GED SCIENCE EXAM QUESTION AND ANSWERS
WITH RATIONALE GRADED A+
1. A cell has many small, membrane‐bound vesicles filled with hydrolytic enzymes and
lacks a cell wall. Which organelle is observed?
o A. Chloroplast
o B. Mitochondrion
o C. Lysosome
o D. Endoplasmic reticulum
Answer: C. Lysosome
Rationale: Lysosomes are small vesicles of digestive enzymes. Chloroplasts only
occur in plant cells (no cell wall in this cell), mitochondria produce energy but are
not “small vesicles,” and the ER is a network of tubules, not discrete vesicles.
Cell Organelle Identification
2. Aquatic plants under varying light intensities produce the following O₂:
Light (μmol·m⁻²·s⁻¹) O₂ (mL/hr)
50 1.8
100 3.6
200 6.0
400 7.2
800 7.5
What conclusion?
o A. Rate increases linearly at all intensities.
o B. Rate plateaus above 200 due to another limit.
o C. Rate decreases after 200 because of photoinhibition.
o D. Rate highest at 50 then declines.
Answer: B. Rate plateaus above 200 due to another limit.
Rationale: O₂ rises between 50→200, then levels off (200→800). It does not
decline (ruling out C). A is false (not linear), D is false (rate at 50 is lowest).
Photosynthesis Rate vs. Light Intensity
,3. Two heterozygous (Aa) pea plants cross. Probability of an Aa offspring?
o A. 25%
o B. 50%
o C. 75%
o D. 100%
Answer: B. 50%
Rationale: Punnett square Aa×Aa yields AA 25%, Aa 50%, aa 25%. Only 50%
are Aa. 25% (A) is AA or aa; 75% (C) is purple flower (AA + Aa), not strictly
heterozygous. Mendelian Genetics
4. In polluted cities, dark‐winged moths (D) increase from 50% to 90%. Best explanation?
o A. Genetic drift
o B. Artificial selection
o C. Natural selection
o D. Gene flow
Answer: C. Natural selection
Rationale: Predators more easily spot light moths against soot, so dark moths
survive and reproduce. It is non‐random environmental selection. Genetic drift is
random; artificial selection involves humans; gene flow involves migration.
Natural Selection: Peppered Moths
5. During exercise, heart rate and breathing both increase to deliver oxygen. Which two
systems?
o A. Skeletal & endocrine
o B. Circulatory & respiratory
o C. Digestive & nervous
o D. Lymphatic & excretory
Answer: B. Circulatory & respiratory
Rationale: The respiratory system brings O₂ into lungs; circulatory transports O₂
in blood. Skeletal/endocrine do not directly move oxygen; digestive breaks down
food; lymphatic/excretory are for immune and waste removal. Human Body
Systems
6.
A lake’s large‐fish population falls 60% while plankton double. Likely cause?
o A. Overfishing small fish (zooplankton decline).
, o B. Eagle disease (less predation on large fish).
o C. Nutrient runoff → algal bloom (plankton ↑, fish die from hypoxia).
o D. Invasive snails ↑ zooplankton.
Answer: C. Nutrient runoff → algal bloom (plankton ↑, fish die from
hypoxia).
Rationale: Excess nutrients cause phytoplankton bloom, then oxygen depletion
kills fish. A would reduce zooplankton; B would increase large fish; D has no
direct mechanism for plankton doubling. Predator‐Prey Dynamics
7. Germinating seeds produce CO₂: at 10 °C = 1.0 mL/hr; 20 °C = 2.5 mL/hr; 30 °C = 4.8
mL/hr; 40 °C = 5.0 mL/hr. Greatest proportional increase?
o A. 10→20 °C
o B. 20→30 °C
o C. 30→40 °C
o D. All equal
Answer: A. 10→20 °C
Rationale: Proportional increase = (2.5–1.0)/1.0 = 150%. From 20→30: (4.8–
2.5)/2.5 = 92%; 30→40: (5.0–4.8)/4.8 ≈ 4%. So 10→20 is highest. Cellular
Respiration vs. Temperature
8.
After an influenza vaccine, which cell type immediately produces antibodies?
o A. T helper cells
o B. B plasma cells
o C. Memory T cells
o D. Macrophages
Answer: B. B plasma cells
Rationale: B cells differentiate into plasma cells that secrete antibodies. T helper
cells assist activation; memory T cells do not secrete antibodies; macrophages
engulf pathogens, not secrete antibodies. Immune Response
9.
An organism has a chitinous exoskeleton, segmented body, and jointed legs, and molts to
grow. Which phylum?
o A. Mollusca
o B. Annelida
o C. Arthropoda
, o D. Platyhelminthes
Answer: C. Arthropoda
Rationale: Arthropods have chitinous exoskeletons, segmented bodies, and
jointed appendages. Mollusks have shells, not jointed legs; annelids are soft‐
bodied worms; flatworms are unsegmented, soft. Taxonomic Classification
10. Which best describes nitrogen‐fixing bacteria’s role?
o A. Convert atmospheric N₂ → NH₃ usable by plants.
o B. Oxidize NH₃ → NO₃⁻ for plants.
o C. Convert organic nitrogen → N₂.
o D. Fix nitrates into amino acids in plant leaves.
Answer: A. Convert atmospheric N₂ → NH₃ usable by plants.
Rationale: Nitrogenase in bacteria reduces N₂ to NH₃. Oxidizing NH₃ → NO₃⁻ is
nitrification (nitrifiers). Converting organic N → N₂ is denitrification. Plants, not
bacteria, incorporate nitrates into amino acids. Nitrogen Fixation
11. During which phase of mitosis do sister chromatids separate and move to opposite poles?
o A. Prophase
o B. Metaphase
o C. Anaphase
o D. Telophase
Answer: C. Anaphase
Rationale: In anaphase, centromeres split and chromatids move apart. Prophase
condenses chromosomes; metaphase aligns them at the equator; telophase re‐
forms nuclear envelopes. Cell Cycle and Mitosis
12. An enzyme’s activity peaks at pH 7, then drops off at pH 5 and pH 9. Why?
o A. Substrate is absent outside pH 7.
o B. Enzyme denatures when pH differs from optimum.
o C. Product feedback inhibition occurs.
o D. Temperature changes with pH.
Answer: B. Enzyme denatures when pH differs from optimum.
Rationale: Enzyme tertiary structure is pH‐sensitive; extremes disrupt active site.
Substrate presence does not depend solely on pH; feedback inhibition is related to
product concentration; temperature isn’t tied directly to pH. Enzyme Activity vs.
WITH RATIONALE GRADED A+
1. A cell has many small, membrane‐bound vesicles filled with hydrolytic enzymes and
lacks a cell wall. Which organelle is observed?
o A. Chloroplast
o B. Mitochondrion
o C. Lysosome
o D. Endoplasmic reticulum
Answer: C. Lysosome
Rationale: Lysosomes are small vesicles of digestive enzymes. Chloroplasts only
occur in plant cells (no cell wall in this cell), mitochondria produce energy but are
not “small vesicles,” and the ER is a network of tubules, not discrete vesicles.
Cell Organelle Identification
2. Aquatic plants under varying light intensities produce the following O₂:
Light (μmol·m⁻²·s⁻¹) O₂ (mL/hr)
50 1.8
100 3.6
200 6.0
400 7.2
800 7.5
What conclusion?
o A. Rate increases linearly at all intensities.
o B. Rate plateaus above 200 due to another limit.
o C. Rate decreases after 200 because of photoinhibition.
o D. Rate highest at 50 then declines.
Answer: B. Rate plateaus above 200 due to another limit.
Rationale: O₂ rises between 50→200, then levels off (200→800). It does not
decline (ruling out C). A is false (not linear), D is false (rate at 50 is lowest).
Photosynthesis Rate vs. Light Intensity
,3. Two heterozygous (Aa) pea plants cross. Probability of an Aa offspring?
o A. 25%
o B. 50%
o C. 75%
o D. 100%
Answer: B. 50%
Rationale: Punnett square Aa×Aa yields AA 25%, Aa 50%, aa 25%. Only 50%
are Aa. 25% (A) is AA or aa; 75% (C) is purple flower (AA + Aa), not strictly
heterozygous. Mendelian Genetics
4. In polluted cities, dark‐winged moths (D) increase from 50% to 90%. Best explanation?
o A. Genetic drift
o B. Artificial selection
o C. Natural selection
o D. Gene flow
Answer: C. Natural selection
Rationale: Predators more easily spot light moths against soot, so dark moths
survive and reproduce. It is non‐random environmental selection. Genetic drift is
random; artificial selection involves humans; gene flow involves migration.
Natural Selection: Peppered Moths
5. During exercise, heart rate and breathing both increase to deliver oxygen. Which two
systems?
o A. Skeletal & endocrine
o B. Circulatory & respiratory
o C. Digestive & nervous
o D. Lymphatic & excretory
Answer: B. Circulatory & respiratory
Rationale: The respiratory system brings O₂ into lungs; circulatory transports O₂
in blood. Skeletal/endocrine do not directly move oxygen; digestive breaks down
food; lymphatic/excretory are for immune and waste removal. Human Body
Systems
6.
A lake’s large‐fish population falls 60% while plankton double. Likely cause?
o A. Overfishing small fish (zooplankton decline).
, o B. Eagle disease (less predation on large fish).
o C. Nutrient runoff → algal bloom (plankton ↑, fish die from hypoxia).
o D. Invasive snails ↑ zooplankton.
Answer: C. Nutrient runoff → algal bloom (plankton ↑, fish die from
hypoxia).
Rationale: Excess nutrients cause phytoplankton bloom, then oxygen depletion
kills fish. A would reduce zooplankton; B would increase large fish; D has no
direct mechanism for plankton doubling. Predator‐Prey Dynamics
7. Germinating seeds produce CO₂: at 10 °C = 1.0 mL/hr; 20 °C = 2.5 mL/hr; 30 °C = 4.8
mL/hr; 40 °C = 5.0 mL/hr. Greatest proportional increase?
o A. 10→20 °C
o B. 20→30 °C
o C. 30→40 °C
o D. All equal
Answer: A. 10→20 °C
Rationale: Proportional increase = (2.5–1.0)/1.0 = 150%. From 20→30: (4.8–
2.5)/2.5 = 92%; 30→40: (5.0–4.8)/4.8 ≈ 4%. So 10→20 is highest. Cellular
Respiration vs. Temperature
8.
After an influenza vaccine, which cell type immediately produces antibodies?
o A. T helper cells
o B. B plasma cells
o C. Memory T cells
o D. Macrophages
Answer: B. B plasma cells
Rationale: B cells differentiate into plasma cells that secrete antibodies. T helper
cells assist activation; memory T cells do not secrete antibodies; macrophages
engulf pathogens, not secrete antibodies. Immune Response
9.
An organism has a chitinous exoskeleton, segmented body, and jointed legs, and molts to
grow. Which phylum?
o A. Mollusca
o B. Annelida
o C. Arthropoda
, o D. Platyhelminthes
Answer: C. Arthropoda
Rationale: Arthropods have chitinous exoskeletons, segmented bodies, and
jointed appendages. Mollusks have shells, not jointed legs; annelids are soft‐
bodied worms; flatworms are unsegmented, soft. Taxonomic Classification
10. Which best describes nitrogen‐fixing bacteria’s role?
o A. Convert atmospheric N₂ → NH₃ usable by plants.
o B. Oxidize NH₃ → NO₃⁻ for plants.
o C. Convert organic nitrogen → N₂.
o D. Fix nitrates into amino acids in plant leaves.
Answer: A. Convert atmospheric N₂ → NH₃ usable by plants.
Rationale: Nitrogenase in bacteria reduces N₂ to NH₃. Oxidizing NH₃ → NO₃⁻ is
nitrification (nitrifiers). Converting organic N → N₂ is denitrification. Plants, not
bacteria, incorporate nitrates into amino acids. Nitrogen Fixation
11. During which phase of mitosis do sister chromatids separate and move to opposite poles?
o A. Prophase
o B. Metaphase
o C. Anaphase
o D. Telophase
Answer: C. Anaphase
Rationale: In anaphase, centromeres split and chromatids move apart. Prophase
condenses chromosomes; metaphase aligns them at the equator; telophase re‐
forms nuclear envelopes. Cell Cycle and Mitosis
12. An enzyme’s activity peaks at pH 7, then drops off at pH 5 and pH 9. Why?
o A. Substrate is absent outside pH 7.
o B. Enzyme denatures when pH differs from optimum.
o C. Product feedback inhibition occurs.
o D. Temperature changes with pH.
Answer: B. Enzyme denatures when pH differs from optimum.
Rationale: Enzyme tertiary structure is pH‐sensitive; extremes disrupt active site.
Substrate presence does not depend solely on pH; feedback inhibition is related to
product concentration; temperature isn’t tied directly to pH. Enzyme Activity vs.
