Question
▶️Answer/Explanation
A cladogram is a branching diagram that shows the evolutionary relationships between different species. The closer two species are on the diagram, the more recently they shared a common ancestor.
Evaluation of Each Option:
A. Incorrect – Baboons do share a common ancestor with gorillas, humans, and chimpanzees, though the split occurred earlier. All species on a cladogram ultimately trace back to a common ancestor.
B. Correct – Humans and chimpanzees appear closest together on the cladogram, meaning they share the most recent common ancestor compared to gorillas and baboons.
C. Incorrect – The baboon is one of the species on the cladogram, not the common ancestor. The common ancestor is represented by the node from which all four species branch.
D. Incorrect – Evolutionary splits shown on a cladogram do not represent equal time intervals unless explicitly stated (which is rare). Branch length doesn’t necessarily mean equal timing.
Question
A central idea in the theory of evolution is that species may evolve gradually over time from a common ancestor.
I. Beak shape shows genetic variability in the common ancestor.
II. Changes in beak shape that occur during the lifetime of an individual bird are passed on to the next generation.
III. Changes in beak shape are heritable and make each species better adapted to its environment.
▶️Answer/Explanation
How does evolution explain the development of different traits (like beak shape)?
Evolution by natural selection involves heritable genetic variation. Individuals with traits better suited to their environment are more likely to survive and reproduce, passing those traits to the next generation. Importantly, acquired traits (like changes that happen during an organism’s lifetime) are not inherited.
Evaluation of Statements:
I. Correct – Genetic variation in the beak shape would have existed in the original population (common ancestor). Natural selection acts on this variation.
II. Incorrect – This reflects the outdated Lamarckian idea that traits acquired during an individual’s life (like muscles or beak wear) are inherited. Modern biology shows that only genetic traits are passed on.
III. Correct – Changes in beak shape are due to genetic differences. If these differences help a bird survive and reproduce, they are passed on, making the population better adapted over time.
Question
Clutch size refers to the number of eggs laid by a female bird in a single breeding attempt. In American robins (Turdus migratorius), clutch size varies within the population. It is a phenotypic trait that is linked to the number of successful hatches and is subject to stabilizing selection.
What can be inferred about the distribution of clutch sizes in American robin populations?
A. Only larger clutches are common.
B. Only smaller clutches are favored.
C. Medium-sized clutches are less frequent.
D. Smaller and larger clutches are rarely found.
▶️Answer/Explanation
Answer: D. Smaller and larger clutches are rarely found.
Explanation:
What is stabilizing selection?
Stabilizing selection is a type of natural selection where individuals with average or intermediate traits are favored over those with extreme traits. This reduces variation in the population and maintains the status quo. In this case, clutch size (number of eggs laid) is under stabilizing selection.
Inference from Stabilizing Selection on Clutch Size:
- If medium-sized clutches lead to more successful hatches, birds with very small or very large clutches are less likely to pass on their genes.
- Therefore, extreme clutch sizes (small or large) become less frequent in the population.
Evaluation of Options:
A. Incorrect – If only large clutches were common, that would suggest directional selection, not stabilizing.
B. Incorrect – This would also imply directional selection toward small clutches, which is not the case here.
C. Incorrect – Medium-sized clutches are actually the most frequent under stabilizing selection, not less frequent.
D. Correct – This describes stabilizing selection correctly: both smaller and larger clutches are rare, and medium-sized clutches are most common.
Question
Which of the adaptations of flowers would be most successful for the survival of a species?
A. Spiny seeds for better wind dispersal
B. Different flowering times for better seed dispersal
C. Sticky pollen for better water dispersal
D. Specific odours for better insect pollination
▶️Answer/Explanation
Answer: D. Specific odours for better insect pollination
Explanation:
Flowering plants have evolved specific adaptations to enhance pollination and seed dispersal, which increases their chances of reproducing and spreading successfully. The most successful adaptations improve pollination by animals or wind, or seed dispersal by wind, water, or animals.
Evaluation of Options:
A. Incorrect – Spiny seeds are typically adapted for animal dispersal, not wind. Wind-dispersed seeds are usually light and winged, not spiny.
B. Incorrect – Different flowering times help reduce competition, but they don’t directly improve seed dispersal. Also, spreading out flowering too much could reduce pollination success.
C. Incorrect – Sticky pollen is not adapted for water dispersal. In fact, water pollination is rare. Sticky pollen is typically adapted for animal (especially insect) pollination.
D. Correct – Specific odours are an effective adaptation to attract pollinators like bees, flies, or moths. This increases the chance of successful pollination, which is essential for producing seeds and ensuring species survival.
What is the mechanism of natural selection?
A. Any individuals in a population can be selected entirely by chance.
B. After a change in the environment a species will evolve adaptations to the new conditions.
C. If an adaptation to the environment is useful, an individual will develop it and pass it on to its offspring.
D. Variations amongst individuals of a population are selected by a changing environment.
Answer/Explanation
Answer: D. Variations amongst individuals of a population are selected by a changing environment.
Explanation:
Natural selection is the process where individuals with traits that are better suited to their environment are more likely to survive and reproduce, passing on these beneficial traits to the next generation. Over time, these advantageous traits become more common in the population.
Let’s evaluate the options:
A. Incorrect – Natural selection is not a matter of chance. While mutations occur randomly, the selection of beneficial traits is not random but influenced by how well they help individuals survive and reproduce in their environment.
B. Incorrect – While natural selection can lead to adaptations in response to environmental changes, this is a gradual process over generations. A species does not evolve adaptations immediately after an environmental change natural selection works overtime.
C. Incorrect – Individuals do not develop traits during their lifetime in response to environmental pressures (this is Lamarckian inheritance, not Darwinian natural selection). Traits that are beneficial must already be present in the population and are passed on if they increase reproductive success.
D. Correct – Variations in traits exist among individuals in a population. The environment “selects” individuals with traits that give them a survival or reproductive advantage, which then become more common in the population over generations.
A bacterial population with no resistance to an antibiotic may develop into a bacterial population with some resistance to an antibiotic. Which event could lead to this?
A. Antibiotic resistance was inherited from an ancestral population.
B. An antibiotic resistance plasmid is received from a bacterium in another population.
C. The enzyme needed for antibiotic resistance is received from a bacterium in another population.
D. The bacterial population mutated in response to antibiotics in the environment.
Answer/Explanation
Answer: B. An antibiotic resistance plasmid is received from a bacterium in another population.
Explanation:
A. Antibiotic resistance was inherited from an ancestral population.
Incorrect – If the population originally had no resistance, it would not have inherited resistance from its ancestors. Resistance could develop over time through mutations or horizontal gene transfer, but not as an inherited trait from an initial non-resistant population.
B. An antibiotic resistance plasmid is received from a bacterium in another population.
Correct – Bacteria can acquire resistance through horizontal gene transfer. This typically happens through processes like conjugation, where a bacterium receives a plasmid (a small DNA molecule) that contains resistance genes from another bacterium. This is one of the most common ways antibiotic resistance spreads among bacteria.
C. The enzyme needed for antibiotic resistance is received from a bacterium in another population.
Incorrect – This is a bit unclear because “enzymes” are typically proteins that can be coded for by genes, which can be transferred via plasmids or other genetic mechanisms. The enzyme itself wouldn’t be “received” directly; rather, the genes encoding the enzyme could be transferred.
D. The bacterial population mutated in response to antibiotics in the environment.
Incorrect – Mutations happen randomly and aren’t caused by the presence of antibiotics. However, in the presence of antibiotics, bacteria with beneficial mutations (like antibiotic resistance) will survive and reproduce. This is the process of natural selection, not the mutation itself occurring as a direct response to antibiotics.