Chemical Constituents of Cells Practice Questions
20 free Chemical Constituents of Cells practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is an example of a secondary metabolite that is used as a drug?
- A Carotenoids
- B Vinblastine
- C Abrin (toxin)
- D Ricin (toxin)
Correct answer: Vinblastine
Vinblastine is a plant-derived secondary metabolite from Catharanthus roseus used as an anticancer drug that inhibits cell division. Abrin and ricin are plant toxins, while carotenoids are accessory pigments.
When performing a chemical analysis of living tissue using trichloroacetic acid, the 'acid-insoluble pool' represents which of the following?
- A Micromolecules
- B Biomacromolecules
- C Cytoplasmic composition
- D Amino acids and sugars
Correct answer: Biomacromolecules
The acid-insoluble fraction (retentate) contains biomacromolecules like proteins, nucleic acids, and polysaccharides. These molecules have molecular weights exceeding 800 Daltons.
Which of the following is the most abundant protein in the whole of the biosphere?
- A Collagen
- B Hemoglobin
- C RuBisCO enzyme
- D Insulin hormone
Correct answer: RuBisCO enzyme
Ribulose bisphosphate carboxylase-oxygenase (RuBisCO) is the most abundant protein in the biosphere due to its central role in photosynthetic carbon fixation in plants and algae. Collagen is the most abundant protein in the animal world.
Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon. This carbon is known as the:
- A Beta-carbon
- B Gamma-carbon
- C Alpha-carbon
- D Delta-carbon
Correct answer: Alpha-carbon
Amino acids are substituted methanes where the amino group and carboxylic group are attached to the alpha-carbon. Hence, they are referred to as alpha-amino acids.
Which amino acid contains sulfur in its structure?
- A Serine
- B Cysteine
- C Tyrosine
- D Proline
Correct answer: Cysteine
Cysteine and methionine are the two standard amino acids that contain sulfur. Serine contains a hydroxyl group, while tyrosine is aromatic.
Lipids are generally water insoluble. A fatty acid with no double bonds between carbon atoms is described as:
- A Unsaturated
- B Saturated
- C Polyunsaturated
- D Trans-unsaturated
Correct answer: Saturated
Saturated fatty acids have no double bonds between carbon atoms in their hydrocarbon chain, which allows tight packing and solid consistency at room temperature. Unsaturated fatty acids contain one or more double bonds in the chain.
Lecithin is an example of a:
- A Simple lipid
- B Nitrogenous base
- C Phospholipid
- D Triglyceride
Correct answer: Phospholipid
Lecithin is a phosphorus-containing lipid found in cell membranes. It is classified as a phospholipid and is vital for membrane structure.
Which of the following nitrogenous bases is found exclusively in RNA and not in DNA?
- A Adenine
- B Guanine
- C Uracil (RNA only)
- D Thymine
Correct answer: Uracil (RNA only)
Uracil is found exclusively in RNA, replacing thymine found in DNA. Unlike thymine, uracil lacks a methyl group at position 5. Adenine, guanine, and cytosine are present in both DNA and RNA.
A nucleoside is formed when a nitrogenous base is linked to a sugar. What is the resulting structure when a phosphate group is also attached to the nucleoside?
- A Nucleotide
- B Nucleic acid
- C Dinucleotide
- D Polynucleotide
Correct answer: Nucleotide
A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group. A nucleoside lacks the phosphate group. Linking many nucleotides produces a polynucleotide chain, and nucleic acids are formed from such chains.
Proteins are heteropolymers of amino acids. Which type of bond links individual amino acids together?
- A Glycosidic bond
- B Peptide bond
- C Phosphodiester bond
- D Hydrogen bond
Correct answer: Peptide bond
The peptide bond is formed between the carboxyl group of one amino acid and the amino group of the next, with the elimination of water. This bond is essential for forming polypeptide chains.
The 'Primary Structure' of a protein refers to:
- A The 3D folding of the chain
- B The sequence of amino acids
- C The presence of alpha-helices
- D The assembly of multiple subunits
Correct answer: The sequence of amino acids
The primary structure is the linear sequence of amino acids in a polypeptide. It dictates the identity of the first, second, and subsequent amino acids in the chain.
In a polysaccharide chain, the individual monosaccharides are linked by which bond?
- A Peptide bond
- B Ester bond linkage
- C Glycosidic bond
- D Disulfide covalent bond
Correct answer: Glycosidic bond
Glycosidic bonds are covalent bonds formed by dehydration between the anomeric carbon of one monosaccharide and a hydroxyl group of another. This bond links sugars to form polysaccharide chains like starch or cellulose.
Which of the following is a polymer of fructose?
- A Starch (glucose)
- B Cellulose
- C Glycogen
- D Inulin (fructose)
Correct answer: Inulin (fructose)
Inulin is a storage polysaccharide found in plants like Dahlia tubers and is a polymer of fructose units. Starch and glycogen are polymers of glucose; cellulose is a structural glucose polymer found in plant cell walls.
The chitinous exoskeleton of arthropods is formed by the polymerization of:
- A Glucose monomers
- B N-acetyl glucosamine
- C Amino acid chains
- D Fatty acid lipids
Correct answer: N-acetyl glucosamine
Chitin is a complex polysaccharide that forms the structural exoskeleton of arthropods. It is a homopolymer of N-acetyl glucosamine units linked by beta-1,4-glycosidic bonds.
In the B-DNA model proposed by Watson and Crick, the pitch of the helix is:
- A 3.4 nm
- B 0.34 nm
- C 2.0 nm
- D 34 nm
Correct answer: 3.4 nm
The pitch of the B-DNA helix is 3.4 nm per turn, with 10 base pairs per turn. This results in a distance of 0.34 nm between consecutive base pairs.
Which protein structure is absolutely necessary for the biological activity of enzymes?
- A Primary structure
- B Secondary structure
- C Tertiary structure
- D Quaternary structure
Correct answer: Tertiary structure
The tertiary structure involves the folding of the polypeptide into a 3D shape, creating 'pockets' or active sites. This conformation is vital for enzyme-substrate interactions.
Essential oils like sandalwood or lemon grass oil are classified as:
- A Primary metabolites
- B Secondary metabolites
- C Structural lipids only
- D Nitrogen-based alkaloids
Correct answer: Secondary metabolites
Secondary metabolites are compounds produced by plants or fungi not directly involved in normal growth or reproduction. Essential oils like sandalwood and lemongrass are categorized as secondary metabolites, alongside pigments and toxins.
Which of the following is NOT a characteristic of zwitterionic form of amino acids?
- A It carries both positive and negative charges.
- B It occurs at a specific pH called the isoelectric point.
- C The amino group is protonated and the carboxyl group is deprotonated.
- D The molecule moves toward the cathode in an electric field.
Correct answer: The molecule moves toward the cathode in an electric field.
In its zwitterionic form, the net charge of the amino acid is zero. Therefore, it does not migrate toward either the anode or cathode in an electric field.
The most abundant element in the human body by weight percentage is:
- A Carbon element
- B Hydrogen
- C Oxygen element
- D Nitrogen
Correct answer: Oxygen element
Oxygen constitutes approximately 65% of the human body's mass. This is largely because water (which is about 89% oxygen by weight) makes up the majority of the body. Carbon follows at about 18.5%.
What is the function of the protein GLUT-4?
- A Acts as an intercellular ground substance
- B Enables glucose transport into cells
- C Fights infectious agents
- D Acts as a sensory receptor
Correct answer: Enables glucose transport into cells
GLUT-4 is a specialized protein that facilitates the transport of glucose across cell membranes. It is insulin-responsive and critical for maintaining blood sugar levels.