Free AP Biology MCQ Question and Answers — Questions and Answers
Question 1: The small intestine contains villi and microvilli, which aid in reabsorption by
- making the small intestine more hydrophobic
- increasing the surface area of the small intestine (Correct answer)
- decreasing the surface area of the small intestine
- making the small intestine more hydrophilic
Correct answer: increasing the surface area of the small intestine
Villi are finger-like projections, and microvilli are even smaller projections on the surface of the villi, creating a brush border. This extensive folding dramatically increases the internal surface area of the small intestine. A larger surface area allows for more efficient and rapid absorption of digested nutrients into the bloodstream, maximizing the uptake of essential molecules.
Question 2: In the small intestine, which of the following DOES NOT occur?
- Pepsin breaks down proteins to amino acids (Correct answer)
- Bile emulsifies fats into smaller fat particles
- Pancreatic lipase breaks down fats into fatty acids and glycerol.
- Pancreatic amylase breaks down carbohydrates into simple sugars.
Correct answer: Pepsin breaks down proteins to amino acids
Pepsin is a protease enzyme that functions optimally in the highly acidic environment of the stomach, where it begins the digestion of proteins. Once food moves into the small intestine, the pH becomes more alkaline, inactivating pepsin. Protein digestion continues in the small intestine, but it is carried out by other enzymes like trypsin and chymotrypsin, which break proteins into smaller peptides, not directly into amino acids.
Question 3: Which of the following best describes the route a secretory protein will likely take during its synthesis in an animal cell?
- Ribosome–Golgi apparatus–rough ER–secretory vesicle–plasma membrane
- Ribosome–rough ER–Golgi apparatus–secretory vesicle–plasma membrane (Correct answer)
- Plasma membrane–Golgi apparatus–ribosome–secretory vesicle–rough ER
- Plasma membrane–Golgi apparatus–ribosome–secretory vesicle–rough ER
Correct answer: Ribosome–rough ER–Golgi apparatus–secretory vesicle–plasma membrane
Secretory proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum (RER). They then enter the RER lumen for folding and modification. From the RER, they travel to the Golgi apparatus for further processing, sorting, and packaging into secretory vesicles. These vesicles then fuse with the plasma membrane, releasing the proteins outside the cell.
Question 4: The following statements about alleles are all true, EXCEPT for
- alleles are found on corresponding loci of homologous chromosomes
- an individual with two identical alleles is said to be heterozygous with respect to that gene (Correct answer)
- alleles are alternative forms of the same gene
- a gene can have more than two alleles
Correct answer: an individual with two identical alleles is said to be heterozygous with respect to that gene
An individual with two identical alleles for a particular gene is described as homozygous, not heterozygous. Heterozygous means having two different alleles for a gene. Alleles are indeed alternative forms of a gene, found at corresponding loci on homologous chromosomes, and a gene can have multiple alleles within a population.
Question 5: Which of the following statements is the LEAST plausible explanation for the seeming low frequency of mutations, despite the fact that mutations happen at a regular and predictable rate?
- Some undesirable phenotypic traits may be prevented from reproducing.
- Some mutations cause such drastic phenotypic changes that they are removed from the gene pool.
- The predictable rate of mutation results in ongoing variability in a gene pool. (Correct answer)
- Some mutations produce alleles that are recessive and may not be expressed.
Correct answer: The predictable rate of mutation results in ongoing variability in a gene pool.
While mutations do occur at a predictable rate and contribute to genetic variability, this statement doesn't explain why the *frequency* of *expressed* mutations might seem low. The other options describe mechanisms that actively reduce the observable impact or prevalence of mutations: undesirable traits are selected against, drastic changes are removed, and recessive mutations may not be expressed. The predictable rate itself doesn't explain *low frequency* in the population, but rather the *source* of new variation.
Question 6: Which of the following adaptations is least likely to be present in a creature that inhabits a hot, arid environment?
- Large ears to aid in heat dispersion
- Long loops of Henle to maximize water reabsorption
- Short loops of Henle to maximize water secretion (Correct answer)
- Storage of water in fatty tissues
Correct answer: Short loops of Henle to maximize water secretion
Animals in hot, arid environments need to conserve water to survive. Long loops of Henle are an adaptation that allows for greater reabsorption of water from the filtrate, producing highly concentrated urine and minimizing water loss. Short loops of Henle, conversely, would lead to less water reabsorption and increased water secretion, which would be detrimental in a desert environment.
Question 7: Which of the following best explains why legumes can thrive in nitrogen-deficient soils?
- These plants have a mutualistic relationship with nitrogen-fixing bacteria (Correct answer)
- These plants do not require nitrogen to make plant proteins
- These plants make their own proteins
- These plants are capable of directly converting nitrogen gas into nitrates
Correct answer: These plants have a mutualistic relationship with nitrogen-fixing bacteria
Legumes form a symbiotic relationship with nitrogen-fixing bacteria, such as Rhizobium, which reside in nodules on their roots. These bacteria convert atmospheric nitrogen gas (N2), which plants cannot directly use, into ammonia (NH3) and other nitrogen compounds that are usable by the plant. This process, called nitrogen fixation, provides the plant with essential nitrogen even in soils where it is scarce.
Free AP Biology MCQ Question and Answers
The small intestine contains villi and microvilli, which aid in reabsorption by