Question
Acacia ants (Pseudomyrmex ferruginea) live on acacia trees (Vachellia cornigera). The ants obtain food and shelter from the acacia trees, and
the ants drive away animals that would otherwise eat the leaves of the acacia trees.
Which of the following best describes the relationship between Pseudomyrmex ferruginea and Vachellia cornigera?
(A) niche partitioning
(B) commensalism
(C) mutualism
(D) parasitism
▶️Answer/Explanation
Ans:
(C) Since both the ants and the acacia trees benefit from the
relationship, the symbiosis between them is mutualistic. Niche
partitioning is using different parts of a resource, so choice (A) is
incorrect. Choice (B) is incorrect because commensalism benefits one
member of the symbiosis but the other member neither benefits nor is
harmed. In parasitism, one member of the symbiosis benefits but the
other is harmed, so choice (D) is incorrect.
Question
Two species of lynx spiders, Peucetia rubrolineata and Peucetia flava, both inhabit the plant Trichogoniopsis adenantha, a type of sunflower found in Brazil. However, Peucetia rubrolineata inhabit plants in shaded areas, while Peucetia flava inhabit plants in open areas. This is
an example of
(A) competition.
(B) mutualism.
(C) niche partitioning.
(D) predator/prey relationship.
▶️Answer/Explanation
Ans:
(C) Niche partitioning occurs when different species use a limited
resource differently. The two species of spiders use the same species of
plant, but one species of spiders only uses plants in the shade while the
other only uses plants in open areas. So they partition the resource
differently. Choice (A) is incorrect because the spiders are not in direct
competition for the same resource. This is not a mutualistic relationship
between the spiders because they do not provide a benefit to each other,
so choice (B) is incorrect. Choice (D) is incorrect because the spiders
do not prey on each other.
Question
Cytisus scoparius, also known as Scotch broom, was introduced into California from England in the mid-1800s as an easy-to-grow plant that helped stabilize soil on the hillsides. One Scotch broom plant can produce over 12,000 seeds a year. Scotch broom forms a dense shade
canopy that prevents seedlings of other plants from growing. There are no natural predators for Scotch broom in California since its leaves are toxic to most animal species.
Which of the following most accurately describes Scotch broom’s role in the California ecosystem?
(A) keystone species
(B) invasive species
(C) mutualistic species
(D) native species
▶️Answer/Explanation
Ans:
(B) Scotch broom is not native to California. It outcompetes other
plants and has no natural predators in California, so it is an invasive
species. Choice (A) is incorrect because if a keystone species is
removed, the entire ecosystem may collapse. Removing Scotch broom
would most likely help the ecosystem, not cause it to collapse. Scotch
broom does not benefit other organisms in this ecosystem; therefore, it
is not a mutualistic species and choice (C) is incorrect. Choice (D) is
incorrect because Scotch broom is not native to California.
Question
Refer to the following graph of shell thickness in two populations of blue mussels (Mytilus edulis). Northern populations of
mussels live among the Carcinus crab, while southern populations live among both Carcinus and Hemigrapsus crabs.
Young mussels that had never experienced interactions with crabs were taken from northern and southern populations and grown under one of three different controlled conditions. The mussels were exposed either to no crabs or to Carcinus or Hemigrapsus crabs in cages nearby. The crabs were kept in cages for the duration of the experiment and could not eat the mussels.
Which of the following statements accurately compares the response to crab exposure by the northern and southern mussel populations?
(A) The mussels exposed to Carcinus crabs have thicker shells than
the mussels exposed to Hemigrapsus crabs in the northern
population, but the mussels exposed to Hemigrapsus crabs have
a thicker shell than the mussels exposed to Carcinus crabs in the
southern population.
(B) The northern population experienced greater increases in shell
thickness overall relative to the southern population.
(C) The southern population had greater increases in shell thickness
because they had thinner shells at the start of the experiment.
(D) Increases in shell thickness were greatest in response to the
crabs that the mussels’ original populations had exposure to.
▶️Answer/Explanation
Ans: D
The mussel shell thickness was measured in the experiment (so
choice A is incorrect). The mussels that were bred from the original northern
population of mussels had no previous exposure to Carcinus, yet their shells
thickened the most when exposed to Carcinus.
The mussels bred from the southern population of mussels also showed
increased shell thickness with exposure to Carcinus and Hemigrapsus even
though those specific mussels had never been exposed to either type of crab.
Question
Refer to the following graph of shell thickness in two populations of blue mussels (Mytilus edulis). Northern populations of
mussels live among the Carcinus crab, while southern populations live among both Carcinus and Hemigrapsus crabs.
Young mussels that had never experienced interactions with crabs were taken from northern and southern populations and grown under one of three different controlled conditions. The mussels were exposed either to no crabs or to Carcinus or Hemigrapsus crabs in cages nearby. The crabs were kept in cages for the duration of the experiment and could not eat the mussels.
Which of the following statements is a biologically correct inference from the data?
(A) Interactions between individuals can result in evolution.
(B) Traits learned or acquired by parents can be transmitted to
offspring.
(C) Mussels secrete chemicals that increase the thickness of shells
of nearby mussels.
(D) Mussels can change their shell thickness in response to fear.
▶️Answer/Explanation
Ans: A
The mussels in the experiment were naïve to crabs; in other words,
they were never exposed to crabs. The fact that the shell thickness
increased only when exposed to the type of crab the native population of
the mussels had been exposed to indicates that the population from
which they were derived had adapted to the presence of the specific crab.
This requires the ability to detect the presence of the specific type of crab that
was a threat and effect a response (thicken their shell).
However, the increase in shell thickness was technically an
acclimation, made possible by the adaptation of the ability to sense and
respond to the presence of specific crabs that the mussels were never
exposed to.
Choice B is incorrect because the ability to respond to the presence of a
specific crab was an adaptation, not the inheritance of a learned or acquired
trait. Choice C is incorrect because there is no indication of the mechanism of
shell thickening. It is likely that the mussels can chemically detect the
presence of the crabs, but there is nothing to indicate that mussels must be
near other mussels to have the response. Choice D is incorrect because there
is no indication that mussels feel fear, although they can clearly perceive
certain threats.