Explanation: The apoenzyme is the protein component. When combined with the required cofactor, it forms the complete holoenzyme.

Explanation: Cellulose forms long, unbranched chains that provide structural strength to plant cell walls.

Explanation: Lecithin is a phospholipid and an important component of biological membranes. Its hydrophilic and hydrophobic regions help it participate in membrane structure.

Explanation:

GLUT-4 transports glucose across cell membranes.

Insulin is a hormone that regulates blood glucose.

Trypsin is a protein-digesting enzyme.

Collagen is a structural protein found in connective tissue.

Explanation: The active site contains residues that help recognise the substrate and facilitate the reaction.

Explanation: Adenine and guanine are purines. Cytosine, thymine and uracil are pyrimidines.

Explanation: Lyases catalyse the removal or addition of groups without the usual mechanisms of hydrolysis or oxidation. Removal of a group can result in the formation of a double bond.

Explanation: In sucrose, the anomeric carbons of glucose and fructose are involved in the glycosidic bond. It therefore lacks a free anomeric carbon for the usual reducing-sugar reaction.

Explanation: Lipases hydrolyse ester bonds in lipids, nucleases cleave nucleic acids by breaking phosphodiester linkages, proteases hydrolyse peptide bonds, and amylases act on glycosidic bonds in starch.

Explanation: Carboxypeptidase is a zinc-containing metalloenzyme. Zinc ions help the enzyme catalyse the hydrolysis of peptide bonds. Flavin and haem participate in other biological processes, while niacin is a vitamin that contributes to coenzyme formation.

Explanation: Glycogen is a highly branched glucose polymer stored especially in liver and skeletal muscle.

Explanation: RNA contains ribose, whereas DNA contains deoxyribose.

Explanation: In competitive inhibition, the inhibitor competes with the substrate for the enzyme's active site. The apparent Km increases, but Vmax remains unchanged. The maximum reaction rate can still be reached by increasing the substrate concentration sufficiently.

Explanation: A peptide bond forms between the carboxyl group of one amino acid and the amino group of another.

Explanation: Enzymes accelerate reactions by providing a lower-activation-energy pathway. They do not alter the equilibrium constant or remove the need for energy coupling in energetically unfavourable reactions.

Explanation: Malonate resembles succinate structurally and competes for the enzyme's active site. It inhibits the conversion of succinate to fumarate. Increasing substrate concentration can reduce the effect of a reversible competitive inhibitor.

Explanation: A prosthetic group is a tightly bound non-protein component of an enzyme. Some enzymes require cofactors for catalytic activity, although not all enzymes need an additional cofactor. Therefore, the second statement is incorrect.

Repeated-question note: The cofactor/prosthetic-group concept was tested again in NEET-UG 2024 and NEET-UG 2025, with a related question on the haem prosthetic group in 2025. These are related concepts, not necessarily identical questions.

Explanation: When the substrate concentration is low, increasing the substrate concentration increases the reaction rate because more substrate molecules bind to the available enzymes.

When the substrate concentration becomes high, most enzyme active sites become occupied. The enzymes become saturated, and the reaction rate approaches its maximum value, called Vmax.

Explanation: Primary structure is the amino acid sequence. Secondary structure includes alpha helices and beta sheets. Disulphide bonds can stabilise tertiary structure, and haemoglobin is a familiar example of a protein with quaternary structure.

Explanation: Glutamic acid and aspartic acid are amino acids. Lecithin is a phospholipid, not a fatty acid. Arachidonic acid and palmitic acid are fatty acids.

Explanation: F₁ particles are associated with ATP synthase complexes on the inner mitochondrial membrane and project towards the matrix. Histones are associated with chromatin, axonemes form the internal structure of cilia and flagella, and plasmodesmata connect adjacent plant cells.

Explanation: The Golgi apparatus modifies, sorts and packages proteins and lipids. It also participates in the formation of glycoproteins and glycolipids. Aerobic respiration occurs mainly in mitochondria in eukaryotic cells, while translation occurs on ribosomes.

Explanation: The axoneme of a typical motile eukaryotic cilium or flagellum contains nine peripheral microtubule doublets and two central microtubules.

Explanation: The standard NCERT endomembrane system includes the endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles. Mitochondria, chloroplasts and peroxisomes are excluded because their functions are not coordinated with this system in the same way.

Explanation: The Golgi apparatus receives materials from the ER, modifies them, sorts them and dispatches them in vesicles to their destinations.

Explanation: Mitochondria and chloroplasts are double-membrane-bound organelles that contain their own DNA and ribosomes. They are considered semiautonomous because they can synthesize some proteins but depend on nuclear genes for many others. Neither is classified as part of the endomembrane system.

Explanation: The tonoplast is the membrane surrounding the vacuole. It regulates the movement of substances into and out of the vacuolar compartment.

Explanation: The nucleolus is a major site of rRNA synthesis. Centrioles have nine peripheral microtubule triplets in a characteristic arrangement. Leucoplasts store substances such as starch, oils and proteins. The Golgi apparatus participates in glycolipid formation and processing.

Explanation: Glyoxysomes are specialized microbodies that contain enzymes of the glyoxylate cycle. This pathway helps developing seedlings use stored lipids as a source of carbon for carbohydrate production.

Explanation: Smooth endoplasmic reticulum is involved in lipid synthesis and detoxification of drugs and other substances, particularly in liver cells. Rough ER is associated with the synthesis of many proteins.

Explanation: Lysosomal enzymes are synthesized on ribosomes associated with the rough ER and processed and sorted through the endomembrane system. The Golgi apparatus plays an important role in their sorting and delivery.

Explanation: Lysosomes are surrounded by a single membrane. The nucleus, mitochondria and chloroplasts have double-membrane boundaries.

Explanation: Ribosomes attached to the cytoplasmic surface of rough ER synthesize many proteins destined for secretion, insertion into membranes or delivery to the endomembrane system.

Explanation: Many secretory proteins enter the ER during synthesis, undergo processing and transport to the Golgi apparatus, and are then packaged into vesicles that deliver them to the plasma membrane for secretion.

Explanation: The Calvin cycle takes place in the chloroplast stroma. The light-dependent reactions take place in the thylakoid membranes.

Explanation: In eukaryotic cells, the enzymes of the Krebs cycle are located primarily in the mitochondrial matrix, with succinate dehydrogenase associated with the inner mitochondrial membrane.

Explanation: The cis face is generally the receiving side of the Golgi apparatus. The trans face is associated with sorting and dispatching processed materials.

Explanation: Ribosomes translate the information carried by mRNA into a polypeptide chain. They consist of rRNA and proteins and are not surrounded by a membrane.

Explanation: Smooth ER participates in lipid metabolism and steroid synthesis. It is prominent in many steroid-producing cells and also contributes to detoxification in certain tissues.

Explanation: Lysosomal acid hydrolases function optimally in an acidic environment. Raising the pH towards alkaline conditions reduces the activity of many of these enzymes and interferes with intracellular digestion.