BIO111 Exam 4 Actual Exam V1 | BIO111 General Biology (BIO111
Exam 4) | UCLA
1. Which of the following is a necessary condition for a population to be in Hardy-Weinberg
equilibrium?
A. Natural selection must be occurring
B. Frequent mutations must occur
C. Small population size
D. Random mating must take place
Answer: D
Rationale: Hardy-Weinberg equilibrium describes a non-evolving population where allele
frequencies remain constant. One of the five essential conditions is that individuals mate
randomly without preference for specific genotypes. If mating is non-random, genotype
frequencies will deviate from the expected equilibrium values.
2. In a population of birds, individuals with medium-sized beaks survive better than those
with very small or very large beaks. This is an example of:
A. Stabilizing selection
B. Disruptive selection
C. Directional selection
D. Sexual selection
Answer: A
Rationale: Stabilizing selection favors intermediate phenotypes over extreme variations.
This process reduces genetic diversity by selecting against the outliers of a trait
distribution. It is common in environments that remain relatively stable over long periods.
3. The bottleneck effect is a form of:
A. Gene flow
B. Natural selection
C. Mutation
D. Genetic drift
Answer: D
,Rationale: The bottleneck effect occurs when a population’s size is drastically reduced by a
random environmental event. The surviving population may have allele frequencies that
differ significantly from the original population purely by chance. This leads to a loss of
genetic variation and is a classic example of genetic drift.
4. Which concept defines a species as a group of populations whose members have the
potential to interbreed and produce viable, fertile offspring?
A. Morphological species concept
B. Ecological species concept
C. Biological species concept
D. Phylogenetic species concept
Answer: C
Rationale: The biological species concept emphasizes reproductive isolation as the
primary criterion for defining species. It focuses on the ability of individuals to exchange
genes through successful reproduction. However, this concept cannot be applied to fossils
or organisms that reproduce asexually.
5. Allopatric speciation occurs when:
A. Sexual selection leads to reproductive isolation
B. Two species occupy the same geographic area
C. Polyploidy occurs within a plant population
D. A population is divided by a geographic barrier
Answer: D
Rationale: Allopatric speciation happens when a physical barrier like a mountain range or
ocean separates a population into two. Once isolated, the two groups evolve independently
through natural selection and genetic drift. Over time, they become reproductively
incompatible even if the barrier is removed.
6. Which of the following describes the ‘10% rule’ in ecological energy flow?
A. Only 10% of sun energy is captured by plants
B. Decomposers return 10% of nutrients to the soil
C. 10% of species go extinct every million years
D. Approximately 10% of energy is transferred from one trophic level to the next
Answer: D
Rationale: Energy transfer between trophic levels is highly inefficient, with most energy
lost as heat or through metabolic processes. The 10% rule estimates that only a small
, fraction of biomass is converted into new biomass at the next level. This limitation explains
why food chains rarely exceed four or five levels.
7. In the nitrogen cycle, which process converts atmospheric nitrogen (N2) into a form usable
by plants?
A. Denitrification
B. Nitrification
C. Nitrogen fixation
D. Ammonification
Answer: C
Rationale: Atmospheric nitrogen is largely inaccessible to most organisms because of its
strong triple bond. Nitrogen fixation is performed by specific bacteria that convert N2 gas
into ammonia or related compounds. This process is essential for introducing nitrogen into
the biological food web.
8. A keystone species is one that:
A. Is the most abundant species in a community
B. Is always a primary producer
C. Has a disproportionately large effect on its environment relative to its abundance
D. Has the highest biomass in the ecosystem
Answer: C
Rationale: Keystone species play a critical role in maintaining the structure and
biodiversity of an ecological community. Their removal can lead to a collapse of the
ecosystem or a significant shift in species composition. Common examples include sea
otters in kelp forests or wolves in terrestrial ecosystems.
9. What is the primary reservoir for carbon in the global carbon cycle?
A. Sedimentary rocks
B. Biomass
C. Oceans
D. Atmosphere
Answer: A
Rationale: While the atmosphere and oceans hold significant amounts of carbon, the
largest reservoir is actually found in Earth’s crust as sedimentary rocks like limestone.
Carbon is stored here for millions of years before being released through volcanic activity
Exam 4) | UCLA
1. Which of the following is a necessary condition for a population to be in Hardy-Weinberg
equilibrium?
A. Natural selection must be occurring
B. Frequent mutations must occur
C. Small population size
D. Random mating must take place
Answer: D
Rationale: Hardy-Weinberg equilibrium describes a non-evolving population where allele
frequencies remain constant. One of the five essential conditions is that individuals mate
randomly without preference for specific genotypes. If mating is non-random, genotype
frequencies will deviate from the expected equilibrium values.
2. In a population of birds, individuals with medium-sized beaks survive better than those
with very small or very large beaks. This is an example of:
A. Stabilizing selection
B. Disruptive selection
C. Directional selection
D. Sexual selection
Answer: A
Rationale: Stabilizing selection favors intermediate phenotypes over extreme variations.
This process reduces genetic diversity by selecting against the outliers of a trait
distribution. It is common in environments that remain relatively stable over long periods.
3. The bottleneck effect is a form of:
A. Gene flow
B. Natural selection
C. Mutation
D. Genetic drift
Answer: D
,Rationale: The bottleneck effect occurs when a population’s size is drastically reduced by a
random environmental event. The surviving population may have allele frequencies that
differ significantly from the original population purely by chance. This leads to a loss of
genetic variation and is a classic example of genetic drift.
4. Which concept defines a species as a group of populations whose members have the
potential to interbreed and produce viable, fertile offspring?
A. Morphological species concept
B. Ecological species concept
C. Biological species concept
D. Phylogenetic species concept
Answer: C
Rationale: The biological species concept emphasizes reproductive isolation as the
primary criterion for defining species. It focuses on the ability of individuals to exchange
genes through successful reproduction. However, this concept cannot be applied to fossils
or organisms that reproduce asexually.
5. Allopatric speciation occurs when:
A. Sexual selection leads to reproductive isolation
B. Two species occupy the same geographic area
C. Polyploidy occurs within a plant population
D. A population is divided by a geographic barrier
Answer: D
Rationale: Allopatric speciation happens when a physical barrier like a mountain range or
ocean separates a population into two. Once isolated, the two groups evolve independently
through natural selection and genetic drift. Over time, they become reproductively
incompatible even if the barrier is removed.
6. Which of the following describes the ‘10% rule’ in ecological energy flow?
A. Only 10% of sun energy is captured by plants
B. Decomposers return 10% of nutrients to the soil
C. 10% of species go extinct every million years
D. Approximately 10% of energy is transferred from one trophic level to the next
Answer: D
Rationale: Energy transfer between trophic levels is highly inefficient, with most energy
lost as heat or through metabolic processes. The 10% rule estimates that only a small
, fraction of biomass is converted into new biomass at the next level. This limitation explains
why food chains rarely exceed four or five levels.
7. In the nitrogen cycle, which process converts atmospheric nitrogen (N2) into a form usable
by plants?
A. Denitrification
B. Nitrification
C. Nitrogen fixation
D. Ammonification
Answer: C
Rationale: Atmospheric nitrogen is largely inaccessible to most organisms because of its
strong triple bond. Nitrogen fixation is performed by specific bacteria that convert N2 gas
into ammonia or related compounds. This process is essential for introducing nitrogen into
the biological food web.
8. A keystone species is one that:
A. Is the most abundant species in a community
B. Is always a primary producer
C. Has a disproportionately large effect on its environment relative to its abundance
D. Has the highest biomass in the ecosystem
Answer: C
Rationale: Keystone species play a critical role in maintaining the structure and
biodiversity of an ecological community. Their removal can lead to a collapse of the
ecosystem or a significant shift in species composition. Common examples include sea
otters in kelp forests or wolves in terrestrial ecosystems.
9. What is the primary reservoir for carbon in the global carbon cycle?
A. Sedimentary rocks
B. Biomass
C. Oceans
D. Atmosphere
Answer: A
Rationale: While the atmosphere and oceans hold significant amounts of carbon, the
largest reservoir is actually found in Earth’s crust as sedimentary rocks like limestone.
Carbon is stored here for millions of years before being released through volcanic activity
