Question 1

Muscle cells store energy in the form of;?

Accepted Answer

Answer reason: Skeletal muscle stores glucose as glycogen, which can be rapidly mobilized during activity to supply ATP via glycolysis. Humans do not synthesize starch; it is a plant storage polysaccharide. Cellulose is a structural plant polysaccharide that humans cannot produce or digest. Therefore, only glycogen is correct.

Question 2

Urea produce by ...?

Accepted Answer

Answer reason: Urea is synthesized in the liver via the urea (ornithine) cycle, which detoxifies ammonia produced from amino acid catabolism. The kidneys and their nephrons excrete urea but do not produce it. The pancreas is involved in digestive enzymes and hormone secretion, not nitrogen waste production.

Question 3

Most cell membranes are composed principally of?

Accepted Answer

Answer reason: Biological membranes are primarily a phospholipid bilayer with embedded proteins. Lipids provide the hydrophobic barrier and fluid matrix, while proteins serve transport, receptor, and enzymatic functions. DNA and RNA are not membrane structural components, and chitin is a polysaccharide found in fungal cell walls, not membranes.

Question 4

Ketoacidosis occurs due to the deficient intake of-?

Accepted Answer

Answer reason: When carbohydrate intake is insufficient, insulin levels fall and lipolysis increases, producing excess ketone bodies (acetoacetate, beta-hydroxybutyrate) from fat. Accumulation of these organic acids leads to metabolic acidosis—ketoacidosis—as seen in starvation or poorly controlled diabetes. Deficiencies of fat, protein, or minerals do not cause ketone overproduction and acidosis.

Question 5

Glycogen is stored in?

Accepted Answer

Answer reason: The liver is the principal storage site for glycogen in humans, used to maintain blood glucose during fasting via glycogenolysis. While skeletal muscle also stores glycogen, it is not among the options. Brain and skin have negligible glycogen stores, and the heart contains only small amounts not used for systemic glucose regulation. Therefore, liver is the best answer.

Question 6

Optimum pH of pepsin is?

Accepted Answer

Answer reason: Pepsin is a gastric protease that functions in the highly acidic environment of the stomach. It is activated from pepsinogen by gastric HCl and has an optimum pH around 1.5–2. At neutral or alkaline pH, pepsin becomes inactive or denatures. Therefore, 2.0 is the best answer.

Question 7

Enzymes are composed of?

Accepted Answer

Answer reason: Most enzymes are globular proteins composed of amino acids that fold into specific three‑dimensional structures to catalyze reactions by lowering activation energy. While rare catalytic RNAs (ribozymes) exist, the predominant biological catalysts in cells are proteins. Lipids and carbohydrates are structural or energy-storage molecules, and DNA serves as genetic material, not the typical composition of enzymes.

Question 8

Urea cycle complete by?

Accepted Answer

Answer reason: The urea cycle, which detoxifies ammonia by converting it to urea, occurs almost exclusively in hepatocytes. Initial steps occur in the mitochondrial matrix and the remaining steps in the cytosol of liver cells. Kidneys primarily excrete urea but do not possess the full enzyme set for its synthesis. Therefore, the cycle is completed in the liver.

Question 9

Which of the following is the major function of carbohydrates ...?

Accepted Answer

Answer reason: Carbohydrates primarily serve as energy reserves (e.g., glycogen in animals and starch in plants) and also provide structural components such as cellulose in plant cell walls and chitin in arthropods. While they participate in cell recognition and signaling, material transport is not a principal function of carbohydrates. Therefore, both storage and structural framework represent major functions.

Question 10

The human body does not produce?

Accepted Answer

Answer reason: Humans synthesize DNA through replication, produce hormones via endocrine glands, and make enzymes as cellular proteins. In contrast, most vitamins cannot be synthesized endogenously in sufficient amounts and must be obtained from the diet. While there are limited exceptions (e.g., vitamin D synthesis in skin), the general principle is that vitamins are essential micronutrients not produced by the body. Therefore, vitamins are the item the human body does not produce.

Question 11

Which protein is found in egg whites?

Accepted Answer

Answer reason: Egg white (albumen) consists mostly of water and proteins, with ovalbumin being the predominant protein component. Collagen is a structural protein of connective tissue, not egg white. Keratin is found in hair, skin, and nails. Oxytocin is a peptide hormone and is not a component of egg whites.

Question 12

Enzymes are chemically?

Accepted Answer

Answer reason: Most enzymes are globular proteins that act as biological catalysts by lowering activation energy and increasing reaction rates. Their activity depends on amino acid sequence and three-dimensional structure forming active sites. Although some RNA molecules (ribozymes) have catalytic activity, the vast majority of enzymes in cells are proteins.

Question 13

Enzyme activity is measured in terms of?

Accepted Answer

Answer reason: Enzyme activity is defined by the velocity of the reaction it catalyzes, typically measured as the rate of product formation per unit time under specified conditions. pH influences activity but is not the metric of activity itself. Km describes substrate affinity, and inhibition constants describe inhibitor potency; neither directly quantifies activity. Therefore, the appropriate measure is the reaction rate.

Question 14

Cofactor is?

Accepted Answer

Answer reason: Cofactors are non-protein chemical components required for some enzymes to become catalytically active. They may be metal ions (e.g., Mg2+, Zn2+) or organic molecules called coenzymes. They are distinct from the substrate or product and are not structural regions like the active site; instead, they assist in catalysis or stabilize enzyme structure.

Question 15

Ribosomes are sites for?

Accepted Answer

Answer reason: Ribosomes translate mRNA into polypeptide chains, making them the cellular site of protein synthesis. Photosynthesis occurs in chloroplasts, not ribosomes. Fat (lipid) synthesis is primarily associated with the smooth endoplasmic reticulum and cytosolic enzymes. Aerobic respiration occurs mainly in mitochondria.

Question 16

The first enzyme isolated in pure crystalline form was?

Accepted Answer

Answer reason: Urease was the first enzyme crystallized in pure form, achieved by James B. Sumner in 1926 from jack beans. This work provided decisive evidence that enzymes are proteins, earning Sumner the Nobel Prize in Chemistry in 1946. Pepsin, amylase, and catalase were characterized later but were not the first to be crystallized.

Question 17

Which organ in the human body stores glycogen?

Accepted Answer

Answer reason: The liver is the primary organ that stores glycogen and breaks it down via glycogenolysis to maintain blood glucose between meals under regulation by insulin and glucagon. Skeletal muscle also stores glycogen, but it is used locally for muscle energy and is not released into the bloodstream. The kidney, heart, and brain do not serve as major systemic glycogen reservoirs.

Question 18

Enzyme action is affected by?

Accepted Answer

Answer reason: Enzyme activity depends on environmental conditions and substrate availability. Temperature and pH alter enzyme conformation and active-site chemistry; deviations from the optimum can reduce activity or denature the protein. Substrate concentration increases reaction rate until active sites become saturated, reaching Vmax. Therefore, all listed factors affect enzyme action.

Question 19

Which vitamin acts as a coenzyme?

Accepted Answer

Answer reason: Many B vitamins function directly as coenzymes or are precursors to coenzymes essential for metabolic reactions. Examples include thiamine pyrophosphate (B1), FAD/FMN from riboflavin (B2), NAD/NADP from niacin (B3), coenzyme A from pantothenic acid (B5), and pyridoxal phosphate from B6. In contrast, vitamins A and D act as hormones and regulators, and vitamin C serves mainly as a reducing agent and antioxidant rather than a classic coenzyme.

Question 20

Vmax of an enzyme is?

Accepted Answer

Answer reason: Vmax is the maximum rate of an enzyme-catalyzed reaction when the enzyme's active sites are saturated with substrate. Beyond this point, increasing substrate concentration does not increase rate. Vmax depends on enzyme concentration and catalytic efficiency but is distinct from Km, which reflects substrate affinity. Certain inhibitors (e.g., noncompetitive) can reduce the apparent Vmax.

Question 21

Which of the following is a ribozyme?

Accepted Answer

Answer reason: Ribozymes are RNA molecules with catalytic activity. The peptidyl transferase center of the ribosome is rRNA, which catalyzes peptide bond formation—demonstrating ribozyme activity. Pepsin and most ribonucleases are protein enzymes, and tRNA functions in amino acid delivery without catalytic activity. Therefore, ribosomal RNA is the ribozyme.

Question 22

Enzymes work by?

Accepted Answer

Answer reason: Enzymes catalyze reactions by lowering the activation energy, often by stabilizing the transition state and properly orienting substrates. This increases the reaction rate without being consumed in the process. Raising activation energy would slow a reaction, not speed it. Increasing substrate concentration or temperature can affect rate but are not the mechanism by which enzymes inherently work.

Question 23

Competitive inhibition occurs when?

Accepted Answer

Answer reason: In competitive inhibition, a molecule resembling the substrate binds reversibly to the enzyme's active site, competing with the substrate. This increases the apparent Km (more substrate needed to reach half-maximal velocity) while Vmax remains unchanged because high substrate can outcompete the inhibitor. Denaturation is not a form of competitive inhibition, and low substrate or product feedback do not define this mechanism.

Question 24

Which of the following is not a characteristic of enzymes?

Accepted Answer

Answer reason: Enzymes act as biological catalysts that speed reactions without being consumed. They are highly specific for their substrates and are sensitive to temperature, with excess heat causing denaturation. Because enzymes emerge unchanged from reactions and can be reused, the statement 'used up in reactions' is not a characteristic.

Question 25

Hemoglobin is a ?

Accepted Answer

Answer reason: Hemoglobin is a conjugated protein made of four globin polypeptide chains, each linked to a heme group. The iron in heme binds oxygen reversibly, allowing red blood cells to transport oxygen. Fats, vitamins, and carbohydrates are not polypeptide macromolecules and do not perform this oxygen-carrying function.

Question 26

Metabolism is referred to as?

Accepted Answer

Answer reason: Metabolism encompasses both anabolism (the synthesis of complex biomolecules from simpler ones) and catabolism (the breakdown of complex molecules), which together maintain cellular energy balance. Catabolic pathways release energy, often captured as ATP, whereas anabolic pathways consume energy to build macromolecules. Therefore, metabolism refers to both synthesis and breakdown of biomolecules.

Question 27

Enzyme is chemically a?

Accepted Answer

Answer reason: Most enzymes are proteins composed of amino acids whose specific tertiary and quaternary structures create active sites for catalysis. Their activity often depends on cofactors or coenzymes but the catalytic component is the protein. While a few catalytic RNAs (ribozymes) exist, the general biochemical classification of enzymes is protein.

Question 28

The term “lock and key model” is associated with?

Accepted Answer

Answer reason: The lock-and-key model explains enzyme specificity, where the active site's shape is complementary to its substrate, allowing precise binding. It describes catalysis with minimal conformational change compared with the induced-fit model. DNA replication and protein synthesis are unrelated nucleic acid processes. Although antigen–antibody binding shows specificity, the classic lock-and-key model is defined for enzyme–substrate interactions.

Question 29

Which of the following elements is not found in living organism?

Accepted Answer

Answer reason: Magnesium, iron, and sodium are essential elements in living systems: Mg2+ is a key enzymatic cofactor and part of chlorophyll, Fe is required for hemoglobin and electron transport, and Na+ is the major extracellular cation in animals. Silicon is not an essential bioelement for most animals and humans and is generally not incorporated into their biochemistry. While some organisms (e.g., diatoms, sponges) use silicon, it is not a typical or required element across living organisms compared with the others listed.

Question 30

The energy currency of the cell is called ________?

Accepted Answer

Answer reason: ATP is the primary energy currency of the cell; hydrolysis of its terminal phosphate bond releases energy to drive cellular processes. DNA and RNA serve genetic information storage and expression, not immediate energy transfer. ADP is a lower-energy product formed when ATP is hydrolyzed and is converted back to ATP during cellular respiration.

Question 31

The by products of all foods oxidized in the body are;?

Accepted Answer

Answer reason: Complete cellular oxidation of all macronutrients converts carbon to carbon dioxide and hydrogen to water while capturing released energy as ATP and heat. Oxygen is a reactant, not a byproduct, and intermediates such as glucose, fatty acids, glycerol, or amino acids are substrates rather than universal end products. Therefore, the common byproducts of food oxidation are carbon dioxide, water, and energy.

Question 32

The general formula of carbohydrate?

Accepted Answer

Answer reason: Carbohydrates are classically described as hydrates of carbon, with a general empirical formula (CH2O)n or Cn(H2O)n, reflecting a 2:1 hydrogen-to-oxygen ratio. Glucose (C6H12O6) is an example that fits this pattern but is a specific molecule rather than the general formula. Options B and D do not maintain the characteristic 2:1 H:O ratio found in carbohydrates.

Question 33

Brain gets energy from ketone bodies if availability of glucose is?

Accepted Answer

Answer reason: The brain primarily uses glucose, but during prolonged fasting or carbohydrate restriction it adapts to use ketone bodies (acetoacetate and β-hydroxybutyrate) produced by the liver. This occurs when glucose availability is low, reducing the need for gluconeogenesis and sparing protein. It does not switch to ketones when glucose is high or constant, and a true zero glucose level is incompatible with life.

Question 34

How many phases of glycolysis?

Accepted Answer

Answer reason: Glycolysis is classically divided into two phases: the energy investment phase and the energy payoff phase. In the investment phase, ATP is consumed to phosphorylate glucose and prepare it for cleavage. In the payoff phase, ATP is generated via substrate-level phosphorylation and NADH is produced, yielding a net of 2 ATP per glucose. Therefore, there are two phases.

Question 35

Glycogen is present in all body except?

Accepted Answer

Answer reason: Glycogen is an intracellular storage form of glucose found primarily in the liver and in muscles, including cardiac muscle. Many tissues contain small amounts of glycogen for local energy reserves. It does not circulate in the bloodstream; only glucose and other metabolites are present in blood. Therefore, blood is the exception.

Question 36

Which of these is not a lipid?

Accepted Answer

Answer reason: Proteins are polymers of amino acids linked by peptide bonds and constitute a distinct macromolecule class from lipids. Lipids are hydrophobic molecules that include fats (triacylglycerols), oils, and waxes. Therefore, among the options, proteins are the only one that is not a lipid.

Question 37

ATP is an example of?

Accepted Answer

Answer reason: ATP (adenosine triphosphate) is the cell’s primary energy currency. Hydrolysis of its terminal phosphate releases energy that drives many cellular processes such as muscle contraction and active transport. Chemically it is a nucleotide, not an enzyme, protein, or vitamin.

Question 38

The chemical formula for water is?

Accepted Answer

Answer reason: Water consists of two hydrogen atoms covalently bonded to one oxygen atom, giving the molecular formula H2O. H3O represents the hydronium ion, not neutral water. HO denotes a hydroxyl radical, and H3O2 is not the formula for water (hydrogen peroxide is H2O2). Therefore, H2O is the only correct choice.

Question 39

What type of bond connects monomers in carbohydrates and lipids?

Accepted Answer

Answer reason: Monomers of carbohydrates (monosaccharides) are linked through glycosidic bonds, and fatty acids are linked to glycerol in lipids via ester bonds; both are covalent bonds. Peptide bonds specifically join amino acids in proteins. Ionic and hydrogen bonds are non-covalent interactions important for structure and stability but do not form the primary links between monomers in these macromolecules.

Question 40

DNA is an example of?

Accepted Answer

Answer reason: DNA is a polymer of nucleotides composed of a deoxyribose sugar, phosphate group, and nitrogenous bases. It stores and transmits genetic information, the defining function of nucleic acids. Proteins are amino acid polymers, carbohydrates are sugars and polysaccharides, and lipids are hydrophobic molecules, none of which describe DNA’s structure or function.

Question 41

The main excretory product of protein metabolism is?

Accepted Answer

Answer reason: Amino acid deamination produces ammonia, which is detoxified in the liver via the urea cycle to form urea, the primary nitrogenous waste in humans. Urea is then excreted by the kidneys. Creatinine is a byproduct of creatine phosphate metabolism, and uric acid results from purine breakdown; neither is the main product of protein catabolism. Glucose is not an excretory waste product.

Question 42

Correct example of an amphoteric oxide is?

Accepted Answer

Answer reason: Amphoteric oxides can react with both acids and bases. Aluminum oxide (Al2O3) shows amphoteric behavior: it reacts with acids to form aluminum salts and with strong bases to form aluminates. In contrast, Na2O and MgO are predominantly basic oxides and mainly react with acids, not bases, so they are not amphoteric. Therefore, Al2O3 is the single best answer.

Question 43

Cotton fibres are made of ________?

Accepted Answer

Answer reason: Cotton is a plant-derived fiber, and plant cell walls are primarily composed of cellulose, a polysaccharide made of β(1→4) linked glucose units. Cotton fibers are essentially almost pure cellulose, which gives them strength and absorbency. Fats and proteins are not the main structural polymers of cotton fibers, and starch is a storage carbohydrate rather than the primary cell-wall fiber component.

Question 44

The main classes of molecules in biochemistry (often called biomolecules) are?

Accepted Answer

Answer reason: The major biomolecule classes studied in biochemistry include carbohydrates, lipids, proteins, and nucleic acids. Each class represents a fundamental category of biological macromolecules with distinct structures and functions in cells. Since all four listed categories are correct, the best answer is the option indicating all are included.

Question 45

All of the following are coenzyme except?

Accepted Answer

Answer reason: NAD, FAD, and NADP are classic redox coenzymes derived from B vitamins that act as electron carriers in metabolic reactions. ADP (adenosine diphosphate) is primarily an energy-transfer nucleotide involved in phosphorylation/ATP synthesis rather than functioning as an enzyme-associated coenzyme. Therefore, ADP is the exception among the listed choices.

Question 46

What is Cholesterol ...?

Accepted Answer

Answer reason: Cholesterol is a sterol (a steroid alcohol) with the characteristic four-ring steroid nucleus. It is a key structural component of cell membranes and serves as the precursor for steroid hormones, bile acids, and vitamin D. While it is transported with lipids and often grouped with fats in diet discussions, chemically it is classified as a steroid.

Question 47

Excessive bleeding during an injury is a deficiency of?

Accepted Answer

Answer reason: Vitamin K is required for hepatic gamma-carboxylation of clotting factors II, VII, IX, and X (and proteins C and S), enabling normal coagulation. Deficiency impairs clot formation and commonly presents as easy bruising, mucosal bleeding, and prolonged bleeding after minor injury. In contrast, vitamin A deficiency mainly affects vision/epithelial integrity, vitamin B deficiencies vary by specific B vitamin, and vitamin E deficiency is more associated with neurologic/hemolytic issues rather than primary bleeding diathesis.

Question 48

During Respiration, Energy is produced in..?

Accepted Answer

Answer reason: Cellular respiration captures energy released from glucose oxidation and stores it primarily as ATP via substrate-level phosphorylation and oxidative phosphorylation. ATP is the immediate usable energy currency for cellular work. ADP is the lower-energy precursor that is phosphorylated to form ATP, while CO2 is a waste product and NADP is mainly associated with photosynthesis/anabolic redox rather than ATP production in respiration.

Question 49

Which of the following are components of a phospholipid?

Accepted Answer

Answer reason: A phospholipid is built on a glycerol backbone with two fatty acid tails and a phosphate-containing head group (often with an additional polar substituent). This amphipathic structure explains how phospholipids form cell membranes with hydrophobic tails inward and hydrophilic heads outward. Cholesterol is a separate lipid that can insert into membranes but is not a core component of phospholipids, and amino acids/monosaccharides are not standard phospholipid building blocks.

Question 50

Monooxygenases are found in?

Accepted Answer

Answer reason: The classic monooxygenase system refers to the cytochrome P450–dependent mixed-function oxidase enzymes located in the smooth endoplasmic reticulum. In subcellular fractionation, the smooth ER forms microsomes, so these enzymes are described as being found in microsomes. While some P450 enzymes also exist in mitochondria, the standard answer for monooxygenases in drug metabolism questions is microsomes (SER).

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