OAT General Biology 4 — Questions and Answers
Question 1: In an experiment, a gene is expressed in muscle tissue but silenced in nerve tissue. This best illustrates:
- Gene mutation
- Differential gene expression (Correct answer)
- Chromosomal deletion
- RNA splicing error
Correct answer: Differential gene expression
Differential gene expression occurs when the same genome produces different proteins in different cell types based on which genes are active.
Question 2: Which component of the immune system produces antibodies?
- T cytotoxic cells
- Natural killer cells
- B plasma cells (Correct answer)
- Neutrophils
Correct answer: B plasma cells
B cells differentiate into plasma cells upon antigen activation, and plasma cells are the antibody-secreting effector cells of humoral immunity.
Question 3: The primary function of the loop of Henle in the kidney is to:
- Filter blood under pressure
- Reabsorb glucose
- Create a concentration gradient in the medulla (Correct answer)
- Secrete hydrogen ions
Correct answer: Create a concentration gradient in the medulla
The loop of Henle establishes a hyperosmotic gradient in the renal medulla through countercurrent multiplication, which drives water reabsorption from the collecting duct.
Question 4: Which of the following best describes a sympatric speciation event?
- A mountain range geographically separates a population
- New species arise within the same geographic area (Correct answer)
- Plate tectonics isolates island populations
- A river divides a single species into two groups
Correct answer: New species arise within the same geographic area
Sympatric speciation occurs without geographic isolation, often through polyploidy, sexual selection, or ecological divergence within the same habitat.
Question 5: Which nitrogenous base is found in RNA but NOT in DNA?
- Adenine
- Cytosine
- Uracil (Correct answer)
- Guanine
Correct answer: Uracil
RNA contains uracil (U) instead of thymine (T), and uracil pairs with adenine just as thymine does in DNA.
Question 6: A student observes that a bacterial colony grows on a plate containing ampicillin. This resistance is most likely due to:
- Phenotypic plasticity
- Acquired mutation providing selective advantage (Correct answer)
- Lamarckian inheritance
- Induced immunity
Correct answer: Acquired mutation providing selective advantage
Pre-existing random mutations that confer antibiotic resistance are selected for in the presence of the antibiotic, illustrating natural selection at the microbial level.
Question 7: During the Calvin cycle, CO₂ is first incorporated into a stable organic molecule by combining with:
- Glucose-6-phosphate
- Pyruvate
- Ribulose-1,5-bisphosphate (RuBP) (Correct answer)
- Oxaloacetate
Correct answer: Ribulose-1,5-bisphosphate (RuBP)
The enzyme RuBisCO catalyzes the fixation of CO₂ onto RuBP (a 5-carbon acceptor), producing two 3-carbon molecules of 3-phosphoglycerate.
OAT General Biology 4
In an experiment, a gene is expressed in muscle tissue but silenced in nerve tissue.
This best illustrates: