Download Midterm exam

ASTR/GEOL-2040-001:
Midterm exam
Name: ......................................................
Search for Life in the Universe (March 2, 2017)
Note: there can be multiple (even more than two) correct answers! Mark them with a circle.
1. Which of these gases was/were used in the original Miller/Urey experiment?
O2
CO
CO2
SO2
H2 O
H2
NH3
NO2
N2 O
CH4
2. What kind of macromolecule is
(a) lipid
(b) polysaccharide
(c) protein
(d) nucleic acid
(c) protein
(d) nucleic acid
3. What kind of macromolecule is
(a) lipid
(b) polysaccharide
4. The age of lunar rocks has been determined by measuring the
(a) isotope ratios
(b) zircon crystals
(c) mineral content
(d) total uranium content
5. What is the third-most abundant element in the Earth atmosphere
(a) oxygen
(b) carbon
(c) neon
(d) argon
(e) potassium
6. A blue-green cell is floating in a petri dish of ocean water. When exposed to sunlight, the cell
is observed to grow, multiply, and excrete oxygen gas – these behaviors end shortly after the
light source is removed. What kind of organism is this cell?
(a) photolithoautotroph
(d) chemoorganoheterotroph
(b) chemolithoautotroph
(e) chemolithoheterotroph
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(c) photolithoheterotroph
7. A gray bacterium is found in the interior spaces of a rock from a deep gold mine in South
Africa. The cell is always found to be growing, multiplying, and excreting carbon dioxide gas
– moreover, the rocks mineral structure is found to be depleted in iron the longer the bacterial
colony lives. However, when the rock is cooled to cool room temperature, all cells are seen to
die. What kind of organism would you expect this bacterium most likely to be?
(a) chemolithoautotroph, psychrophilic
(b) chemolithoautotroph, psychrophilic
(c) photolithoheterotroph, thermophilic
(d) chemolithoheterotroph, thermophilic
8. What kind of macromolecule is
(a) lipid
(b) polysaccharide
(c) protein
(d) nucleic acid
9. Which of the following rock types have been found on the Moon?
(a) granite
(b) basalt
(c) marble
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(d) sedimentary rock
10. The discovery of 4.4 Gyr old zircons has been regarded as evidence for
(a) sterilizing impact
(b) stable continents
(c) early water oceans
(d) photosynthesis
11. In contrast to the black smokers, alkaline vents produce mainly (multiple answers possible!)
CO2
12. In the reaction
N2 O
H2 S
H2
CH4
CO2 + 4H2 → CH4 + 2H2 O,
the energy comes from: (sunlight/molecules), so the relevant prefix is (photo/chemo)
the electron donor is: ......................, which is (organic/inorganic), so (organo/litho),
and the carbon source is: ......................, which is (organic/inorganic), so (hetero/auto),
and so it is a: ..........................................troph.
13. A 10 g mixture of two unknown chemical powders, one red and one green, is stirred into a 250
mL beaker of water. After one minute of stirring, the green substance has completely dissolved
but the red powder has collected on the bottom of the beaker. What could be said about the
molecular structure of both substances from this experiment?
(a)
(b)
(c)
(d)
Both substances are non-polar.
The green substance is polar; the red substance is non-polar.
Both substances are polar.
The red substance is polar; the green substance is non-polar.
14. Would we consider the detection of an oxygen atmosphere on another planet as a likely sign of
extant extraterrestrial life?
(a)
(b)
(c)
(d)
No – oxygen is just another element.
Yes – oxygen is a requirement for any kind of life.
No – oxygen is a sign of extinct life forms.
Yes – oxygen is highly reactive and needs to be actively replaced through photosynthesis.
15. Earth’s first atmosphere was chemically similar to those of Mars and Venus. How did our
current atmosphere become so drastically different from our nearest neighbors’ ?
(a) Life – early photosynthetic organisms consumed CO2 and exhaled O2 .
(b) Volcanism & Tectonics – Earth’s numerous volcanoes expel O2 gas while plate tectonics
undertakes carbonate rocks.
(c) Asteroids – Impacts from space debris converted CO2 into O2 by impact ablation and
high energy explosions.
(d) Water – Earth’s liquid oceans provide a natural filter that strips the carbon from CO2 ,
leaving the O2 .
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16. Both RNA and DNA can be used to store genetic information. Why is DNA the preferred
information storage molecule?
(a)
(b)
(c)
(d)
DNA’s double helix is more chemically stable.
Thymine in DNA is superior to uracil in RNA for encoding information.
RNA’s single strand structure is unreadable by ribosomes.
Only DNA is capable of making more of itself.
17. “RNA world” refers to
(a) the possibility that life migrated from Mars,
(b) the idea that RNA was life’s genetic material before DNA,
(c) the idea that early life was made exclusively from RNA, needing no other organic chemicals
18. Why does Venus have so much CO2 in its atmosphere?
(a)
(b)
(c)
(d)
Venus
Venus
Venus
Venus
has extreme volcanic activity leading to significant outgassing,
has no rain water allowing CO2 to be returned to the mantle,
is no magnetic field allowing the CO2 to be removed by the solar wind.
has a strong greenhouse effect owing to its proximity to the Sun.
19. Stromatolites are
(a)
(b)
(c)
(d)
iron-reducing lithotrophs extracting energy from the rocks they are living on,
photosynthesizing cyanobacteria growing on top of each other,
hydrothermal alkaline vents harboring methanogens that life of hydrogen and CO2 ,
sedimentary rocks in Western Australia where the oldest microfossils have been found.
20. What do geologists mean by the “boring billion”?
(a) The time when the ozone layer was too thin to protect life from hazardous UV radiation
and life could only survive under water.
(b) The epoch during the Archean eon before photosynthesis led to a rapid growth of atmospheric
oxygen.
(c) The snowball Earth event when most of the life forms on Earth got extinct under a thick
layer of ice.
(d) A time during the Proterozoic eon when atmospheric oxygen stagnated at about 1% of
the present level.
21. “Snowball Earth” refers to
(a) One in a series of deep ice ages that occurred > 0.5 Gyr ago.
(b) The idea that Earth would be frozen without greenhouse effect.
(c) Any of the ice ages that occurred in the past few million years.
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22. List some key properties of life as we know it.
23. The second law of thermodynamics states that the degree of disorder of all of the Universe can
only increase. Explain what life does to the degree of disorder and why this is not in conflict
with the second law of thermodynamics.
24. Explain why the concept of Darwinian evolution requires that (i) the number of individuals
being produced must be greater than the number of those that can survive, and (ii) there must
be struggle for existence, e.g., through limited resources.
25. Name the three basic rock types and explain them in a few words.
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26. Iron-reducing bacteria make their biological living by performing the following reaction
2H2 O + Fe2 O3 → 2Fe(OH)2 + 21 O2 .
In this reaction, iron (Fe) plays the same role that inorganic carbon (C) would play in “regular”
biological reactions like photosynthesis. (Thus, instead of a carbon source, look for an iron
source instead when making your choice.)
• With this in mind, determine what kind of -troph this iron-reducing bacteria would be.
• Justify each of the prefixes used in your answer.
27. A sample of lunar rock had 80 mg of 40 K at its formation. Assume for its half-life 1.25 Gyr
and that 90% decays into 40 Ca and 10% into 40 Ar.
• How much
40 K
• How much
40 Ca
will be produced after 1.25 Gyr?
• How much
40 Ar
will be produced after 1.25 Gyr?
will be left after 1.25 Gyr?
• After 1.25 Gyr, what is the total weight of
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40 K, 40 Ca,
and
40 Ar?
28. Chemically speaking, Si is the most abundant element on Earth’s crust. Why would we still
expect any life on another planet to be carbon based?
29. A tree grows, literally, from thin air — all the carbon that goes into a plant’s roots, bark, and
leaves comes from CO2 in the atmosphere, gained through photosynthesis.
• CO2 has a density of 2 g/L, so how many liters of CO2 are needed to grow a redwood tree
106 kg, of which 50% is carbon?
• Assume you exhale 100 liters of CO2 per hour, how long would it take you to generate
the required amount of CO2 ? [Hint: for the purpose of this estimate, assume that 1 year
has 105 hours.]
30. On the Earth, the carbon dioxide cycle between atmosphere and mantle operates in such a way
that it regulates its temperature. Explain how this works and why rain water and carbonate
minerals are important for the CO2 cycle.
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31. From DNA to a protein
(i) Given the DNA codon sequence TAC GCT AAG AAC TAT CCG TCA ATT, determine
the corresponding RNA match.
(ii) Determine the encoded amino acid sequence,
(iii) Identify a mutation that would produce the same protein.
(iv) Identify a catastrophic mutation to the fourth codon that would terminate the peptide.
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