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 favoured.
C. Medium-sized clutches are less frequent.
D. Smaller and larger clutches are rarely found.
▶️Answer/Explanation
Ans. D
Given that clutch size in American robins is influenced by stabilizing selection, it can be inferred that the distribution of clutch sizes in the population is likely to follow a bell curve. Most robins will have a clutch size near the optimal number for successful hatching, with fewer individuals having either very small or very large clutches. Stabilizing selection favors the middle range of clutch sizes because they are associated with higher reproductive success, leading to a concentration of individuals with moderate clutch sizes.
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
Ans:D
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
Markscheme
D
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
Markscheme
B
Question
The graph shows variations in beak size for the bird Geospiza fortis on an island in the Galápagos archipelago.
What evidence from the graph indicates that disruptive selection is occurring?
A. An intermediate beak size is less common.
B. Median beak size is the most common.
C. Smaller beaks are favoured.
D. Larger beaks are favoured.
▶️Answer/Explanation
Ans:A