MPSC 2025 Prelims Paper-I · Question 69 of 100

Correct — option (4), A – iii, B – iv, C – i, D – ii. Each pairing here follows directly from how many simple sugar (monosaccharide) units are joined together to form the carbohydrate: A, Monosaccharide, pairs with iii, Glucose, because glucose is itself a single six-carbon simple sugar (an aldohexose) and cannot be broken down into smaller sugar units — it is the basic building block from which the other three carbohydrates in this list are constructed. B, Disaccharide, pairs with iv, Sucrose, because ordinary table sugar is formed from exactly two monosaccharide units — one glucose and one fructose — joined by a glycosidic bond. C, Trisaccharide, pairs with i, Raffinose, because raffinose is a three-unit sugar composed of galactose, glucose and fructose linked together, commonly found in beans, cabbage and whole grains. D, Polysaccharide, pairs with ii, Starch, because starch is a large polymer made of many hundreds to thousands of glucose units linked together (as the branched chains amylose and amylopectin), making it the plant's principal energy-storage carbohydrate. This progression — one glucose unit, two units, three units, many units — is exactly the mono-/di-/tri-/polysaccharide classification the question is testing, and option (4) is the only arrangement that assigns each carbohydrate to its correct unit-count category.

• (1)A – iii, B – ii, C – i, D – iv — This correctly pairs A with iii (glucose is indeed the monosaccharide) but then swaps the disaccharide and polysaccharide assignments: it pairs B, Disaccharide, with ii, Starch — but starch is a large polymer of many glucose units, not a two-unit sugar — and it pairs D, Polysaccharide, with iv, Sucrose — but sucrose is only a two-unit disaccharide, far too small to be classed as a polysaccharide. The trisaccharide pairing (C with i, raffinose) is correct here, but the disaccharide/polysaccharide swap makes the set as a whole wrong.
• (2)A – ii, B – i, C – iii, D – iv — This option scrambles nearly every pairing: it assigns A, Monosaccharide, to ii, Starch, even though starch is a large polysaccharide, not a single simple sugar; it assigns B, Disaccharide, to i, Raffinose, even though raffinose is a three-unit trisaccharide, not a two-unit sugar; it assigns C, Trisaccharide, to iii, Glucose, even though glucose is the single-unit monosaccharide; and it leaves D, Polysaccharide, paired with iv, Sucrose, a two-unit disaccharide far too small to be a polysaccharide. Every one of the four pairings inverts the actual unit-count relationship.
• (3)A – iv, B – iii, C – ii, D – i — This option also inverts every pairing: A, Monosaccharide, is matched to iv, Sucrose, a two-unit disaccharide rather than a single simple sugar; B, Disaccharide, is matched to iii, Glucose, which is itself only a monosaccharide with no second unit to make it a disaccharide; C, Trisaccharide, is matched to ii, Starch, a many-thousand-unit polysaccharide rather than a three-unit sugar; and D, Polysaccharide, is matched to i, Raffinose, which is only a three-unit trisaccharide, far short of the many-unit chain a polysaccharide requires. Each pairing sits one or more categories away from where the actual unit count places it.

Carbohydrates are classified by how many monosaccharide (simple sugar) units are linked together by glycosidic bonds. A monosaccharide, such as glucose, fructose or galactose, is a single sugar unit that cannot be hydrolysed into a simpler sugar. A disaccharide forms when two monosaccharide units join — sucrose (glucose + fructose), lactose (glucose + galactose) and maltose (glucose + glucose) are the classic examples. A trisaccharide forms when three monosaccharide units join, as in raffinose (galactose + glucose + fructose), a sugar found in beans, cabbage, broccoli and whole grains, notable for being partly indigestible by humans and contributing to gas production when these foods are eaten. A polysaccharide is a large polymer built from many monosaccharide units — often hundreds or thousands — joined in long chains; starch (a plant glucose-storage polymer made of amylose and amylopectin), glycogen (the animal equivalent) and cellulose (the structural plant polysaccharide) are the standard examples.

MPSC's biochemistry questions frequently test this monosaccharide-disaccharide-trisaccharide-polysaccharide ladder using match-the-columns questions because the classification is unambiguous and rewards precise recall over intuition: a candidate must know not just that sucrose and starch are both 'carbohydrates' but exactly how many sugar units compose each one. Raffinose, as the trisaccharide example, is a useful discriminator because it is less commonly taught than sucrose or starch, so a candidate who has only memorised the two most familiar examples (a disaccharide and a polysaccharide) is likely to misplace it.

• Glucose is a monosaccharide — a single simple sugar unit that cannot be broken into smaller sugars.
• Sucrose is a disaccharide, formed from one glucose unit and one fructose unit joined by a glycosidic bond.
• Raffinose is a trisaccharide, formed from galactose, glucose and fructose units, found in beans, cabbage and whole grains.
• Starch is a polysaccharide, a large polymer of many glucose units arranged as amylose and amylopectin, serving as the plant's energy store.
• Carbohydrate classification (mono-/di-/tri-/polysaccharide) is based strictly on the number of monosaccharide units joined together.

• Assuming any 'large-sounding' sugar name (like raffinose) must be a polysaccharide, rather than checking its actual unit count
• Confusing a disaccharide (two units) with a monosaccharide (one unit) when the sugar sounds equally simple or familiar
• Assigning starch, a large polymer, to the disaccharide category by mistaking 'plant sugar' familiarity for a specific unit count
• Forgetting that a monosaccharide like glucose is itself the building block from which di-, tri- and polysaccharides are all constructed

MPSC biochemistry questions commonly use match-the-columns format to test carbohydrate classification, pairing familiar and unfamiliar sugar names against the mono-/di-/tri-/polysaccharide categories, rewarding candidates who know each sugar's actual unit composition rather than a general sense of which sugars are 'simple' or 'complex'.

No directly related past PYQ was found.

• practice — not a real PYQ

  Raffinose, found in beans and cabbage, is classified as which type of saccharide ?

  • (a)Monosaccharide
  • (b)Disaccharide
  • (c)Trisaccharide
  • (d)Polysaccharide

  Answer(c) Trisaccharide — raffinose is composed of three monosaccharide units, galactose, glucose and fructose, joined by glycosidic bonds.

• practice — not a real PYQ

  Sucrose, common table sugar, is formed by the joining of which two monosaccharide units ?

  • (a)Glucose and Galactose
  • (b)Glucose and Fructose
  • (c)Fructose and Galactose
  • (d)Glucose and Glucose

  Answer(b) Glucose and Fructose — sucrose is a disaccharide formed when one glucose unit and one fructose unit join by a glycosidic bond.