OAT Biology 3 — Questions and Answers
Question 1: Which layer of the skin contains melanocytes?
- Stratum corneum
- Stratum granulosum
- Stratum basale (Correct answer)
- Stratum spinosum
Correct answer: Stratum basale
Melanocytes reside in the stratum basale (deepest epidermal layer) and produce melanin pigment.
Question 2: The Calvin cycle (light-independent reactions) occurs in which part of the chloroplast?
- Thylakoid membrane
- Outer membrane
- Stroma (Correct answer)
- Intermembrane space
Correct answer: Stroma
Carbon fixation via the Calvin cycle takes place in the stroma, where RuBisCO converts CO₂ into G3P.
Question 3: Which immunoglobulin class is the FIRST to be produced in a primary immune response?
- IgG
- IgA
- IgE
- IgM (Correct answer)
Correct answer: IgM
IgM is the first antibody produced during a primary immune response before class switching occurs.
Question 4: The enzyme that unwinds the double helix ahead of the replication fork is called:
- DNA polymerase III
- Primase
- Helicase (Correct answer)
- Ligase
Correct answer: Helicase
Helicase breaks hydrogen bonds between base pairs to unwind the DNA double helix at the replication fork.
Question 5: Which of the following is an example of negative feedback in the endocrine system?
- Oxytocin release during childbirth
- Progesterone inhibiting FSH and LH secretion (Correct answer)
- LH surge triggering ovulation
- Epinephrine amplifying its own release
Correct answer: Progesterone inhibiting FSH and LH secretion
Progesterone's inhibition of FSH and LH is classic negative feedback, dampening the hormone signal that caused its release.
Question 6: In a dihybrid cross between two AaBb individuals, what fraction of offspring are expected to be aabb?
- 1/4
- 1/8
- 1/16 (Correct answer)
- 3/16
Correct answer: 1/16
Each locus independently has a 1/4 chance of yielding the homozygous recessive; combined probability = 1/4 × 1/4 = 1/16.
Question 7: Which type of muscle tissue is involuntary and striated?
- Skeletal muscle
- Smooth muscle
- Cardiac muscle (Correct answer)
- Both skeletal and cardiac
Correct answer: Cardiac muscle
Cardiac muscle is involuntary (autonomically controlled) and striated due to organized sarcomere structure.
OAT Biology 3
Which layer of the skin contains melanocytes?