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Biology 12th MCQ PDF - All Chapters
NCERT Based MCQ with Explanation:
1. What is the most abundant chemical in living organisms?
(A) Proteins
(B) Lipids
(C) Nucleic Acids
(D) Water
Explanation: Water constitutes 70-90% of the total cellular mass in living organisms. This high percentage makes it the most abundant chemical in living organisms, essential for maintaining cellular structure and facilitating biochemical reactions.
2. What are biomolecules?
(A) Only inorganic molecules
(B) Molecules synthesized only by plants
(C) Carbon compounds from living tissues
(D) Gases like oxygen and nitrogen
Explanation: Biomolecules are carbon compounds found in living organisms, including amino acids, sugars, fatty acids, nucleotides, and more. They are critical for various biological functions.
3. What is the role of secondary metabolites in living organisms?
(A) Directly involved in growth
(B) Play known roles in physiological processes
(C) Used for energy storage
(D) Often useful for human welfare (e.g., drugs, pigments)
Explanation: Secondary metabolites are compounds like alkaloids, flavonoids, and pigments that are not essential for basic physiological processes but are valuable for ecological interactions or commercial use (e.g., medicines, pigments).
4. Which of the following is a polysaccharide?
(A) Glucose
(B) Sucrose
(C) Starch
(D) Glycerol
Explanation: Starch is a polysaccharide composed of long chains of glucose molecules. It is used as a storage form of energy in plants, unlike glucose or sucrose, which are simple sugars.
5. Which compound contains nitrogen in its molecular structure?
(A) Carbohydrates
(B) Amino acids
(C) Lipids
(D) Glycerol
Explanation: Amino acids contain both an amino group (–NH2) and a carboxyl group (–COOH). The nitrogen in the amino group is a critical component for building proteins.
6. What are nucleotides composed of?
(A) Amino acids, phosphate, and sugar
(B) Phosphate, nitrogenous base, and sugar
(C) Lipids, proteins, and sugar
(D) Fatty acids, glycerol, and phosphate
Explanation: Nucleotides, the building blocks of nucleic acids, consist of three components: a phosphate group, a nitrogenous base (adenine, thymine, cytosine, guanine), and a pentose sugar (ribose or deoxyribose).
7. Which protein is the most abundant in the biosphere?
(A) Collagen
(B) Actin
(C) Rubisco
(D) Myosin
Explanation: Rubisco (Ribulose bisphosphate carboxylase-oxygenase) is the most abundant protein on Earth, playing a central role in the process of carbon fixation during photosynthesis.
8. What type of biomolecule is glycogen?
(A) Protein
(B) Lipid
(C) Polysaccharide
(D) Nucleic acid
Explanation: Glycogen is a polysaccharide made of glucose monomers. It serves as the primary storage form of glucose in animals and is found mainly in the liver and muscles.
9. What is the main function of enzymes in biological reactions?
(A) To act as structural components
(B) To catalyze chemical reactions
(C) To store genetic information
(D) To transport nutrients
Explanation: Enzymes are biological catalysts that speed up the rate of chemical reactions in cells by lowering the activation energy required for the reaction to occur.
10. Which of the following is a protein with a quaternary structure?
(A) Myoglobin
(B) Hemoglobin
(C) Insulin
(D) Glucose
Explanation: Hemoglobin has a quaternary structure consisting of four polypeptide subunits, two α-chains, and two β-chains. This structure allows hemoglobin to effectively bind and transport oxygen.
Science MCQ, Class 10th, Chapter-9, Light: Reflection and Refraction11. What is the significance of the R group in amino acids?
(A) It determines the type of amino acid
(B) It stores energy
(C) It binds to enzymes
(D) It forms polysaccharides
Explanation: The R group (side chain) in amino acids is variable and determines the specific properties and classification (e.g., polar, nonpolar) of each amino acid.
12. Which enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid?
(A) Lipase
(B) Amylase
(C) Carbonic anhydrase
(D) Trypsin
Explanation: Carbonic anhydrase catalyzes the rapid conversion of carbon dioxide and water into carbonic acid, which is critical for maintaining pH balance in blood and other tissues.
13. What is the primary structure of a protein?
(A) The arrangement of amino acids in a chain
(B) The three-dimensional folding of the protein
(C) The interaction between multiple polypeptides
(D) The α-helix and β-pleated sheets
Explanation: The primary structure of a protein refers to the linear sequence of amino acids in a polypeptide chain, which determines the protein's final structure and function.
14. Which type of enzyme inhibitor resembles the substrate and competes for the active site?
(A) Allosteric inhibitor
(B) Competitive inhibitor
(C) Non-competitive inhibitor
(D) Uncompetitive inhibitor
Explanation: A competitive inhibitor resembles the substrate and binds to the active site of the enzyme, preventing the substrate from binding and thus inhibiting the enzyme's activity.
15. What is the primary role of lipids in the cell membrane?
(A) To provide energy storage
(B) To form the structural framework
(C) To catalyze reactions
(D) To bind nucleotides
Explanation: Lipids, particularly phospholipids, form the structural basis of cell membranes. Their hydrophobic and hydrophilic regions create a bilayer that separates the cell from its external environment.
16. Which of the following is a macromolecule?
(A) Glucose
(B) Fatty acid
(C) DNA
(D) ATP
Explanation: DNA is a nucleic acid and a macromolecule made of long chains of nucleotides. It carries genetic information critical for the functioning and reproduction of living organisms.
17. What is the quaternary structure of a protein?
(A) The sequence of amino acids
(B) The interaction between multiple polypeptide chains
(C) The folding of a polypeptide into a 3D shape
(D) The formation of disulfide bridges
Explanation: The quaternary structure refers to the way in which different polypeptide chains (subunits) interact and assemble into a functional protein complex, such as in hemoglobin.
18. Which of the following is a disaccharide?
(A) Glucose
(B) Maltose
(C) Fructose
(D) Galactose
Explanation: Maltose is a disaccharide composed of two glucose molecules. It is formed during the digestion of starch and is a sugar used by the body for energy.
19. Which of the following molecules is a purine?
(A) Thymine
(B) Cytosine
(C) Adenine
(D) Uracil
Explanation: Adenine and guanine are purines, which have a double-ring structure. Thymine, cytosine, and uracil are pyrimidines, which have a single-ring structure.
20. In proteins, what type of bond links amino acids together?
(A) Hydrogen bond
(B) Ionic bond
(C) Peptide bond
(D) Phosphodiester bond
Explanation: Amino acids in a protein are linked by peptide bonds, which are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another.
21. Which polysaccharide serves as an energy storage form in animals?
(A) Starch
(B) Glycogen
(C) Cellulose
(D) Chitin
22. Which nitrogenous base is found only in RNA and not in DNA?
(A) Adenine
(B) Thymine
(C) Uracil
(D) Guanine
23. What kind of bond holds together the two strands of a DNA molecule?
(A) Peptide bond
(B) Hydrogen bond
(C) Phosphodiester bond
(D) Ionic bond
24. What is the structural role of cellulose in plants?
(A) Energy storage
(B) Genetic material
(C) Structural support
(D) Hormone production
25. What is the main function of ribozymes?
(A) Storing genetic information
(B) Acting as enzymes
(C) Serving as structural components
(D) Facilitating DNA replication
26. What kind of reaction is catalyzed by hydrolases?
(A) Oxidation-reduction
(B) Hydrolysis
(C) Transfer of functional groups
(D) Isomerization
27. Which of the following biomolecules is a micromolecule?
(A) DNA
(B) RNA
(C) Glucose
(D) Protein
28. What type of enzyme regulation involves the binding of a molecule at a site other than the active site?
(A) Competitive inhibition
(B) Non-competitive inhibition
(C) Feedback inhibition
(D) Substrate inhibition
29. Which of the following is an example of a nucleotide?
(A) ATP
(B) Glucose
(C) Amino acid
(D) Glycerol
30. What is the main function of phospholipids in the cell membrane?
(A) To act as enzymes
(B) To store energy
(C) To form the bilayer structure
(D) To regulate gene expression