PCAT Biological 4 — Questions and Answers
Question 1: A mutation that converts a codon to a stop codon is best described as a:
- Missense mutation
- Silent mutation
- Nonsense mutation (Correct answer)
- Frameshift mutation
Correct answer: Nonsense mutation
A nonsense mutation changes an amino acid codon to a premature stop codon, resulting in a truncated, usually nonfunctional protein.
Question 2: Which of the following is an example of negative feedback in the human body?
- Oxytocin release during childbirth intensifying contractions
- Platelet activation attracting more platelets to a wound
- High blood glucose triggering insulin release to lower glucose (Correct answer)
- Fever increasing metabolic rate further elevating temperature
Correct answer: High blood glucose triggering insulin release to lower glucose
Insulin release in response to high blood glucose reduces glucose levels, which then signals decreased insulin release—a classic negative feedback loop.
Question 3: Which of the following correctly pairs an organelle with its function?
- Ribosome — lipid packaging for export
- Lysosome — ATP synthesis
- Peroxisome — breakdown of fatty acids and detoxification of H2O2 (Correct answer)
- Centrosome — protein glycosylation
Correct answer: Peroxisome — breakdown of fatty acids and detoxification of H2O2
Peroxisomes contain oxidative enzymes for fatty acid beta-oxidation and catalase to decompose the resulting hydrogen peroxide.
Question 4: What is the significance of the ABO blood group system in pharmacology and medicine?
- It determines drug metabolism speed
- It dictates kidney filtration rate
- Mismatched transfusions trigger complement-mediated hemolysis (Correct answer)
- It regulates neurotransmitter receptor sensitivity
Correct answer: Mismatched transfusions trigger complement-mediated hemolysis
Transfusing incompatible ABO blood types causes recipient antibodies to activate complement, lysing donor red blood cells and potentially causing fatal hemolytic transfusion reactions.
Question 5: Which property of DNA allows it to serve as a template for its own replication?
- Its single-stranded structure
- Complementary base pairing between antiparallel strands (Correct answer)
- The presence of uracil instead of thymine
- Phosphodiester bonds within a single strand
Correct answer: Complementary base pairing between antiparallel strands
Complementary base pairing (A-T, G-C) between antiparallel strands means each strand can serve as a precise template for synthesizing a new complementary strand.
Question 6: Which type of epithelium lines the alveoli to facilitate gas exchange?
- Stratified squamous epithelium
- Pseudostratified columnar epithelium
- Simple squamous epithelium (Correct answer)
- Transitional epithelium
Correct answer: Simple squamous epithelium
Simple squamous epithelium is extremely thin, providing a minimal diffusion distance for O2 and CO2 exchange between alveolar air and blood.
Question 7: What is the function of the myelin sheath surrounding axons?
- Synthesizes neurotransmitters for synaptic vesicles
- Provides metabolic energy directly to the axon
- Increases the speed of action potential conduction via saltatory conduction (Correct answer)
- Anchors the neuron to the extracellular matrix
Correct answer: Increases the speed of action potential conduction via saltatory conduction
Myelin insulates axon segments, forcing action potentials to jump between nodes of Ranvier (saltatory conduction), dramatically increasing transmission speed.
PCAT Biological 4
A mutation that converts a codon to a stop codon is best described as a: