IB Biology 2 — Questions and Answers
Question 1: Which enzyme is responsible for unwinding the DNA double helix during replication?
- DNA polymerase III
- Helicase (Correct answer)
- Ligase
- Primase
Correct answer: Helicase
Helicase breaks the hydrogen bonds between complementary bases to unwind and separate the two strands of the double helix.
Question 2: What is the role of the rough endoplasmic reticulum (rER) in protein secretion?
- Packaging proteins into vesicles for export
- Synthesizing proteins on attached ribosomes (Correct answer)
- Modifying proteins with carbohydrate chains
- Sorting proteins to their final destinations
Correct answer: Synthesizing proteins on attached ribosomes
The rough ER bears ribosomes on its surface where secretory proteins are synthesized and threaded into the ER lumen.
Question 3: In which stage of meiosis do homologous chromosomes separate?
- Meiosis I anaphase (Correct answer)
- Meiosis II anaphase
- Meiosis I metaphase
- Meiosis II metaphase
Correct answer: Meiosis I anaphase
During anaphase I, spindle fibers pull homologous chromosome pairs to opposite poles, reducing the chromosome number by half.
Question 4: Which type of selection leads to two distinct phenotypic peaks in a population?
- Directional selection
- Stabilizing selection
- Disruptive selection (Correct answer)
- Artificial selection
Correct answer: Disruptive selection
Disruptive selection favors extreme phenotypes at both ends of the distribution, often splitting a population into two distinct groups.
Question 5: What is the primary reason temperature affects enzyme activity?
- Temperature changes the substrate concentration
- High temperatures denature the enzyme's active site (Correct answer)
- Low temperatures increase substrate collision frequency
- Temperature alters the enzyme's molecular weight
Correct answer: High temperatures denature the enzyme's active site
Excessive heat breaks the bonds maintaining the tertiary structure of the enzyme, distorting the active site so substrate can no longer bind effectively.
Question 6: Which photosynthetic pigment absorbs red and blue light most effectively while reflecting green light?
- Carotenoids
- Xanthophylls
- Chlorophyll a (Correct answer)
- Phycobilins
Correct answer: Chlorophyll a
Chlorophyll a, the primary photosynthetic pigment, strongly absorbs red (~680 nm) and blue (~430 nm) wavelengths and reflects green, giving leaves their color.
Question 7: How does the sodium-potassium pump contribute to the resting membrane potential of a neuron?
- It moves 3 Na⁺ out and 2 K⁺ in, creating a net negative interior (Correct answer)
- It moves 2 Na⁺ out and 3 K⁺ in, creating a net positive interior
- It opens ligand-gated channels to depolarize the membrane
- It equalizes ion concentrations on both sides of the membrane
Correct answer: It moves 3 Na⁺ out and 2 K⁺ in, creating a net negative interior
The pump actively transports 3 sodium ions out and 2 potassium ions in per cycle, maintaining a net negative charge inside the neuron.
IB Biology 2
Which enzyme is responsible for unwinding the DNA double helix during replication?