BAC Report- 1st Midterm

Hello Everyone,

The BAC met this afternoon to discuss the comments you had regarding the test questions from the first exam.

Since this morning, I realized that I had incorrectly posted the answers to two questions

a) 35 Blue and 38 Green

 - the answer was listed as b, but the correct answer is d

b) 48 Blue and 50 Green

 - the answer was listed as c, but the correct answer is d

In addition, they brought 5 questions forward to me for consideration.

1) Question 2 Blue and 2 Green

I think that the correct answer for this question is a) selfish trait.  The high density of spines on cactus leaves is a characteristic of that leaf (i.e., a trait).   Because that trait decreases the probability that the leaves are eaten it is a trait that increases the fitness of the cactus.  Therefore, by definition they are "selfish traits".

The BAC argued (vigorously) that answer c) natural selection was an equally good answer.  I disagree with that for one main reason.  According to the definition of natural selection.... natural selection is a "process".  The spines on the leaves of cactus are not a process, therefore this can not be the correct answer.

It is true that the selfish traits were produced by the process of natural selection.  But I think that it is important to distinguish between the process and the trait.

decision- answer a remains the only correct answer.

2) 16 Blue, 21 Green

I think that the correct answer to the question is (c) because male gametes are smaller than female gametes many more male gametes than female gametes are produced.

The BAC argued (very vigorously) that answer e) female reproductive success is resource limited was an equally good answer.  I disagree because the reason that males compete is not determined by the factors that limit female reproductive success but by the fact that there are so many more male gametes than female gametes produced.

decision- answer c remains the only correct answer

3) 42 Blue, 44 Green

I think that the correct answer to this question is d.

An organism acting altruistically towards a non-relative is explained by reciprocal altruism.  In reciprocal altruism, an individual "chooses" to be altruistic because its individual fitness is great when altruistic than when selfish.

Because the organism is helping a non-relative there is no chance for inclusive fitness (inclusive fitness = zero)

thus, because answer a is not true and both answers b and c are true, answer d is the best answer.

decision- d remains the only correct answer.

4) 46 Blue, 47 Green

The two questions related to this description (Blue 45 and 46; Green 46 and 47) were written to be independent questions.

Thus, I intended that the carrying capacity of the populations in question 47 to be unknown.  Without knowing the population sizes of the two species it is impossible to know which species has the highest population growth rate.  Thus, I thought the answer to this question is d.

However, it is easy to see how someone would conclude that N = 10 individuals from question 45 Blue or 46 Green carried on into the following question.  If this is true then there is enough information to answer the question.  Plugging N, rmax and K  for each species into the logisitic growth equation shows that the population growth rate of sparrows is less than the population growth rate of grasshoppers.  Thus, answer b would be the correct answer.

decision- both b and d will be considered to be correct answers to this question.

5) Question 49 Blue, 29 Green

I think that the correct answer to this question is c.  The Singaporean government is trying to encourage women to decide to have more children.

The BAC argued (very vigorously) that answer a) was an equally good answer.

When I used the term "resource-limitation" I meant that the females had so many resources that they were incapable of reproducing (this is the way the term is used in biology).  However, it was clear to me that a student who interpreted "resource limitation" in a different way could have chosen a as an equally good answer.

decision- both a and c will be considered correct answers to this question

The correct answers are now shown in the "First Midterm Answer Keys" post on the blog.

I would like to thank the BAC for spending their time and effort helping to assure that the testing process is as fair as possible.  Make sure you give your BAC reps a little love as well!