PCAT Biology 2 — Questions and Answers
Question 1: Which organelle is primarily responsible for producing ATP through oxidative phosphorylation?
- Endoplasmic reticulum
- Mitochondria (Correct answer)
- Golgi apparatus
- Lysosome
Correct answer: Mitochondria
Mitochondria generate ATP via oxidative phosphorylation in their inner membrane through the electron transport chain and ATP synthase.
Question 2: During meiosis II, which event separates sister chromatids?
- Crossing over
- Synapsis
- Anaphase II (Correct answer)
- Metaphase I
Correct answer: Anaphase II
During Anaphase II, cohesins break down and sister chromatids are pulled to opposite poles of the cell.
Question 3: What type of RNA carries amino acids to the ribosome during translation?
- mRNA
- rRNA
- tRNA (Correct answer)
- snRNA
Correct answer: tRNA
Transfer RNA (tRNA) carries specific amino acids and matches them to codons on mRNA via its anticodon loop.
Question 4: The sodium-potassium pump moves ions against their concentration gradient using which energy source?
- GTP hydrolysis
- ATP hydrolysis (Correct answer)
- Proton motive force
- NADH oxidation
Correct answer: ATP hydrolysis
The Na⁺/K⁺-ATPase uses ATP hydrolysis to pump 3 Na⁺ out and 2 K⁺ into the cell against their gradients.
Question 5: Which type of mutation results in a premature stop codon?
- Silent mutation
- Missense mutation
- Nonsense mutation (Correct answer)
- Frameshift mutation
Correct answer: Nonsense mutation
A nonsense mutation changes an amino acid codon into a stop codon (UAA, UAG, or UGA), prematurely terminating translation.
Question 6: In which phase of the cell cycle does DNA replication occur?
- G1 phase
- S phase (Correct answer)
- G2 phase
- M phase
Correct answer: S phase
DNA synthesis (replication) occurs during the S (synthesis) phase of interphase, duplicating the genome before cell division.
Question 7: Which immunoglobulin class is the most abundant in serum and provides long-term immunity?
- IgA
- IgE
- IgM
- IgG (Correct answer)
Correct answer: IgG
IgG is the most abundant serum antibody (~75%), crosses the placenta, and provides long-lasting humoral immunity after infection or vaccination.
PCAT Biology 2
Which organelle is primarily responsible for producing ATP through oxidative phosphorylation?