PCAT Biological 2 — Questions and Answers
Question 1: Which enzyme is responsible for unwinding the DNA double helix during replication?
- DNA polymerase III
- Helicase (Correct answer)
- Primase
- Ligase
Correct answer: Helicase
Helicase breaks the hydrogen bonds between base pairs to unwind the double helix at the replication fork.
Question 2: Which phase of meiosis results in the separation of homologous chromosomes?
- Meiosis II Anaphase
- Meiosis I Anaphase (Correct answer)
- Meiosis I Metaphase
- Meiosis II Metaphase
Correct answer: Meiosis I Anaphase
During Anaphase I of meiosis, homologous chromosome pairs are pulled to opposite poles, reducing the chromosome number by half.
Question 3: What is the primary function of the smooth endoplasmic reticulum?
- Protein synthesis
- Lipid synthesis and detoxification (Correct answer)
- Packaging proteins for secretion
- DNA replication
Correct answer: Lipid synthesis and detoxification
The smooth ER lacks ribosomes and is specialized for lipid synthesis, steroid hormone production, and detoxification of drugs.
Question 4: In a dihybrid cross between two AaBb parents, what fraction of offspring will be aabb?
- 1/4
- 1/8
- 1/16 (Correct answer)
- 3/16
Correct answer: 1/16
Each trait independently assorts; the probability of aa is 1/4 and bb is 1/4, so aabb = 1/4 × 1/4 = 1/16.
Question 5: Which blood vessel carries oxygenated blood from the lungs to the heart?
- Pulmonary artery
- Pulmonary vein (Correct answer)
- Aorta
- Superior vena cava
Correct answer: Pulmonary vein
The pulmonary veins carry oxygenated blood from the lungs back to the left atrium of the heart.
Question 6: Which type of RNA carries the genetic code from the nucleus to the ribosome?
- tRNA
- rRNA
- mRNA (Correct answer)
- snRNA
Correct answer: mRNA
Messenger RNA (mRNA) is transcribed from DNA in the nucleus and carries the codon sequence to the ribosome for translation.
Question 7: Which organelle is the primary site of ATP production via aerobic respiration?
- Nucleus
- Lysosome
- Golgi apparatus
- Mitochondria (Correct answer)
Correct answer: Mitochondria
Mitochondria house the electron transport chain and ATP synthase, generating the majority of ATP through oxidative phosphorylation.
PCAT Biological 2
Which enzyme is responsible for unwinding the DNA double helix during replication?