PCAT Biology 4 — Questions and Answers
Question 1: Which type of epithelium lines the inner surface of blood vessels?
- Stratified squamous epithelium
- Simple columnar epithelium
- Simple cuboidal epithelium
- Simple squamous epithelium (Correct answer)
Correct answer: Simple squamous epithelium
Simple squamous epithelium (endothelium) lines blood vessels, allowing efficient diffusion and forming a smooth surface that reduces friction.
Question 2: In the lac operon of E. coli, what role does the repressor protein play in the absence of lactose?
- It activates RNA polymerase binding
- It blocks the operator preventing transcription (Correct answer)
- It degrades the mRNA produced
- It phosphorylates the promoter region
Correct answer: It blocks the operator preventing transcription
In the absence of lactose (the inducer), the repressor binds the operator sequence and prevents RNA polymerase from transcribing the structural genes.
Question 3: Which phase of mitosis is characterized by chromosomes aligning at the cell's equatorial plate?
- Prophase
- Metaphase (Correct answer)
- Anaphase
- Telophase
Correct answer: Metaphase
During metaphase, chromosomes align at the metaphase plate (cell equator) with spindle fibers attached to each sister chromatid's kinetochore.
Question 4: Which hormone is produced by the posterior pituitary and triggers uterine contractions during labor?
- Prolactin
- Oxytocin (Correct answer)
- Estrogen
- Progesterone
Correct answer: Oxytocin
Oxytocin, released from the posterior pituitary, stimulates uterine smooth muscle contractions during labor via a positive feedback mechanism.
Question 5: Which ecological relationship benefits one organism while neither harming nor helping the other?
- Mutualism
- Parasitism
- Commensalism (Correct answer)
- Competition
Correct answer: Commensalism
Commensalism is a relationship where one organism benefits (+) while the other is unaffected (0), such as barnacles living on whale skin.
Question 6: In the cross between two heterozygous individuals (Aa × Aa), what is the expected phenotypic ratio assuming complete dominance?
- 1:2:1
- 3:1 (Correct answer)
- 1:1
- 2:1:1
Correct answer: 3:1
With complete dominance, both AA and Aa individuals express the dominant phenotype, giving a 3 dominant : 1 recessive phenotypic ratio.
Question 7: Which component of the cell membrane is responsible for its fluid mosaic structure?
- Cholesterol and phospholipids (Correct answer)
- Integral proteins only
- Carbohydrate chains
- Peripheral proteins only
Correct answer: Cholesterol and phospholipids
Phospholipid bilayers provide the fluid matrix while cholesterol modulates membrane fluidity, together creating the dynamic fluid mosaic structure.
PCAT Biology 4
Which type of epithelium lines the inner surface of blood vessels?