Free AP Biology Question and Answers — Questions and Answers
Question 1: In humans, the Krebs cycle takes place in the
- outer mitochondrial membrane
- mitochondrial matrix (Correct answer)
- intermembrane space
- inner mitochondrial membrane
Correct answer: mitochondrial matrix
The Krebs cycle, also known as the citric acid cycle, is a crucial stage of cellular respiration. In eukaryotic cells, including human cells, this metabolic pathway occurs within the mitochondrial matrix, the innermost compartment of the mitochondrion. Here, acetyl-CoA is oxidized to produce ATP, NADH, and FADH2, which are essential for subsequent energy production.
Question 2: One distinction between the two types of cellular reproduction—meiosis and mitosis—is that in meiosis
- separation of sister chromatids occurs during the second division, whereas in mitosis separation of sister, chromatids occur during the first division (Correct answer)
- spindle fibers form during prophase, whereas in mitosis the spindle fibers form during metaphase
- there is one round of cell division, whereas in mitosis there are two rounds of cell division
- chromosomes are replicated during interphase, whereas in mitosis chromosomes are replicated during prophase
Correct answer: separation of sister chromatids occurs during the second division, whereas in mitosis separation of sister, chromatids occur during the first division
In mitosis, sister chromatids separate during anaphase, resulting in two identical diploid daughter cells. In contrast, meiosis involves two rounds of division. During meiosis I, homologous chromosomes separate, and then in meiosis II, sister chromatids finally separate, leading to four genetically distinct haploid daughter cells. This two-step separation is a key difference enabling genetic diversity in sexual reproduction.
Question 3: Which of the following DOES NOT describe a bacterial trait?
- Membrane-bound cellular organelles (Correct answer)
- Plasma membrane consisting of lipids and proteins
- Ribosomes that synthesize polypeptides
- Circular double-stranded DNA
Correct answer: Membrane-bound cellular organelles
Bacteria are prokaryotic organisms, meaning they lack a nucleus and other membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Their genetic material is located in a nucleoid region, and their cellular functions occur in the cytoplasm. This absence of internal compartmentalization is a defining characteristic distinguishing them from eukaryotic cells.
Question 4: Which of the following statements most accurately describes why a population is referred to as the evolutionary unit?
- Natural selection affects individuals, not populations
- Genetic changes can only occur at the population level.
- Individuals cannot evolve, but populations can (Correct answer)
- The gene pool in a population remains fixed over time
Correct answer: Individuals cannot evolve, but populations can
Evolution is defined as a change in the heritable characteristics of biological populations over successive generations. While natural selection acts on individuals, affecting their survival and reproduction, it is the population's gene pool that changes over time as advantageous traits become more common. Therefore, individuals do not evolve during their lifetime; rather, the genetic makeup of a population changes across generations.
Question 5: The endocrine system uses a variety of feedback mechanisms to maintain homeostasis. Which of the following best describes favorable criticism?
- An enzyme is allosterically inhibited by the product of the reaction it catalyzes.
- Infant suckling causes a mother's brain to release oxytocin, which in turn stimulates milk production. (Correct answer)
- When blood sugar levels decrease to normal after a meal, insulin is no longer secreted.
- When ATP is abundant the rate of glycolysis decreases
Correct answer: Infant suckling causes a mother's brain to release oxytocin, which in turn stimulates milk production.
Positive feedback mechanisms amplify an initial stimulus, pushing a physiological process further in the same direction. In the example of milk production, infant suckling stimulates the release of oxytocin, which then causes more milk to be released, leading to more suckling and further oxytocin release. This escalating cycle continues until the baby is full or the stimulus is removed.
Question 6: A guinea pig cross is performed by a scientist using two animals with identical black coats. White hair coat is subordinate to black hair coat. One-fourth of the offspring have white coats, compared to three-quarters who have black coats. Most likely, the parents' genotypes were
- Bb Ă— Bb (Correct answer)
- BB Ă— Bb
- bb Ă— bb
- Bb Ă— bb
Correct answer: Bb Ă— Bb
If black hair (B) is dominant and white hair (b) is recessive, then for 1/4 of the offspring to have white coats (bb), both parents must carry the recessive allele. A cross between two heterozygous parents (Bb x Bb) results in a genotypic ratio of 1 BB : 2 Bb : 1 bb. This translates to a phenotypic ratio of 3 black (BB, Bb) to 1 white (bb), perfectly matching the observed offspring.
Question 7: A volcanic eruption decimates a sizable island. With the exception of the group's largest male and female horses, the majority of the horses perish. They remain alive, procreate, and maintain the population. Given that weight is highly heritable and that the distribution of weights resembles a binomial distribution, the following generation's kids should have
- a lower mean weight compared with their parents
- a higher mean weight compared with members of the original population (Correct answer)
- a higher mean weight compared with their parents
- the same mean weight as members of the original population
Correct answer: a higher mean weight compared with members of the original population
This scenario describes a bottleneck effect, a type of genetic drift where a population undergoes a drastic reduction in size. Since only the largest male and female horses survived, they represent a non-random sample of the original population's gene pool. Because weight is highly heritable, their offspring will inherit genes predisposing them to larger size, thus increasing the average weight of the new population compared to the original diverse population.
Free AP Biology Question and Answers
In humans, the Krebs cycle takes place in the