GACE Biology 3 — Questions and Answers
Question 1: In the light-dependent reactions of photosynthesis, which molecule serves as the primary electron donor, releasing oxygen as a byproduct?
- NADPH
- Water (Correct answer)
- Carbon dioxide
- Glucose
Correct answer: Water
Water molecules are split by photosystem II (photolysis), donating electrons to replace those lost by chlorophyll and releasing O₂ as a byproduct.
Question 2: Which of the following best describes the role of transfer RNA (tRNA) during translation?
- Carries genetic instructions from the nucleus to the ribosome
- Catalyzes peptide bond formation between amino acids
- Delivers specific amino acids to the ribosome based on codon-anticodon matching (Correct answer)
- Processes pre-mRNA by removing introns
Correct answer: Delivers specific amino acids to the ribosome based on codon-anticodon matching
tRNA molecules carry specific amino acids and use their anticodon loops to recognize complementary codons on mRNA, ensuring correct amino acid incorporation.
Question 3: A species of fish living in a deep ocean trench has evolved bioluminescent lures. This is an example of which evolutionary concept?
- Convergent evolution (Correct answer)
- Adaptive radiation
- Coevolution
- Allopatric speciation
Correct answer: Convergent evolution
Convergent evolution occurs when unrelated organisms independently evolve similar traits in response to similar environmental pressures, such as luminescent lures in different deep-sea lineages.
Question 4: Which level of protein structure is maintained primarily by hydrogen bonds between backbone amino and carbonyl groups, producing alpha helices and beta sheets?
- Primary structure
- Secondary structure (Correct answer)
- Tertiary structure
- Quaternary structure
Correct answer: Secondary structure
Secondary structure refers to local folding patterns (alpha helices and beta sheets) stabilized by hydrogen bonds between backbone peptide groups.
Question 5: Which type of symbiosis describes a relationship in which one organism benefits and the other is neither harmed nor helped?
- Mutualism
- Parasitism
- Commensalism (Correct answer)
- Competition
Correct answer: Commensalism
Commensalism describes a symbiotic relationship where one species benefits while the other experiences no significant positive or negative effect.
Question 6: A student crosses two heterozygous pea plants (Tt × Tt). What fraction of offspring is expected to be heterozygous?
- 1/4
- 1/2 (Correct answer)
- 3/4
- All offspring
Correct answer: 1/2
A Tt × Tt cross yields a 1:2:1 ratio (1 TT : 2 Tt : 1 tt), so 2/4 = 1/2 of offspring are heterozygous.
Question 7: Which process in the nitrogen cycle converts atmospheric N₂ into ammonia (NH₃), making nitrogen available to plants?
- Nitrification
- Denitrification
- Nitrogen fixation (Correct answer)
- Ammonification
Correct answer: Nitrogen fixation
Nitrogen fixation, carried out by organisms like Rhizobium bacteria, converts inert atmospheric N₂ into ammonia that plants can absorb and use.
GACE Biology 3
In the light-dependent reactions of photosynthesis, which molecule serves as the primary electron donor, releasing oxygen as a byproduct?