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MCQ Practice

General Science (Everyday Science) MCQs

A keystone species is one whose removal causes:

  • A. No measurable ecological change
  • B. A disproportionately large effect on community structure
  • C. Only a reduction in primary productivity
  • D. Immediate extinction of all species
Explanation:
Keystone species have ecological impacts much larger than expected from their abundance.

Genetic drift is strongest in populations that are:

  • A. Infinitely large
  • B. Very small
  • C. Perfectly mixed and enormous
  • D. Under no mutation
Explanation:
Random allele-frequency changes are amplified when sample sizes are small.

Natural selection acts directly on:

  • A. Genotypes only
  • B. Phenotypes affecting fitness
  • C. Mutations before expression
  • D. Species as indivisible units only
Explanation:
Selection filters expressed traits that influence survival and reproduction.

Action potentials in neurons propagate because of sequential opening of:

  • A. Ligand-gated chloride channels only
  • B. Voltage-gated sodium and potassium channels
  • C. Aquaporins
  • D. Calcium pumps only
Explanation:
Depolarization and repolarization are driven mainly by voltage-gated Na(^+) and K(^+) channels.

Which immune cells differentiate into plasma cells that secrete antibodies?

  • A. T helper cells
  • B. Cytotoxic T cells
  • C. B lymphocytes
  • D. Macrophages
Explanation:
Activated B cells become antibody-producing plasma cells.

Hemoglobin’s oxygen affinity is decreased by lower pH due to the:

  • A. Pasteur effect
  • B. Bohr effect
  • C. Warburg effect
  • D. Haldane law of diffusion
Explanation:
Protonation stabilizes deoxyhemoglobin, promoting oxygen release in acidic tissues.

In mammals, most nutrient absorption occurs in the:

  • A. Stomach
  • B. Large intestine
  • C. Small intestine
  • D. Esophagus
Explanation:
The small intestine’s villi and microvilli maximize absorptive surface area.

Stomata primarily regulate:

  • A. Seed dispersal
  • B. Gas exchange and transpiration
  • C. Protein synthesis
  • D. Root pressure directly only
Explanation:
Guard cells control stomatal aperture for (CO_2), (O_2), and water vapor exchange.

Which tissue transports sugars in vascular plants?

  • A. Xylem
  • B. Phloem
  • C. Epidermis
  • D. Cambium only
Explanation:
Phloem conducts photosynthates from sources to sinks.

Competitive inhibition usually increases the apparent:

  • A. (V_{max}) only
  • B. (K_m) without changing (V_{max})
  • C. (V_{max}) and decreases (K_m)
  • D. Catalytic constant irreversibly
Explanation:
A competitive inhibitor reduces apparent substrate affinity but can be overcome at high substrate concentration.