Biomolecules – Chemical constituents of living cells: NEET MCQs with Answers

13 free questions on Biomolecules – Chemical constituents of living cells for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Chemical constituents of living cells: Biomolecules

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Question 1

Previous-year question
Match the compounds in List-I with their categories in List-II. [Re-NEET 2022]
List-I:
(a) Adenine
(b) Anthocyanin
(c) Chitin
(d) Codeine
List-II:
(i) Pigment
(ii) Polysaccharide
(iii) Alkaloid
(iv) Purine
  1. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
  2. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
  3. (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
  4. (a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)
Show answer
Answer: (A) (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
Explanation: Adenine is a purine (a-iv), anthocyanin is a pigment (b-i), chitin is a polysaccharide (c-ii) and codeine is an alkaloid (d-iii).

Question 2

Previous-year question
Which organic compound is correctly matched with its function? [NEET 2021 (Paper-2)]
  1. Uridine – A nucleotide that makes up RNA
  2. Phosphoglycerides – A component of cell membrane
  3. Serine – A non-protein amino acid
  4. GLUT-4 – Inhibits glucose transport into cells
Show answer
Answer: (B) Phosphoglycerides – A component of cell membrane
Explanation: Phosphoglycerides (phospholipids such as lecithin) are the main lipid components of the cell membrane. Uridine is a nucleoside (not a nucleotide), serine is a protein amino acid, and GLUT-4 enables (not inhibits) glucose transport into cells.

Question 3

Previous-year question
Match the following. (A) Inhibitor of catalytic activity; (B) Possess peptide bonds; (C) Cell wall material in fungi; (D) Secondary metabolite. (i) Ricin; (ii) Malonate; (iii) Chitin; (iv) Collagen. [NEET 2020]
  1. A-(iii), B-(i), C-(iv), D-(ii)
  2. A-(iii), B-(iv), C-(i), D-(ii)
  3. A-(ii), B-(iii), C-(i), D-(iv)
  4. A-(ii), B-(iv), C-(iii), D-(i)
Show answer
Answer: (D) A-(ii), B-(iv), C-(iii), D-(i)
Explanation: Malonate competitively inhibits succinic dehydrogenase, collagen is a protein with peptide bonds, chitin forms the fungal cell wall, and ricin is a toxic secondary metabolite of the castor plant.

Question 4

Previous-year question
Concanavalin A is [NEET 2019]
  1. an alkaloid
  2. an essential oil
  3. a lectin
  4. a pigment
Show answer
Answer: (C) a lectin
Explanation: Concanavalin A is a plant lectin, a carbohydrate-binding protein obtained from jack bean, and is a well known secondary metabolite.

Question 5

Previous-year question
In which one of the following is nitrogen NOT a constituent? [2004]
  1. Bacteriochlorophyll
  2. Pepsin
  3. Invertase
  4. Idioblast
Show answer
Answer: (D) Idioblast
Explanation: An idioblast is not a chemical compound at all but a specialised plant cell differing from those around it, such as a stone cell or an oil-containing cell, so the question of nitrogen does not arise. Bacteriochlorophyll contains a nitrogenous tetrapyrrole ring, and pepsin and invertase are proteins, whose amino acids all contain nitrogen.

Question 6

Previous-year question
Enzymes, vitamins and hormones can be grouped into a single category of biological chemicals because all of them [2005]
  1. are conjugated proteins
  2. help in regulating metabolism
  3. enhance oxidative metabolism
  4. are synthesised exclusively within the body of a living organism
Show answer
Answer: (B) help in regulating metabolism
Explanation: Enzymes, vitamins and hormones differ in chemical nature, but all three act as regulators of metabolic activity. They are not all proteins, they do not specifically enhance oxidative metabolism, and most vitamins cannot be synthesised in the body.

Question 7

Previous-year question
The most abundant organic compound on earth is [2000]
  1. lipid
  2. protein
  3. steroid
  4. cellulose
Show answer
Answer: (D) cellulose
Explanation: Cellulose is the principal structural material of plant cell walls, and since plants form the bulk of the earth's biomass it is the commonest organic compound on the planet. It is a straight-chain polymer of glucose that most animals cannot digest for want of cellulase.
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Question 8

Previous-year question
A living cell contains 60 to 75 per cent water. The water present in the human body is about [1991]
  1. 75–80%
  2. 60–65%
  3. 65–70%
  4. 50–55%
Show answer
Answer: (C) 65–70%
Explanation: Water constitutes roughly sixty-five to seventy per cent of the mass of the human body. It is the solvent in which all metabolic reactions take place, the medium of transport in blood and lymph, and, because of its high specific heat, an important stabiliser of body temperature.

Question 9

Previous-year question
The most abundant element present in plants is [2005]
  1. manganese
  2. carbon
  3. iron
  4. nitrogen
Show answer
Answer: (B) carbon
Explanation: Carbon forms the skeleton of every organic molecule and makes up the largest share of plant dry matter, most of it locked up in cellulose. It enters the plant as atmospheric carbon dioxide fixed during photosynthesis, whereas manganese and iron are needed only in trace amounts.

Question 10

Previous-year question
About 98 per cent of the mass of every living organism is made up of just six elements, including carbon, hydrogen, nitrogen, oxygen and [2010]
  1. calcium and phosphorus
  2. sulphur and magnesium
  3. phosphorus and sulphur
  4. magnesium and sodium
Show answer
Answer: (A) calcium and phosphorus
Explanation: Adding calcium and phosphorus to the four principal elements accounts for about ninety-eight per cent of the mass. Calcium dominates because of the skeleton, where it is deposited as calcium phosphate, and phosphorus is also essential to nucleic acids, phospholipids and ATP.

Question 11

Previous-year question
The four elements making up 99 per cent of a living system are [1993]
  1. carbon, hydrogen, oxygen and nitrogen
  2. carbon, hydrogen, oxygen and sulphur
  3. carbon, nitrogen, oxygen and phosphorus
  4. carbon, hydrogen, oxygen and phosphorus
Show answer
Answer: (A) carbon, hydrogen, oxygen and nitrogen
Explanation: Carbon, hydrogen, oxygen and nitrogen together account for about ninety-nine per cent of the atoms of any organism. Carbon's ability to form four stable covalent bonds and to link into chains and rings is the basis of the whole range of organic molecules, while nitrogen is indispensable to amino acids and nucleotides.

Question 12

Previous-year question
Which biomolecule is correctly characterised? [AIPMT Mains 2012]
  1. Palmitic acid — an unsaturated fatty acid with 18 carbons
  2. Adenylic acid — adenosine with a glucose phosphate
  3. Alanine — contains amino and acidic groups anywhere in the molecule
  4. Lecithin — a phosphorylated glyceride found in the cell membrane
Show answer
Answer: (D) Lecithin — a phosphorylated glyceride found in the cell membrane
Explanation: Lecithin is a phosphorylated glyceride found in the cell membrane.

Question 13

Previous-year question
The most abundant intracellular cation is [NEET-UG, 2013]
  1. K⁺
  2. Na⁺
  3. Ca²⁺
  4. H⁺
Show answer
Answer: (A) K⁺
Explanation: Potassium (K⁺) is the most abundant cation inside cells; Na⁺ dominates the extracellular fluid.

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