Nutrition Basics — Set 2

Correct Answer: B. Fish Oil

• **Fish Oil** = the richest dietary source of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), the two long-chain omega-3 fatty acids most active in the human body. • **Cardiovascular benefits** — omega-3s from fish oil lower serum triglycerides, reduce platelet aggregation, and decrease inflammatory cytokines, cutting heart-disease risk. • DHA is also the primary structural fat in the brain and retina, making fish oil important for neurological development in infants. • 💡 Option A (Butter) is wrong because it is rich in saturated fatty acids that raise LDL cholesterol, the opposite cardiovascular effect; Option C (Potatoes) is wrong because they are starchy carbohydrates with negligible fat content; Option D (Rice) is wrong because it is a grain providing mainly carbohydrates with no significant omega-3 content.

Correct Answer: B. Transporting oxygen

• **Hemoglobin** = an iron-containing protein in red blood cells that binds oxygen in the lungs and releases it in peripheral tissues for aerobic cellular respiration. • **Heme iron** — each hemoglobin molecule carries four heme groups, each with one Fe²⁺ ion that reversibly binds one O₂ molecule, allowing a single RBC to carry ~1 billion oxygen molecules. • Iron deficiency reduces hemoglobin production, causing anemia with fatigue and shortness of breath. • 💡 Option A (Digesting fats) is wrong because fat digestion is carried out by bile salts and pancreatic lipase in the small intestine; Option C (Regulating sugar) is wrong because blood glucose is controlled by insulin and glucagon from the pancreas; Option D (Building bones) is wrong because bone formation requires calcium, phosphate, and osteoblast cells.

Correct Answer: A. Vitamin D

• **Vitamin D (Calciferol)** = UV-B radiation (290–315 nm) converts 7-dehydrocholesterol in the skin to pre-vitamin D3, which is then thermally isomerized to cholecalciferol (D3). • **Activation pathway** — D3 is hydroxylated first in the liver to 25-OH-D and then in the kidney to the active 1,25(OH)₂D (calcitriol), which promotes calcium absorption. • People with dark skin, limited sun exposure, or living at high latitudes are at greatest risk of deficiency. • 💡 Option B (Vitamin C) is wrong because ascorbic acid cannot be synthesized in the skin and must be obtained entirely from dietary sources; Option C (Vitamin B) is wrong because the B vitamins come from food and gut bacteria, not photosynthesis in skin; Option D (Vitamin A) is wrong because retinol is obtained from animal foods or converted in the liver from dietary beta-carotene.

Correct Answer: D. Proteins

• **Proteins** = long chains of amino acids that fold into specific three-dimensional shapes, functioning as enzymes that catalyze every biochemical reaction and as peptide hormones (e.g., insulin, glucagon) that regulate metabolism. • **Amino acid building blocks** — 20 amino acids combine in countless sequences; 9 are essential and must come from diet because the body cannot synthesize them. • Proteins are also structural (collagen, keratin), transport (hemoglobin), immune (antibodies), and contractile (actin, myosin) molecules. • 💡 Option A (Fats) is wrong because although some hormones are steroid-based (made from cholesterol), enzymes are always proteins; Option B (Carbohydrates) is wrong because they provide fuel and structural polysaccharides but are not the backbone of hormones or enzymes; Option C (Water) is wrong because it is the solvent for biochemical reactions, not a structural building block.

Correct Answer: D. Ascorbic acid

• **Ascorbic acid (Vitamin C)** = a six-carbon lactone that acts as a powerful reducing agent and antioxidant, donating electrons to neutralize reactive oxygen species. • **Collagen synthesis** — ascorbic acid is a required cofactor for prolyl hydroxylase, the enzyme that cross-links collagen chains; deficiency causes scurvy with bleeding gums and poor wound healing. • Humans, unlike most animals, cannot synthesize ascorbic acid and must obtain it entirely from diet. • 💡 Option A (Acetic acid) is wrong because it is CH₃COOH — the compound that gives vinegar its sour taste, not a vitamin; Option B (Citric acid) is wrong because it is the tart acid found in citrus fruit flesh used as a preservative, not the same as vitamin C; Option C (Folic acid) is wrong because it is vitamin B9, required for DNA nucleotide synthesis and prevention of neural tube defects.

Correct Answer: C. Potassium

• **Potassium (K⁺)** = the principal intracellular cation; the Na⁺/K⁺-ATPase pump moves 3 Na⁺ out and 2 K⁺ into the cell per ATP cycle, maintaining the resting membrane potential crucial for nerve impulses and muscle contraction. • **Hypokalemia** — low blood potassium disrupts the pump, causing muscle weakness, cardiac arrhythmias, and paralysis in severe cases. • Potassium-rich foods include bananas, oranges, potatoes, and leafy greens. • 💡 Option A (Magnesium) is wrong because magnesium activates ATP (as Mg-ATP) needed by the pump but is not itself the ion transported; Option B (Iron) is wrong because iron is a component of hemoglobin and electron transport chains, not of the sodium-potassium pump; Option D (Zinc) is wrong because zinc stabilizes protein structures (zinc fingers) and is involved in immune function, not Na⁺/K⁺ transport.

Correct Answer: A. Night Blindness

• **Night blindness (Nyctalopia)** = the earliest sign of vitamin A deficiency; retinal rod cells cannot regenerate rhodopsin (visual purple) fast enough to adapt to dim light when retinol is scarce. • **Progression** — prolonged deficiency causes xerophthalmia (dry cornea), Bitot's spots on the sclera, corneal ulceration, and ultimately irreversible blindness. • Vitamin A deficiency is the leading preventable cause of childhood blindness worldwide, affecting millions in developing countries. • 💡 Option B (Scurvy) is wrong because scurvy is caused by vitamin C deficiency and manifests as bleeding gums and impaired wound healing; Option C (Beriberi) is wrong because beriberi results from thiamine (B1) deficiency with nerve and cardiac damage; Option D (Rickets) is wrong because rickets is caused by vitamin D deficiency leading to soft, deformed bones.

Correct Answer: C. Protecting cells from damage

• **Antioxidants** = molecules (vitamins C, E, beta-carotene, polyphenols) that donate electrons to unstable free radicals, neutralizing them before they damage DNA, proteins, and cell membranes. • **Disease link** — oxidative stress from unchecked free radicals contributes to atherosclerosis, cancer, neurodegenerative diseases, and accelerated aging. • The body also produces endogenous antioxidants — superoxide dismutase, catalase, and glutathione peroxidase — that work alongside dietary ones. • 💡 Option A (Increasing blood volume) is wrong because blood volume is regulated by kidneys, aldosterone, and fluid intake, not antioxidants; Option B (Digesting proteins) is wrong because proteolysis is performed by pepsin in the stomach and proteases (trypsin, chymotrypsin) in the small intestine; Option D (Providing energy) is wrong because antioxidants function as electron donors for neutralization, not as metabolic fuels.

Correct Answer: D. Vitamin B Complex

• **Vitamin B Complex** = includes eight distinct water-soluble vitamins (B1 through B12 with gaps) that dissolve in water, cannot be stored in fatty tissues, and are rapidly excreted by the kidneys. • **Daily need** — because the body cannot accumulate reserves, consistent daily intake from whole grains, legumes, dairy, and meat is essential to prevent deficiency symptoms. • This group covers thiamine, riboflavin, niacin, pantothenic acid, B6, biotin, folate, and B12 — each with unique metabolic roles. • 💡 Option A (Vitamin D) is wrong because it is fat-soluble and stored in liver and adipose tissue for months; Option B (Vitamin E) is wrong because it is also fat-soluble and accumulates in body fat; Option C (Vitamin A) is wrong because it is fat-soluble and the liver stores enough for several months.

Correct Answer: D. Calcium

• **Calcium** = constitutes about 39% of all minerals in the body and ~99% of total body calcium is locked in the skeleton as hydroxyapatite crystals, giving bone its rigidity. • **Dynamic reservoir** — bone constantly remodels: osteoblasts deposit calcium, osteoclasts resorb it, maintaining blood calcium levels between 8.5–10.5 mg/dL. • Adults carry approximately 1 kg of calcium in their skeleton; daily requirements rise to 1,200 mg after age 50 to slow osteoporosis. • 💡 Option A (Iron) is wrong because iron is a micro-mineral found mainly in hemoglobin and myoglobin, not the skeleton; Option B (Potassium) is wrong because potassium is an intracellular electrolyte for nerve and muscle function, not a skeletal mineral; Option C (Phosphorus) is wrong because while phosphorus forms phosphate in bone alongside calcium, it is present in lower total amounts.