BEP 210 A MIDTERM EXAM
Regrades can be requested if submitted in writing to the TA's by April
2. Regrade requests must explain why you think there was a grading error
based on the answers provided to you in the online answer key. If you
find simple math errors they can be brought to the attention of the
TA's after class and dealt with at that time. Math errors will be
corrected between now and April 2 and do not require a written regrade
request. We reserve the right to regrade other questions.
SHORT QUESTIONS:
1) Put the following three milestones of the Big Bang in chronological order: decoupling, baryogenesis, Big Bang nucleosynthesis. ( 1 point)
- baryogenesis, BBN, decoupling
Then explain briefly what happened at each milestone. (about 1 point each)
-baryogenesis : a small excess of quarks over antiquarks is created .(Also a small excess of electrons over positrons)
-B B N : protons & neutrons combine to make Deuterons and then He4 nuclei.(Small amount of He3 and Li6 are also made)
-decoupling : Neutral atoms form for the first time (neutron Hydrogen, deuterium, helium) Photos are decoupled-don't interact with matter any
more- make the CMB
2) If the universe were infinite in space, had existed for an infinite amount of time, and were homogeneous (on large enough scales), how would the night sky look? (1 point)
- This is Olber's paradox, sky would be completely white (light)
Why? (2 points)
- Every space would be filled by light from some distant star.
How does the theory of the Big Bang help explain how the sky actually looks? (2 points)
-The BB says our universe has only existed for a finite time, so light hasn't had time to get to us from very distant stars . This explains the existance of lots of darks places in night sky. ( * the sky is may be filled with stars but we cannot see them...)
3) For each of the four fundamental forces, name one effect that it, and no other force, can produce. (almost 1 point for each force + 1 point for naming the 4 forces)
- Gravity : binds galaxies , solar system together or
binds earth together or
compresses stars and sets them hot enough to start nuclear fusion or...
- Strong: binds quarks inside p and n or
bind nuclei together (bind p and n inside nuclei) or
provides main source of energy for sun, stars today
- EM : binds e's and nucleus in atoms or
creates Coulomb's barrier in nuclear interaction or
binds atom together or...
- Weak : changes particle type or
neutron decay or
allows sun to work by p+p-> D or
may cause baryogenesis
4) In class, we saw a picture of the fluctuations in the Cosmic Microwave Background. There were small bright regions (orange and red) interspersed with small dark regions (blue and dark blue). What is the significance of the dark regions for the development of the universe? (5 points)
-the dark regions are places where the universe was slighlty more dense at the time of decoupling.
After that time, these clumps grew and became galaxies, clusters of galaxies.
5) In Martin Rees's book, Just Six Numbers, he discusses the number "N", which describes how much stronger electromagnetism is than gravity. N is an enormous number. Imagine another universe, in which N is still very big, but is significantly smaller than the N of our universe. Explain ONE reason why it would be unlikely for life to evolve in such a universe. (5 points)
- if N were less gravity would be stronger... (1 point) so some reasons why it would be unlikely for life to evolve
( i) Stars would be very tightly compressed, very hot and so the fuels would burn very quickly. Then, not enough time for life to evovle.
(ii) Stars would be very close together, planets would get knocked out of orbit...No stable conditions for life to evolve.
(iii) Gravity very storng relative to ours and would force living things to be very small...hard to get big, complex life.
LONG QUESTIONS:
1) (a) What is the doppler effect? (2 points)
- Doppler effect is an effect on any repeated, travelling "disturbance" (a wave). When source moves away from (towards) you frequency you observe is less(more) than the normal (emmited one)
why does it occur? (2 points)
- I f source is moving away, each successive wave takes longer to reach you than previous one- time between arriving waves is spread out.
(b) What is Hubble's law? (2 points)
- Hubble's law says distant galaxies are moving away from us with a speed proprtional to their distances.
how it has been verified? (1 point)
- It has been verified by Doppler effect on light from distant galaxies. The red -shift in the frequency of their light is proportional to their distance. that means that their speed (according to Doppler effect ) is proportional to their distance from us.
(c) Why does Hubble's law imply that there was a Big Bang? (3 points)
- Galaxies farther away are moving away faster. In past everything was closer and distant things were a lot closer than now (like the car race example). So everything was on top of everything else, just like is described by BB theory.
2) A proton is moving towards a deuteron (deuterium nucleus). The proton "sees" an "energy well" of a certain distinctive shape. Sketch a picture of the energy well and explain the origin its key features, using what you know about the strength, range, and direction (attractive or repulsive) of the relevant fundamental forces. (6 points)
- The deep well is caused by the attractive but short range, strong force. If p &D get close enough it will pull them together, like falling in well.
Coulomb barrier is caused by repulsive, long range but weaker e/m force. Because e/m is long range force it is the first thing that the proton "feels". It is a barrier because the force is repulsive. But if p gets close enough to D, so that short range, strong force can act, the strong force will win and pull them together.
Using your picture, explain why protons and deuterons inside a star will only combine if the temperature is high enough. (4 points)
- To combine, the p has to start with enough kinetic energy to get over coulomb barrier. It has this energy of motion only if star is hot enough.
Dr. Wysession's geology questions:
# 6. What are planetesimals, and what role did they play in the formation of the solar system?
Planetesimals are the seeds of planets (other terms accepted included "proto-planets", "baby-planets", "clumps of stellar dust", etc) that formed from the dust and ice present in the protoplanetary disk. They started as dust balls held together by weak intermolecular forces (Van der Waals forces) but as they grew bigger, their gravity became significant and accretion accelerated. This accelerated accretion culminated with the Late Heavy Bombardment, where large planetesimals collided with each other catastrophically to ultimately produce the planets of our solar system as we know them today.
# 7. Planets in the inner solar system (Mercury, Venus, Earth, Mars) formed with very few gases, liquids, and ices (when compared to outer solar system planets). Why?
By definition, planets of the inner solar system are closer to the sun. It follows that while these planets were accreting, they were closer to the proto-sun. This proximity to the proto-sun meant that it was warmer where the inner planets were forming than it was where the outer planets were forming. The heat from the proto-sun prevented the more volatile materials (things like hydrogen, helium, water, methane, etc-things we see as liquids and ices on the outer planets) from condensing on the inner planets. The inner planets therefore accreted from the leftover material-rocks and metals. The outer planets were not heated very much so these planets incorporated all of the available materials into their makeup-rocks, metals, ices, liquids, and gases.
# 8. The earth and its moon have different surface area-to-volume ratios. What implications does this have for the different geological histories of each?
The earth is much larger than the moon. It follows that the earth has a much smaller surface area-to-volume ratio and will, therefore, cool much slower than the moon. The implications of this are that the moon should have cooled very rapidly, ending any geological activity fairly early in the solar system's history while the earth should still be cooling and is therefore, still geologically active. This is in fact what we observe. The moon has been geologically dead for a long time as evidenced by its heavily cratered surface. The earth on the other hand, is still geologically active-plate tectonics is still currently happening because the earth is still cooling. While erosion and resurfacing have erased impact craters, the earth's rock record preserves a very long and rich geologic history created as a result of the earth's slow cooling processes.
# 9. Explain what a "subduction zone" and a "mid-ocean ridge" are, and what roles they play in the process of plate tectonics.
A subduction zone is a convergent plate boundary where an old (~200 Ma), cold ocean plate sinks down into the mantle. Subduction zones destroy old ocean crust and are widely associated with earthquakes and volcanoes. Their occurrence corresponds to the downwelling of a mantle convection cell.
A mid-ocean ridge is a divergent plate boundary where new ocean crust is created. They form continuous chains of undersea volcanoes that are also associated with earthquakes. Mid-ocean ridges are where the hot return flow of mantle convection reaches the surface.
# 10. Explain why a bowl of hot miso soup is like the Earth. Explain why this would be more so if the bowl of soup were in a microwave oven (at a very low setting).
A hot bowl of miso soup is like the earth because it convectively cools. When the cover is removed from the soup, the surface radiates heat to the air like the earth's surface radiates its heat into space. This produces chilled sheets on top of the soup analogous to the chilled ocean crust of the earth. At some point, these sheets become less buoyant than the underlying soup and begin to subduct as the earth's oceanic plates do. This results in a return flow of warmer soup/mantle rock to the surface.
This analogy is better if we put the soup in a microwave. A low setting is required because we don't want the soup to boil over (that obviously isn't what we see the earth doing). We know that the earth is being internally heated by the decay of radioactive isotopes. A microwave heats food by vibrating the water molecules in the food and is therefore a way we can induce internal heating in our soup.
LONG QUESTIONS
# 3. Explain how the following characteristics of our solar system agree with the currently accepted nebular hypothesis:
a) All of the planets revolve in the same plane, in the same direction, around the sun.
b) Most of the planets rotate in the same direction (which is the same direction they revolve around the sun).
c) The planets have nearly circular orbits that do not intersect (with the exception of the furthest two, Neptune and Pluto).
d) The surfaces of inner planets like Mercury and Mars are covered with craters, and show evidence of some very large impacts.
a + b : I considered these two parts adequately explained if you included in your response some description of how gravity interacted with the fact that the nebular cloud was spinning to produce a fried egg shaped protoplanetary disk. The shape of the disk explains the ecliptic and invoking the conservation of angular momentum answers both rotation direction questions.
c + d : These two parts could have been answered together depending on how you worded your description of planetary accretion. The Late Heavy Bombardment eliminated any planetary bodies with intersecting orbits (with the exception of the farthest two-something easily explained) while also leaving behind evidence of this violent period of accretion on Mercury and Mars (the other planets got bombarded too but resurfacing has destroyed much of the evidence).
# 4. Heat can be transferred through conduction, convection, and radiation. Briefly describe how each of these works, and then tell where in the earth each of these is important.
Conduction: moves heat by passing it from molecule to molecule by direct contact
important at the core-mantle boundary and in the crust
Convection: moves heat by moving the material the heat is in-results in a convection cycle
important in the mantle and the outer core
Radiation: moves heat by emitting it as electromagnetic waves
important at the earth's surface
Answer key to Dr. Goodenough's biology based questions:
Short questions:
11. What does the Hox gene family specify in all animals, and what, in addition, does it specify in most modern vertebrates?
In all animals Hox specifiy the identity of regions along the main body axis (Head to toe). It does not only specify head or the tail. These were two example from class.
In verts Hox have also been recruited for use in limb development. Here the specify the three regions of the limbs (upper arm/leg, lower arm/leg, and hand/foot)
12. What is meant by a conserved gene? Explain the logic involved in using conserved genes as evolutionary clocks?
A conserved gene is a gene that is found in many species because it was inherited from a common ancestor. Since all organisms share a common ancestor, all organisms will share some genes. Genes do not appear in different lineages or organisms, they are there due to common ancestery. The presence of conserved genes does not necessarily mean that it leads to an increased fitness in organisms with that gene. It may appear selectively neutral in all organisms possessing it once it becomes established and passed on from the common ancestor.
Mutations in these conserved genes allow us to use them as evolutionary clocks since we know that more closely related organisms will share more in common that distantly related organisms. Evolutionary biologists do not create species level evolutionary trees based solely on the presence or absence of conserved genes.
13. How does shape change participate in the activity of a receptor OR an enzyme?
Receptor: A ligand binds to the receptor, which leads to a conformation change both inside and outside of the cell membrane. Outside of the cell this helps to bind the ligand and receptor. Inside shape change triggers a signal transduction cascade. Here you need to point out that there are shape changes both inside and outside of the cell for full credit.
Enzyme: First one ligand binds to the enzyme, which induces a shape change.
This shape change opens another active site in the enzyme that then binds another ligand and again induces another shape change in the enzyme. This shape change brings the two proteins in close proximity to one another and a bond is formed between them. This new molecule is released and the enzyme returns to its original state.
14. Why is the tensility of a microtubule considered a first-order and not a
second-order property?
First order properties: reliant on the shape and properties of the molecules
Second order: shape playing out through time with initial and boundary conditions
15. Give two ways that an amoeba's awareness of/response to food is the same as
an embryonic neuron's awareness of/response to another neuron.
Both have aspects of short term responses to stimuli where they use receptors to sense their environment which then trigger signal transduction cascades which lead to a response. It was not sufficient just to say that there is a gradient of the stimulus with out mentioning the details of the system such as actin filaments or the use of receptors.
Long questions:
6. Describe briefly the sequence of events offered in class and/or in The Sacred Depths of Nature for the evolution of the bacterial flagellum, and explain why it is untenable to claim that the flagellum was "designed" because it observed to be "irreducibly complex."
The bacterial flagellum began as a membrane bound channel that excreted some sort of molecule. Then a random mutation caused an accessory protein to bind to the channel causing it to act more efficiently. It was thus selected for in the population of bacteria possessing it. As a side effect this channel began to spin due to the extra protein. Later on anther mutation occurred that placed a fibrous protein on the outside of the channel. This protein spun due to the earlier mutation and thus allowed the bacteria to move. Subsequent mutations have made this an even more complex and better functional mode of bacterial mobility. The essence of this answer is that the progress occurred through step-wise mutation and selection.
This is not an example of irreducible complexity because when put in a historical perspective this highly integrated unit was assembled in a step-wise process of addition and subsequent modification of the entire unit. So just because the modern flagellum will not work without all of the pieces, doesn't mean that past flagella would not have worked at all. Irreducible complexity does not utilize a historical perspective. Irreducible complexity in one of the oldest arguments against Darwinism but its logic is inherently flawed.
2. Explain, at the molecular level offered in class, how a simple two-neuron
synapse works and how this signal-transduction scheme is different in brains.
Here I was specifically looking for the details of the interactions that occur around the synapse including functions of the channels, receptors, and secretions.
First, a stimulus triggers a sensory neuron, which creates an action potential that moves the length of that neuron (1pts) until it reaches a synapse (1pt) shared with a motor neuron. As channels on the first neuron open ions rush (2pts) in signaling the release of neurotransmitters (2pts) into the synapse. These are picked up by the receptors of the motor neuron signaling for more channels to open and the response to travel up the motor neuron to the CNS (1pts).
The brain is unique in that each neuron has 100's to ~1000 neurons connecting at each synapse. It is the combinatorial nature of positive and negative inputs into each synapse that leads to a coordinated response to a stimulus (3pts).