chains or amylopectin part of 2-200 thousand glucose units that are attached to straight chains by $1,6 \alpha$-D glycosidic bonds.
Glycogen is long chain branched polymer of 5-300 thousand glucose units, straight chain linked by $\alpha-D$ 1-4 glycosidic bonds and side chains through $\alpha-D 1 \rightarrow 6$ glycosidic bonds.
Cellulose, a fibrous polysaccharide has a linear chain of 6-10 thousand $1 \rightarrow 4$ linked $\beta$-pyranose glucose chain.

Question

Glycogen is a polymer of [CBSE AIPMT 1992]

(a) galactose

(b) glucose

(c) fructose

(d) sucrose

Answer/Explanation

Ans. (b)

A glycogen molecule is a long highly branched chain of about 30000 to $100000 \alpha-D$ glucose units joined by glycosidic bonds. It is storage form of glucose, popularly called animal starch. It provides energy to animals, fungi and bacteria.

Question

 Living cell contains 60-75\% water. Water present in human body is [CBSE AIPMT 1992]

(a) $60-65 \%$

(b) $50-55 \%$

(c) $75-80 \%$

(d) 65-70\%

Answer/Explanation

Ans. (d)

In humans, about two-third of body is formed of water. About $65-70 \%$ of human body is water, of these about $55 \%(20-22 \mathrm{~L})$ is confined to cells as intracellular water.

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