General Biology Flashcards

In an experiment, a gene is expressed in muscle tissue but silenced in nerve tissue. This best illustrates:

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.

Which component of the immune system produces antibodies?

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.

The primary function of the loop of Henle in the kidney is to:

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.

Which of the following best describes a sympatric speciation event?

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.

Which nitrogenous base is found in RNA but NOT in DNA?

Answer: Uracil

RNA contains uracil (U) instead of thymine (T), and uracil pairs with adenine just as thymine does in DNA.

A student observes that a bacterial colony grows on a plate containing ampicillin. This resistance is most likely due to:

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.

During the Calvin cycle, CO₂ is first incorporated into a stable organic molecule by combining with:

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.