Egyptian STEM Schools Admissions Assessment · STEM Sciences

Biological Systems and Scientific Inquiry

69 practice questions, each with the answer and an explanation.

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Random questions from this topic, one at a time. You see the answer and the explanation straight after each one.

All 69 questions

  1. In a controlled scientific experiment designed to test the effect of nitrogen fertilizer concentration on tomato plant growth rate, which variable must be held constant across all experimental groups?
  2. Which organelle in eukaryotic plant cells contains chlorophyll and carries out the light-dependent reactions of photosynthesis within its thylakoid membranes?
  3. In a monohybrid Mendelian cross between two heterozygous tall pea plants (), what is the expected phenotypic ratio of tall to dwarf offspring?
  4. During which phase of cellular mitosis do sister chromatids separate at their centromeres and migrate toward opposite spindle poles?
  5. What is the net yield of ATP molecules generated per molecule of glucose during anaerobic glycolysis in the cytoplasm?
  6. Which base is found in RNA molecules in place of the thymine () present in DNA?
  7. A student observes that enzyme activity peaks at and declines rapidly above . What molecular mechanism causes this abrupt decline in activity at elevated temperatu…
  8. Which ecological level of organization encompasses all interacting populations of different species inhabiting a defined geographic area at the same time?
  9. What is the primary role of the stomata and surrounding guard cells on the underside of plant leaves?
  10. Which human blood type is considered the universal red blood cell donor because its erythrocytes lack both A and B surface antigens?
  11. What process produces genetic variation during Prophase I of meiosis by exchanging genetic material between non-sister chromatids of homologous chromosomes?
  12. Which biological macromolecule functions as the primary structural component of plant cell walls, consisting of unbranched linear chains of -D-glucose linked by glycosidic bonds…
  13. In negative feedback regulation of human blood glucose, which hormone is secreted by the beta cells of the pancreatic islets in response to elevated blood sugar?
  14. A DNA strand has the nucleotide sequence . What is the complementary sequence on the antiparallel strand?
  15. Which kingdom in Whittaker's five-kingdom biological classification system comprises heterotrophic eukaryotic organisms with chitinous cell walls that absorb nutrients via external enzymatic digestion…
  16. What is the term for a symbiotic relationship in which one organism benefits while the other organism is neither helped nor harmed?
  17. Which cellular transport mechanism moves molecules across a plasma membrane against their concentration gradient using metabolic energy derived from ATP hydrolysis?
  18. What evolutionary mechanism describes changes in allele frequencies within a small population caused purely by random chance events rather than natural selection?
  19. Which chamber of the human heart pumps oxygenated blood under high systemic arterial pressure into the aorta?
  20. Which enzyme unzips and unwinds the double-stranded DNA helix at the replication fork during DNA replication?
  21. What is the primary function of ribosomes in all living cells?
  22. In a food web, why does available energy diminish by approximately 90% at each successive trophic level (the 10% rule)?
  23. What type of natural selection favors intermediate phenotypes while selecting against both extreme phenotypic variations, reducing genetic variance in a population?
  24. Which cellular junction forms an impermeable water-tight seal between adjacent epithelial cells, preventing intercellular leakage of fluids and solutes?
  25. In human genetics, a father with red-green color blindness (an X-linked recessive trait) and a homozygous normal mother have children. What is the probability that their son will be color blind?
  26. Which step of the scientific method directly follows the formulation of a testable hypothesis?
  27. In Michaelis-Menten enzyme kinetics, when substrate concentration , what fraction of the maximum reaction velocity is achieved?
  28. A parallel-plate capacitor has capacitance charged to . If the plate separation is doubled while disconnected from the battery, what is the new stored energy?
  29. Water flows through a horizontal pipe with cross-sectional area at speed . At a constriction, area is . What is the pressure drop…
  30. A car negotiates an unbanked circular curve of radius . If the coefficient of static friction is (take ), what is the maximum speed without skiddi…
  31. What is the half-life of a first-order chemical reaction if the rate constant is ?
  32. What does active transport require that diffusion does not?
  33. What is the movement of water across a partially permeable membrane from a dilute to a concentrated solution called?
  34. What does meiosis produce from one diploid cell?
  35. One bacterial cell divides by binary fission every 20 minutes. How many cells are there after 7 divisions, starting from one cell?
  36. A cross produces phenotypes in the ratio 3:4. Out of 154 offspring, how many are expected in the second class?
  37. A coding region of mRNA is 417 nucleotides long (excluding the stop codon). How many amino acids does it code for?
  38. A cell measures 2 μm in reality. In a micrograph it measures 0.1 mm. What is the magnification? (1 mm = 1000 μm)
  39. A coding region of mRNA is 519 nucleotides long (excluding the stop codon). How many amino acids does it code for?
  40. A cross produces phenotypes in the ratio 3:7. Out of 370 offspring, how many are expected in the second class?
  41. In a population in Hardy–Weinberg equilibrium, 9% of individuals show a recessive trait. What proportion are heterozygous carriers?
  42. What is the surface-area-to-volume ratio of a cube-shaped cell of side 3 μm?
  43. Which part of the blood carries most of the oxygen?
  44. Which tissue carries sugars from the leaves to the rest of a plant?
  45. A coding region of mRNA is 63 nucleotides long (excluding the stop codon). How many amino acids does it code for?
  46. Why do antibiotics not cure viral infections?
  47. Which organ produces insulin?
  48. A cross produces phenotypes in the ratio 7:4. Out of 363 offspring, how many are expected in the second class?
  49. In pea plants, tall (T) is dominant to short (t). A TT plant is crossed with a Tt plant. What is the probability that an offspring is homozygous dominant (TT)?
  50. In a sample of double-stranded DNA, 35% of the bases are adenine. What percentage are guanine?
  51. A cell measures 50 μm in reality. In a micrograph it measures 5 mm. What is the magnification? (1 mm = 1000 μm)
  52. A cross produces phenotypes in the ratio 3:7. Out of 250 offspring, how many are expected in the second class?
  53. A food chain is grass → grasshopper → frog → snake. If the grass fixes 10000 kJ and about 10% of energy passes up each level, how much energy reaches the snake?
  54. A cell measures 10 μm in reality. In a micrograph it measures 0.5 mm. What is the magnification? (1 mm = 1000 μm)
  55. Which enzyme in saliva starts the digestion of starch?
  56. How many chromosomes are in a normal human body cell?
  57. A cross produces phenotypes in the ratio 8:4. Out of 324 offspring, how many are expected in the second class?
  58. In pea plants, tall (T) is dominant to short (t). A Tt plant is crossed with a Tt plant. What is the probability that an offspring is homozygous recessive (tt)?
  59. In a population in Hardy–Weinberg equilibrium, 4% of individuals show a recessive trait. What proportion are heterozygous carriers?
  60. In a population in Hardy–Weinberg equilibrium, 1% of individuals show a recessive trait. What proportion are heterozygous carriers?
  61. Which organisms recycle nutrients by breaking down dead matter?
  62. In pea plants, tall (T) is dominant to short (t). A Tt plant is crossed with a tt plant. What is the probability that an offspring is heterozygous (Tt)?
  63. What is the surface-area-to-volume ratio of a cube-shaped cell of side 4 μm?
  64. A coding region of mRNA is 60 nucleotides long (excluding the stop codon). How many amino acids does it code for?
  65. Which part of the kidney filters the blood?
  66. In a sample of double-stranded DNA, 34% of the bases are adenine. What percentage are guanine?
  67. Which type of blood vessel carries blood away from the heart?
  68. A coding region of mRNA is 507 nucleotides long (excluding the stop codon). How many amino acids does it code for?
  69. In a population in Hardy–Weinberg equilibrium, 36% of individuals show a recessive trait. What proportion are heterozygous carriers?

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