Download Biology 4974/5974

Biology 4974/5974
D. F. Tomback
Name KEY
Student ID number
Fall 2013
100 points
Evolution
Exam #1: Take Home Exam
Read this before taking the exam. Please word-process your answers. You are free to
use class notes, papers posted on Canvas, and information in your textbook in order to
answer questions. A few things to warn you about:
 I expect that answers will be written in complete, well-constructed sentences, with
names and terminology spelled correctly. Misspellings and writing problems will
result in deducted points.
 Make sure that you understand what the question is asking before writing an
answer.
 Be very careful to use your own wording for answers. Students consciously or
unconsciously may plagiarize when using source materials. Plagiarism violates
the UCD honor code and public ethics and will result in an F on this assignment.
 You can take as much space as you need for your answers. (More is not always
better if you are on the wrong track.)
1. (6 pts) Evolution is regarded as a theory in science.
a. What is a theory? In science, a theory is an explanation of cause and
effect that that has supported by repeated observation or experimentation and an
accumulating wealth of evidence. (3 pts)
b. Explain the significance of the fact that evolution is a theory: what does that
mean regarding this field of study? Evolution as a theory means that its basic
tenets, such as descent with modification and the mechanism of natural selection
have been supported by a body of scientific observation and experimentation. (3
pts)
2. (4 pts) a. Does the study of evolution follow the scientific method? Yes, the study
of evolution follows the scientific method, which is based on hypothesis testing.
(2 pts)
b. What are at least two different approaches (sources of information) used by
scientists who study evolution? (2 pts each)
i. Scientists may construct hypotheses concerning the fossil record.
Ii Scientists may use a comparative approach, studying organisms
and their relationships. The mechanisms of evolution and adaptation,
inheritance, and genetic diversity may be studied experimentally as well.
3. (4 pts) What is being defined below?
a. “Unites individuals that share more characteristics (features) with one another
than they do with any other organism.” Morphological Species Concept
b. “Two species bearing the same phenotype caused by common ancestry for
the same genotype.” Homology
2
4. (10 pts) What contribution did each of the following individuals make to the
development of our understanding of biological species? (2 pts each unless noted)
a. George Buffon –Believed that species were biological units, and that species
were reproductively isolated from one another.
b. Carl von Linné (Linnaeus) –Provided a basis for describing species, the binomial
system, by noting the most important features. He also initiated a hierarchical
classification system, reflecting degrees of relationships. He also noted the
existence of races or varieties within a species, which acknowledges variation.
c. Jean-Baptiste de Lamarck—Believed that species change over time. Provided
the first biologically-based explanation for gradual change in species over time,
although it was later discredited.
d. Charles Darwin and Alfred Russel Wallace—Together recognized the mechanism
of natural selection and presented it to the Linnaean Society. (4 pts)
5. (6 pts) Present a summary of how natural selection works, listing the step by step
processes involved.
 Most species have high reproductive rates.
 Finite food and space limits numbers of individuals.
 Also, predation, parasitism, disease, competition, climate further weed out
the susceptible or weak.
 Individuals vary in characteristics.
 Certain variation results in higher survival and/or better reproduction.
 Thus, relatively greater contribution of offspring from some individuals.
 Their offspring may in turn have similar traits because of inheritance.
 Thus, certain “favored” variation spreads through the species over time.
 Leads to “descent with modification” or evolution over time.
6. (6 pts) Mayr, in his essay, “Darwin’s influence on modern thought,” brought up many
good ideas. Pick two of the following and explain their meaning: “population thinking”,
“historicity” in science, “Darwin does away with determinism”, or “theory of common
descent.”
Population thinking: Involves a rejection of ‘typology’, which means the all
members of a species are expected to follow an identical type as believed by
Aristotle. But, populations consist of unique individuals who vary from each
other.
Historicity: Reconstruction of what led to past events. Proposed scenario is
tested with information as it becomes available.
Determinism: Darwin recognized that chance played a role in evolution in terms
of the variation within species, but that natural selection sorts this out. This view
contrasted with previous views of predictability in natural processes.
Theory of common descent: Humans are descended from the same common
ancestor as all organisms. Anatomical comparisons indicate the connection with
living primates. Thus, man is not the product of special creation.
3
7. (10pts) Explain Darwin’s literary strategy or approach for the first four chapters of
On the Origin of Species.
a. Why did he begin with Chapter I, Variation under Domestication?
First of all, the British public could relate to the breeding of domesticated animals
and plants. (1 pt) They could understand Darwin’s discussion about the “power of
selective breeding” leading to exaggerating desired traits in plants and animals.(2
pts). Secondly, this was a good way to communicate the existence of individual
variation, both in physical traits but also in animal disposition, in a way the public
could understand.
b. Why did he then transition to Chapter II, Variation under Nature?
He then pointed out that variation was well documented in natural species, and
there was so much individual variation that identifying species was confusing.
He is setting the stage for the next two chapters.
c. What was he trying to show in Chapter III, Struggle for Existence?
Given that most organisms have high reproductive rates, all individuals cannot
survive. Finite food and space limit numbers; also, predation, parasitism,
disease, competition, climate reduce populations.
d. Why was establishing that variation exists among individuals of all species
and demonstrating how selection works in domestic animals and plants so crucial
to the main ideas in Chapter IV, Natural Selection? What were these ideas?
The key to understanding the mechanism of natural selection is recognizing that
individual variation exists among organisms within a species, resulting in
differential survival and reproduction. Most people could see this most easily
with practical examples. Thus, there is a relatively greater contribution of
offspring from the individuals that have certain variation, and their offspring will
in turn have similar traits. Thus, certain “favored” variation spreads through the
species over time, which leads to “descent with modification” or evolution over
time.
8. (10 pts) More questions based on On the Origin of Species
4
a. This diagram from Chapter IV, Natural Selection, depicts what process? This
diagram illustrates how species may arise from other species, leading to the
process of “descent with modification.”
b. Referring to Chapter VII, Instinct, what does Darwin mean by “instinct”? What
is his main point in this chapter? Instinct is used to mean “behavior” by
Darwin. His main point is that behavior is a trait that can be sorted by selection
just like morphological traits.
c. Referring to Chapter XIII, Mutual Affinities of Organic Beings, what is by the
statement, “By means of descent with modification, all the great facts in
morphology become intelligible. “ These “great facts” include descriptions of
anatomy, morphology, and embryology. So Darwin realized that common
descent and degree of relatedness from the process of “descent with
modification” explains similarities and differences among these features in
species. The more closely related the species, the more similar.
9. (3 pts) a. What theories account for the formation of the universe and the
formation of our solar system?
The Big Bang theory explains the formation of the universe. The Nebular or
Condensation hypothesis explains the formation of the solar system.
b. What is the relative abundance of normal matter, dark matter, and dark
energy in the universe?
The relative abundances are: 4.6% normal (baryonic) matter, 23.3% dark matter,
72.1% dark energy.
10. (6 pts) a. What was the composition and fate of the first atmosphere on earth?
The first atmosphere was composed of hydrogen and helium. The gravity was
too weak to hold it, coupled with other forces such as heat radiating from the
earth and the solar wind. (2 pts)
b. What was the composition of the second stable atmosphere?
The second atmosphere was composed of H O, CO N H
CH CO NH
2
2 2
2
4
3
Cl H S. (3 pts)
2
c. What was the general chemical property of the second atmosphere (hint:
redox)? Catalyzed reduction reactions: a reducing atmosphere. (1 pt)
11. (4 pts) List four possible places/conditions were organic molecules were first
synthesized abiotically? (1 pt each)
i. Outer space (exogenous delivery) brought in by meteors
ii. Hydrothermal vent systems or volcanoes
iii. Clay substrates
iv. Oceans and ponds
12. (10 pts) What are two sources of data that demonstrate that simple organic
molecules can readily be synthesized abiotically under roughly the conditions that
existed on the young earth or in outer space? Explain both of these forms of evidence.
i. One form of evidence comes from the analysis of organics on meteors
that have fallen to earth, such as the Murchison meteor. This meteor carried
5
many amino acids, urea, and other simple organic molecules, indicating that
these may be easily synthesized in space. Space has precursor gases and high
energy sources, as existed on the early earth. (4 pts)
ii. The other form of evidence includes laboratory synthesis of organics
under conditions believed to have existed on early earth. These conditions were
replicated in the laboratory experiments of Stanley Miller. He circulated
ammonia, methane, hydrogen gas, and water in an apparatus with an electric
spark discharged every few seconds but all day for an entire week. Circulating
cool water condensed gases, and samples were taken from liquid water at the
bottom of the apparatus and analyzed. The experiment generated simple
organics similar to those from the Murchison meteor. (6 pts)
Also, molecules from the five basic groups of organic molecules—Aldehydes,
sugars, purines and pyrimidines, fatty acids, and pyrroles and porphyrin rings—
have been synthesized in the laboratory under conditions simulating the early
earth and reducing atmosphere more recently. More complex macromolecules
can be synthesized from these.
13. (3 pts) Explain what is meant by the principle of self-assembly when it comes to the
structure of protocells.
The proposed models for protocells are composed of somewhat complex
structures that spontaneously self-assemble from simple organic molecules,
because of basic chemical interactions.
14. (10 pts) Briefly describe the structure and function of the following protocell models
in terms of self-assembly and chemical organization. Which have the most potential, in
your opinion, as an ancestral protocell?
a. coacervate: These form spontaneously in water. They form from clumps
or aggregations of macromolecules with a rigid shell of water, and can be very
stable over time. They are selectively permeable and capable of conducting
metabolic reactions, if proteins have enzymatic activity. They can grow and
fragment, giving rise to more coacervates. (3 pts)
b. proteinoid microsphere: These microspheres form when dry mixtures of
amino acids are heated to high temperatures and cooled in water. They have
double membranes, and a composition that departs from the original mixture.
The membranes are selectively permeable. The microspheres can bud off. ( 3
pts)
c. liposome: These are biphosplipid layers, like cell membranes, that have
formed vesicles. The layers can capture proteins within, which can have function
and determine permeability. (2 pts).
d. clay vesicle: Clay-coated bubbles can form vesicles after the bubbles
pop. Montmorillonite clay in particular can catalyze reactions such as
polypeptide bonds and nucleotide bonds. (2 pts)
6
15. (8 pts) Given that the protocells are not living organisms, explain how a sort of
natural selection could function and improve their efficiency. Use the following parallels
to develop your argument.
 variation within populations: Protocells differ in type and structure. (1
pt)
 population growth: The number of protocells have grown over time by
protocells accumulating and budding and fragmenting from taking in
materials from the surrounding medium. (1 pt)
 struggle for existence: With so many protocells, organic molecules
and salts in the medium become scarce. This slows growth and
reproduction. (2 pts)
 natural selection: The protocells best able to take in materials, or
those that can catalyze reactions and synthesize scarce molecules
are those that prevail by continuing to grow and “reproduce” where
the others cannot. (2 pts)
 descent with modification: Every step in improvement of function and
efficiency within a protocell results in its increase and the
replacement of other protocells. Changes occur over time in the
protocell structure and function.