Nutrition Basics — Set 4

Correct Answer: B. Vitamin A

• **Vitamin A (Retinol)** = fat-soluble vitamin stored in hepatic stellate cells of the liver; can last months without dietary intake. • **Fat-soluble group** — vitamins A, D, E, and K dissolve in lipids and accumulate in body fat and liver, unlike B and C which flush out daily. • Excess Vitamin A can cause toxicity (hypervitaminosis A) precisely because it is stored, not excreted. • 💡 Option A (Vitamin B1) is wrong because thiamine is water-soluble and excreted in urine; Option C (Vitamin C) is wrong because ascorbic acid is water-soluble and not stored; Option D (Vitamin B6) is wrong because pyridoxine is water-soluble and requires daily replenishment.

Correct Answer: B. Proteins

• **Proteins** = enzymes are entirely or largely made of protein chains (polypeptides) folded into a precise 3-D active site. • **Catalytic mechanism** — the protein active site positions substrate molecules so that bonds break and form at rates billions of times faster than in the absence of the enzyme. • Some enzymes also need non-protein cofactors (vitamins/minerals), but the core catalytic scaffold is always protein. • 💡 Option A (Carbohydrates) is wrong because sugars serve as energy fuel and structural material, not as catalysts; Option C (Water) is wrong because water is a solvent enabling reactions, not a catalyst itself; Option D (Fats) is wrong because lipids function in energy storage and membrane structure, not catalysis.

Correct Answer: C. Vitamin C

• **Vitamin C (Ascorbic Acid)** = highly heat-labile and water-soluble; leaches into cooking water and oxidizes rapidly above 70°C. • **Oxidation sensitivity** — the enediol structure of ascorbic acid is easily broken by heat, light, and oxygen, destroying its antioxidant function. • Boiling vegetables can destroy up to 50–80% of their Vitamin C content, which is why raw or lightly steamed options are recommended. • 💡 Option A (Vitamin D) is wrong because calciferol is fat-soluble and relatively stable to moderate cooking heat; Option B (Vitamin A) is wrong because retinol is fat-soluble and survives normal cooking temperatures; Option D (Vitamin K) is wrong because phylloquinone is fat-soluble and more heat-resistant than water-soluble vitamins.

Correct Answer: B. Sodium

• **Sodium (Na⁺)** = the dominant extracellular cation; controls osmotic pressure, fluid volume, and water distribution between cells and plasma. • **Osmotic regulation** — kidneys adjust sodium excretion via aldosterone to keep serum osmolality near 285–295 mOsm/kg, directly governing total body water. • Low sodium (hyponatremia) causes cells to swell with water; high sodium (hypernatremia) causes dehydration of cells. • 💡 Option A (Iron) is wrong because iron is a component of hemoglobin for oxygen transport, not fluid balance; Option C (Copper) is wrong because copper acts as a cofactor in electron-transport enzymes like cytochrome c oxidase; Option D (Iodine) is wrong because iodine is incorporated into thyroid hormones T3 and T4, which regulate metabolism, not water balance.

Correct Answer: A. Bolus

• **Bolus** = the moist, rounded lump of chewed food mixed with salivary amylase and mucin, shaped by the tongue ready for swallowing. • **Salivary contribution** — saliva softens food, begins starch digestion via amylase, and lubricates the bolus for smooth passage through the esophagus. • Once swallowed, the bolus travels down the esophagus via peristalsis and enters the stomach where it becomes chyme. • 💡 Option B (Chyme) is wrong because chyme is the semi-liquid paste formed after gastric acid and pepsin act on the bolus inside the stomach; Option C (Succus) is wrong because succus entericus refers to intestinal juice secreted by the small intestine wall; Option D (Chyle) is wrong because chyle is the milky lymphatic fluid carrying absorbed dietary fats from the lacteals of the small intestine.

Correct Answer: C. Carbohydrates

• **Carbohydrates** = converted to blood glucose and stored as glycogen in muscle and liver; rapidly metabolized via glycolysis to produce ATP for intense exercise. • **Anaerobic glycolysis** — during sprinting or heavy lifting, oxygen supply is insufficient, so muscles rely entirely on carbohydrate breakdown since fat oxidation requires oxygen. • Elite athletes carbo-load before events specifically to maximize glycogen stores for sustained high-intensity output. • 💡 Option A (Proteins) is wrong because proteins are primarily used for muscle repair and enzyme synthesis, not immediate energy; Option B (Fats) is wrong because fat oxidation (beta-oxidation) is too slow to supply ATP at high exercise intensity; Option D (Vitamins) is wrong because vitamins act as enzyme cofactors enabling energy release but contain no caloric energy themselves.

Correct Answer: D. Vitamin B5

• **Vitamin B5 (Pantothenic Acid)** = essential for synthesizing Coenzyme A, which is required for fatty acid metabolism and myelin sheath maintenance in peripheral nerves. • **Burning feet** — pantothenic acid deficiency causes peripheral neuropathy: burning, tingling, and numbness in the soles of the feet, a condition documented in WWII prisoners of war. • Pantothenic acid is found in almost all foods (Greek: pantos = everywhere), so deficiency is rare but occurs with severe malnutrition. • 💡 Option A (Vitamin B6) is wrong because pyridoxine deficiency causes dermatitis and peripheral neuropathy but is specifically linked to glossitis and seborrheic dermatitis, not burning feet; Option B (Vitamin B9) is wrong because folic acid deficiency causes megaloblastic anemia and neural tube defects, not peripheral burning; Option C (Vitamin B12) is wrong because cobalamin deficiency causes subacute combined degeneration of the spinal cord, not burning feet specifically.

Correct Answer: C. Severe protein deficiency

• **Kwashiorkor** = severe protein deficiency with adequate or near-adequate calorie intake; the word comes from the Ga language of Ghana meaning 'disease of the displaced child'. • **Edema hallmark** — lack of plasma proteins (especially albumin) drops blood oncotic pressure, causing fluid to leak into the abdomen (ascites) and tissues, giving the classic swollen belly appearance. • Other signs include depigmented hair (flag sign), fatty liver, skin lesions, and growth retardation — all reflecting protein shortage. • 💡 Option A (Severe fat deficiency) is wrong because fat deficiency is extremely rare and presents with hormonal imbalance, not edema; Option B (Vitamin C deficiency) is wrong because ascorbic acid deficiency causes scurvy with bleeding gums and petechiae, not abdominal swelling; Option D (Calcium deficiency) is wrong because calcium deficiency leads to rickets or osteomalacia with weak, curved bones, not tissue edema.

Correct Answer: C. Vitamin B Complex

• **Vitamin B Complex** = all eight B vitamins function as coenzymes or coenzyme precursors — B1 (TPP), B2 (FAD/FMN), B3 (NAD/NADP), B5 (CoA), B6 (PLP), B7 (biotin), B9 (THF), B12 (methylcobalamin) — directly participating in energy metabolism. • **Central role in ATP production** — without B-vitamin coenzymes, the citric acid cycle, electron transport chain, and fatty acid beta-oxidation all stall. • B vitamins are water-soluble, which is why they must be replenished daily from food — they cannot be stored in bulk. • 💡 Option A (Vitamin D) is wrong because calciferol acts as a steroid hormone regulating calcium absorption in the intestine, not as a coenzyme in metabolic pathways; Option B (Vitamin A) is wrong because retinol functions in vision (rhodopsin synthesis) and gene expression regulation, not as a metabolic coenzyme; Option D (Vitamin E) is wrong because tocopherol is a lipid-soluble antioxidant protecting cell membranes from peroxidation, not a coenzyme.

Correct Answer: A. Calcium

• **Calcium** = dental enamel is 96% hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂], the calcium-phosphate crystal lattice that makes enamel the hardest substance the human body produces. • **Fluoride fortification** — fluoride substitutes for the OH group in hydroxyapatite to form fluorapatite, which is more acid-resistant and prevents cavity formation. • Enamel has no living cells once formed, so calcium-rich foods and fluoride during tooth development are critical for lifelong dental hardness. • 💡 Option B (Iron) is wrong because iron is the central atom of hemoglobin carrying oxygen in blood, not a structural mineral in teeth; Option C (Zinc) is wrong because zinc acts as a cofactor for metalloenzymes like carbonic anhydrase and DNA polymerase, not in enamel; Option D (Potassium) is wrong because potassium is the main intracellular cation for nerve action potentials and has no structural role in enamel.