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.