Key -- BIOL 103 TEST 1       2008

  

 

For quantitative questions, SHOW ALL YOUR WORK or receive zero credit.

Constants that may or may not be useful:


Pi (π) = 3.14159

Planck’s constant = h = 6.626 x 10-34 Joules sec

Frequency of a light photon = 1015 Hz (1/sec)

Wavelength of a light photon = 0.5 x 10-6 meters

Radio wavelength = 5 x 103 meters

Speed of light = c = 3.00 x 108 meters/sec

 

1. (5 pts) How and where in the universe were most of the atomic nuclei in our bodies originally formed? 

 

The elements of atomic nuclei were formed through fusion reactions in ancient stars. Hydrogen fused to form helium, then once the helium was depleted, there formed large elements including carbon, nitrogen, and oxygen. During the formation of larger elements, the stars developed into red giants. Sufficiently large red giants exploded as supernovas, sending the elements across the galaxy, where they collected within planets to form nuclei of carbon, nitrogen, and oxygen. Hydrogen came from our own star, the sun, but our sun is too young to have formed higher elements. 

 

2.  (20 pts)  Mr. Spock picks up a Vulcan-loving Kribble and releases it on a planet without natural predators.  A Kribble expends 86% of its energy producing 3 offspring every 10 hours, then dies.

 

A.  After a week on this planet (7 days, 24 hours per day), how many Kribbles will there be? 

 

 Nt = N0 Qt/d = 1 Kribble x 3(7 days)(24 hours/day)/10 hours = 1.03 x 108 Kribbles

 

Note: Any answer ending in ".1" lost points because you can't have one-tenth of a Kribble.

 

 B.  Despite the lack of predators, how will other phenomena curb the Kribble population?  Explain.

 
The Kribbles will run out of food, and thus be unable to continue exponential reproduction. Their growth may be slowed by disease-causing microbes and parasites, which spread faster in more crowded populations; and by accumulation of toxic wasteproducts from their own bodies. 

3. (15 pts) In Well’s The Time Machine, and in Vonnegut’s Galapagos, future humans evolve smaller brains. 

A.  For each story, explain the key reason why and how smaller brains evolved.


In The Time Machine, the Eloi evolved smaller brains through a process called degenerative evolution. Because the Eloi had all their needs met by the Morlocks, they lost the selective pressure to maintain large brains to manufacture the things they needed. The Morelocks also seem to have evolved smaller brains; the reason for this is not addressed. 

In Galapagos, the smaller brain size of future humans seems to evolve through a combination of degenerative evolution (the lack of need for big brains in the simple island environment) and natural selection for narrower, streamlined head size for swimming and fishing. Vonnegut also argues that the original human brains had evolved to a dead-end of extreme size, to a degree that the outsized brains actually detracted from human reproduction.

 

B.  For the two stories, explain how the principles of “human evolution” are similar, and how they differ.

 

With respect to brains, the Time Machine mainly presents degenerative evolution, whereas Galapagos suggests a combination of natural selection and degenerative evolution. In The Time Machine, natural selection acts on other parts of the body, such as the owl-like outsized eyes of the Morlocks.

 

4. (15 pts)  What is a “population bottleneck”?

A.  Explain how a population bottleneck accelerates evolution, including a specific example.

 

A population bottleneck occurs when a relatively small population becomes isolated. The small population size increases genetic drift, allowing rapid shifts in gene frequency. When natural selection acts upon a small population, it may evolve rapidly into a new strain or species. An example is the Galapagos humans, who evolved rapidly into furry creatures because Akiko's genes spread, and because genes for narrower head size spread through the human descendents.

 

B.  Suppose a virus infects a population of 500,000 Tribbles, and after three days only 200 remain.  What is their half-life (halving time, time for half to die off)?

 

Nt = N0 Qt/d


200 = 500,000 x (0.5)t days / d days Solve for d:

log (200/500,000) = (t/d) log (0.5)

d = t x log(0.5) / log (200/500,000)

d = 3 days x 0.08859 = 0.265 days = 6.38 hours


 5.  (15 pts)  Lemmings have various options for reproductive success.

 

A.  Describe two alternative reproductive strategies available to individual lemmings. 

 

When the population level reaches a high density, Individual lemmings may:
-- Disperse in all directions, diminishing population density, and finding improved habitat with greater resources. Offspring will inherit genes that trigger future dispersal.

-- Disperse in a direction that leads to jumping into the fjord; a risky move, but one with the potential for reaching highly favorable new habitat. Offspring will inherit genes for dispersal and strong swimming.

-- Stay put, while the others disperse. Eventually, the local habitat improves. Offspring inherit genes that increase survival through lean times.
(Any two of the above three) 

 

B.  Explain the selective advantage of each type of lemming behavior.


The advantage of dispersing is the likelihood of improved resources with lower population density.
The advantage of jumping in the fjord is the chance of finding exceptionally good habitat, with no competitors; but the risk of death is also greater.
Staying put may be the least risky, and conserves energy, although it requires survival through a time of depleted resources. 

(10 pts) Marfan’s disease causes unusual bone length plus heart defects; it is occasionally diagnosed in basketball and volleyball players.  Marfan’s is caused by a dominant gene.  In the United States, 200,000 people have this disorder, out of a total population of three hundred million.  What is the allele frequency of the Marfan gene?

200,000/300,000,000 = 0.0006667, the frequency of single-dominant plus double-dominant individuals showing this disorder (p2 + 2pq)

The frequency of unaffected individuals (q2) is then given by:
1 - (p2 + 2pq) = 1- 0.0006667 = 0.9993333
The frequency of the normal allele (q) is then squareroot(0.9993333) = 0.9996666
The frequency of the Marfan allele (p) is then (1 - q) = 0.000333 = 0.0333%

 

7. (10 pts) The first few children of the Galapagos colony spoke mainly Kanka-bono; a million years later, no human descendents spoke at all.  Why?  Explain in terms of genes and/or environment.

 

The first few children spoke mainly Kanka-bono because most of their mothers were Kanka-bono; thus, the children learned language in the Kanka-bono environment.

A million years later, degenerative evolution had eliminated the ability to speak at all. This effect involved change in the allele frequencies of genes.

 

8. (5 pts) Birds often assist the reproduction of family members.  Which relative is a male bird more likely to assist: an aunt, or a cousin?  Explain why, showing numbers.

 

Birds exhibit "kin selection" -- that is, they will offer greater assistance to individuals of greater genetic relatedness to them. A male bird shares 0.5 x 0.5 = 0.25 of his genes with his parent's sister. He shares 0.5 x 0.5 x 0.5 = 0.125 of his genes with his cousin. Therefore, a bird is roughly twice as likely to help an aunt raise chicks as to help a cousin.

 

9. (5 pts) One of Barlowe’s green aliens obtains energy through photosynthesis.  How many photons would it need to gain as much energy as from eating a slice of bread (320 kilo-Joules)?


Calculate the energy per photon of light:

E = hc/lambda
= (6.626 x 10-34 Joules sec) x (3.00 x 108 meter/sec) / 0.5 x 10-6 meters
= 3.98 x 10-19

Joules

Divide the amount of energy in one slice of bread (320 kilo-Joules) by the energy per photon:

Number of photons = 320 x 103 Joules / 3.98 x 10-19Joules per photon
= 8.04 x 1023 photons