GACE Biology 2 — Questions and Answers
Question 1: Which organelle is primarily responsible for ATP synthesis through oxidative phosphorylation in eukaryotic cells?
- Ribosome
- Mitochondria (Correct answer)
- Endoplasmic reticulum
- Golgi apparatus
Correct answer: Mitochondria
Mitochondria carry out oxidative phosphorylation via the electron transport chain and ATP synthase to produce the majority of cellular ATP.
Question 2: A student observes that a population of beetles in a field has shifted from mostly green to mostly brown over 20 generations. Which mechanism best explains this change if brown beetles survive predation better?
- Genetic drift
- Natural selection (Correct answer)
- Gene flow
- Mutation pressure
Correct answer: Natural selection
Natural selection favors traits that increase survival and reproduction, so brown coloration providing better camouflage increases in frequency over generations.
Question 3: Which bond type links nucleotides together to form the backbone of a DNA strand?
- Hydrogen bonds
- Ionic bonds
- Phosphodiester bonds (Correct answer)
- Peptide bonds
Correct answer: Phosphodiester bonds
Phosphodiester bonds connect the 3' hydroxyl of one nucleotide to the 5' phosphate of the next, forming the sugar-phosphate backbone.
Question 4: During meiosis I, homologous chromosomes exchange genetic material through a process called:
- Synapsis
- Crossing over (Correct answer)
- Independent assortment
- Disjunction
Correct answer: Crossing over
Crossing over (recombination) occurs at chiasmata during prophase I, exchanging segments between non-sister chromatids of homologous chromosomes.
Question 5: An ecosystem experiences the removal of all top predators. According to trophic cascade theory, what is the most likely outcome?
- Primary producer biomass decreases
- Herbivore populations decrease
- Herbivore populations increase and primary producer biomass decreases (Correct answer)
- Decomposer activity increases immediately
Correct answer: Herbivore populations increase and primary producer biomass decreases
Without top predators to control herbivore populations, herbivores increase and overconsume primary producers, reducing their biomass.
Question 6: Which term describes the movement of water across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration?
- Active transport
- Facilitated diffusion
- Osmosis (Correct answer)
- Endocytosis
Correct answer: Osmosis
Osmosis is the passive movement of water across a selectively permeable membrane down its own concentration gradient (from lower to higher solute concentration).
Question 7: A mutation that changes a codon from UAU (tyrosine) to UAA (stop) is classified as a:
- Missense mutation
- Silent mutation
- Nonsense mutation (Correct answer)
- Frameshift mutation
Correct answer: Nonsense mutation
A nonsense mutation converts an amino-acid-coding codon into a premature stop codon, truncating the resulting protein.
GACE Biology 2
Which organelle is primarily responsible for ATP synthesis through oxidative phosphorylation in eukaryotic cells?