Question
Triclosan is an antibacterial chemical that is used in some household products to reduce bacteria levels. Which of the following is the most
likely result of increased use of products that contain triclosan over time?
(A) All household bacteria species will be eliminated.
(B) Household bacteria species will become resistant to triclosan.
(C) Individual bacteria will learn how to resist the effects of triclosan.
(D) Increased triclosan levels will increase the frequency of mutations
in household bacteria.
▶️Answer/Explanation
Ans:
(B) Increased use of products that contain triclosan will create an
environment in which triclosan-resistant bacteria have a survival
advantage, so over time the relative numbers of triclosan-resistant
bacteria will increase. Choice (A) is incorrect because there is no
evidence that triclosan kills all bacteria. Individuals do not evolve,
populations evolve, so choice (C) is incorrect. Choice (D) is incorrect
because there is no evidence in the question that the use of triclosan
increases the frequency of mutations in bacteria.
Question
Refer to the data below showing the evolution of drug resistance in Moraxella catarrhalis, a bacteria that causes middle ear infections in children. (Data adapted from Levin and Anderson, 1999.)
Which of the following statements is an accurate conclusion based on the data and modern evolutionary theory?
(A) As the number of resistant strains increases, a greater volume of
antibiotics is required to kill them.
(B) An increase in the prevalence of resistant bacteria directly caused
an increase in the use of antibiotics.
(C) Lowering the volume of antibiotic use would result in a decreased
prevalence of resistant strains.
(D) It is highly probable that increased use of antibiotics directly
caused an increase in the prevalence of resistant bacterial strains.
▶️Answer/Explanation
Ans: D
A graph like this is suggestive of a cause-and-effect relationship
but is not proof. There are two things compared over time. Importantly, the
two y-variables, for the most part, increase and decrease concurrently (with
a reasonable time lag between changes in drug use and changes in
prevalence of resistant bacteria as the bacteria need time to adapt). For
example, the increased drug volume from 1986–1990 correlates with an
increase in the prevalence of resistant bacteria. However, the reduction of
drug volume in 1985 and 1991 is accompanied by a decrease in the
prevalence of resistant bacteria.
Although the relationship is not perfectly correlated (e.g., in the year
1984, a decreased drug volume corresponded to very little change in
resistance), the general trend shows that as drug volume increased, the
prevalence of resistant strains increased with some lag time, and when drug
volume decreased, the prevalence of resistant strains decreased. This graph
alone allows us to say nothing of a causal relationship between the two factors but knowledge of evolutionary theory and antibiotic
Question
Which of the following statements most accurately describes the trend in plant evolution indicated in the table above?
(A) Plants evolved mechanisms for inhabiting many terrestrial
habitats by evolving mechanisms of water transport and
reproduction that do not require water.
(B) Plants were only able to survive on land once they evolved
vascular tissue.
(C) Pollen and seeds evolved so that plants could live on land without
drying out.
(D) Flowers and fruits evolved so plants could store energy on land
without having to rely on seeds.
▶️Answer/Explanation
Ans: A
One of the biggest problems facing terrestrial organisms is the
possibility of desiccation (drying out). Plants have the added challenge of
being sessile (they don’t move). Plant evolution began on land, and only
after they were established in a terrestrial environment did some species
begin to inhabit aquatic environments. (Remember that seaweed, kelp, and
algae are not plants!)
Choice B is incorrect because mosses are plants and they live on land
without vascular tissue (though their size is limited, as is their range—they
must live near water to reproduce). Choice C is incorrect because pollen
and seeds are not needed to survive on land, but they do allow plants to
reproduce in the absence of water (swimming sperm make mosses and
ferns dependent on water for reproduction), an adaptation needed to
disperse into a greater diversity of territories. Choice D is incorrect because
flowers are reproductive organs and fruits are seed dispersal structures.
Both structures allow angiosperms to reproduce in the absence of water, but
they do not provide energy to the plant that grew them. Fruits and flowers require energy to grow! The stored food in the seed provides energy to
the plant embryo. The fruit helps disperse the seed, often by giving
animals something to eat.
A fruit, by definition, is a structure that aids in seed dispersal. Not all
fruits are for eating! Many fruits are structures that allow seeds to get away
from their parents by wind (the fruit is winged, like samaras), by water (the
fruit is buoyant), or by sticking to animal fur (the fruit has hooks or burrs).
Question
One aspect of the lifestyle of plants gives rise to a whole suite of related challenges. Which aspect of plant life is the root cause of the other challenges listed here?
(A) avoiding predation (herbivory)
(B) choice of location
(C) mate choice
(D) sessile existence
▶️Answer/Explanation
Ans: D
Because plants are sessile (they can’t move), choices A, B, and C
are all problems the plant faces.
Question
Insects first evolved approximately 479 million years ago. The first flying insects evolved around 406 million years ago. Birds evolved from therapod dinosaurs approximately 160 million years ago. The functional similarity between the wings of a bird and the wings of an insect is:
(A) the result of divergent evolution.
(B) an example of analogous structures.
(C) the result of the convergent evolution of two common ancestors.
(D) the direct result of adaptive radiation.
▶️Answer/Explanation
Ans: B
Flight evolved in invertebrate insects (a class of arthropods) 406
million years ago and evolved completely independently in the vertebrates
160 million years ago. The common ancestor between the birds and the
insects did not have wings. (Flight also evolved independently in the
mammals!)
The structure of bird wings and insect wings are completely different.
They share a similar function, flying, because the ability to fly was an
advantage to both organisms. Because the common ancestor of the birds
and the insects did not have wings (or wing-like structures), wings must
have evolved independently in the two groups (as indicated by their
completely different morphology as well as the evolutionary history). This
is an example of convergent evolution, which occurs when two different
species adapt to their environments in similar ways (e.g., they evolve
wings), but they do not become more genetically similar and do not have a
recent common ancestor that possessed the trait in question.
- Convergent evolution produces analogous structures. How are
you supposed to know that the common ancestor of birds and insects
didn’t have wings? Birds are chordates (and vertebrates), and insects
are arthropods (invertebrates). You only have to trace the bird
lineage back to its fish ancestors to know the common ancestor
(which was hundreds of millions of years before the fish) didn’t
have wings. As far as the other answers are concerned, homology is the result of divergent evolution, so choices B and C are incorrect.
(See the table after answer 20.) - Divergent evolution produces homologous structures.
Of course we’re all related to the universal common ancestor, a
prokaryote that inhabited Earth 3.8 billion years ago, but multiple
divergences allowed different populations to take different evolutionary
paths to the present day.