General Science MCQ Practice

• The ionosphere is a layer with ionized gases that can reflect certain radio waves back to Earth, enabling long-distance radio communication.
• Key concept: plasma/ionization enables reflection; the “critical frequency” determines which frequencies are reflected.
• Formula (brief): f_c ≈ 9√N_e, where f_c is the critical frequency and N_e is electron density (in appropriate units).
• Why others are incorrect: Exosphere, Troposphere, and Stratosphere are not primarily reflective ionized layers for radio waves.
• Exam tip: Shortwave radio relies on ionospheric reflection for skywave propagation.

• Key concept: Sanger sequencing uses dideoxynucleotide chain termination (Sanger method) to read DNA sequences.
• Why this is correct: Frederick Sanger developed the first reliable DNA sequencing method in 1977, enabling precise base-by-base reading of DNA.
• Brief logic: The method relies on labeled chain-terminating nucleotides to create fragments that, when separated, reveal the sequence.
• Why others are incorrect: - A: Khorana helped in nucleotide synthesis, not sequencing technique’s invention. - B: Watson-Crick described DNA structure, not sequencing method. - D: E. M. Southern developed the Southern blot technique for detecting DNA, not sequencing.

Exam tip: Remember “Sanger = sequencing method (chain termination).”

• Key concept: The biosphere includes all living organisms and the zones they inhabit on Earth.
• Reason: Life exists in all regions where organisms can survive, from soil and water to air, linking all ecosystems.
• Why other options are incorrect: < ul>
• Lithosphere = solid Earth’s crust and upper mantle, not specifically life-bearing.
• Hydrosphere = all water bodies, not limited to life, though essential for it.
• Atmosphere = gases around Earth; supports life but does not inherently denote life-bearing regions.

Exam tip: Remember biosphere = “life-containing” layer; adjacent spheres influence each other through ecosystems.

• Why: Electric current is the flow of charged particles through a conductor. In metallic wires, the mobile charge carriers are electrons, so their movement constitutes current.

• Reason: Cerebral malaria is caused by Plasmodium falciparum due to its infected red blood cells sticking to brain vessels (sequestration) via PfEMP1 proteins, leading to brain injury.
• Key concept: PfEMP1-mediated cytoadherence causes microvascular obstruction and cerebral symptoms.
• Tip: In exams, note that falciparum malaria is the only species commonly causing cerebral malaria and severe disease.
• Why others are incorrect: P. vivax and P. malariae cause milder disease; they rarely cause cerebral malaria.

• Why: Adult filarial worms reside in the human lymphatic system (lymphatics), especially in lymphatic vessels and nodes.
• Key concept: Filarial parasites migrate through lymphatics; block flow causes swelling (lymphoedema/elephantiasis).
• Why others are wrong:
  • A. Blood – adults do not live primarily in blood vessels.
  • C. Liver – not the primary habitat for adult worms.
  • D. Intestine – not the site for adult filariae.
• Exam tip: Recall filariae causing lymphatic filariasis affects lymphatic drainage; focus on symptoms like limb swelling.

• Reason: ADH (vasopressin) regulates water reabsorption in kidneys. Lack of ADH leads to excessive dilute urine and thirst.
• Key concept: Deficiency or insensitivity to ADH causes polyuria and polydipsia.
• Formula/numerical logic: Urine osmolarity decreases with ADH deficiency; plasma osmolality rises, triggering thirst.
• Why others’re incorrect: - Diabetes mellitus: hormone insulin issue, high blood glucose.
- Grave's disease: hyperthyroidism autoimmune. - Cushing's disease: excess cortisol.

• Explanation: Aves (birds) are not living in marine water as a primary habitat. Although some birds feed near/coastlines or swim, birds are air-breathing vertebrates adapted to land and air, not true marine life. Other groups include species that routinely inhabit marine waters: mammals (e.g., whales, seals), amphibians (some frogs breed in water bodies), and reptiles (e.g., sea turtles, marine iguanas).
• Key concept: Habitat adaptation and ecological niche; marine life includes groups with specialized marine adaptations.
• Exam tip: If the option mentions a group typically terrestrial or aerial, check whether there are true marine inhabitants; birds are the exception here.

• Normal human blood is alkaline, with a pH around 7.35–7.45. This slight alkalinity is maintained by buffering systems (bicarbonate, proteins) and respiration.
• Key concept: pH scale and homeostasis in blood; the body keeps pH within a narrow range necessary for enzyme activity.
• Quick check: If pH < 7.35 → acidity; if pH > 7.45 → alkalosis.
• Exam tip: Remember “7.35–7.45” as the normal blood pH range.
• Why others are incorrect: A = acidic (pH < 7.0), C = neutral (pH ≈ 7.0), D = variable (pH is tightly regulated).

• Reason: Whales are mammals; they breathe air via lungs. The lungs exchange oxygen with blood through alveoli, not gills or skin.
• Why others are wrong: - Integuments: skin/outer covering, not a respiratory organ. - Gills: used by fish, not mammals like whales. - Trachea: airway leading to lungs, not the main site of gas exchange.
• Key concept: Mammalian respiration relies on lungs and alveolar gas exchange (O2 in, CO2 out).
• Exam tip: If the organism is a mammal, choose lungs; if it’s an aquatic fish, consider gills.