@xxjmodxx I was also confused by that one, but I also said “anaphase”. Pretty sure the question asked which of the phases will be most disrupted, and I thought during anaphase the chromosomes cannot be separated from the metaphase plate due to a lack of spindle fibers. But I think technically the spindle fibers wouldn’t have formed during prophase, THUS RESULTING in the disruption of the anaphase. There is a causal relationship. But I still chose anaphase because I guessed that’s what the test maker wanted from us. Anyway, we are not really being tested on biology knowledge, but rather on our abilities to be in conformity with the logics of the test maker, aren’t we?
@Skarlo I’m pretty sure the answer to the plant fertilizer one was inorganic compounds, and I actually studied stuff about fertilizers in my biology and chemistry class.
The question was like “plant fertilizers provide which of the following that is essential to plant growth?” Fertilizers provide important elements for plants, among which most essential are nitrogen (N), phosphorus §, and potassium (K). These elements are absorbed by plants in the form of inorganic compounds. For example, N-fertilizers include (NH4)2SO4, NH4Cl, NH4HCO3 (not organic even though it contains carbon), etc; P-fertilizers include Ca(H2PO4)2, CaHPO4, etc; K-fertilizers include K2SO4, KCl, etc. (Although there are a few exceptions to this general rule. Urea CO(NH2)2, a Nitrogen-fertilizer, is organic.) Meanwhile, elements such as Ca, Mg, Na, which all come in the form of inorganic compounds, are also provided by plant fertilizers.
On the other hand, “nucleic acid” isn’t a perfect fit for this question. There are fractures in the logics of the choice “nucleic acid” because, although N and P are in the fertilizer and are used to synthesize nucleic acids, the fertilizer doesn’t directly provide nucleic acids for plants. Plants instead synthesize nucleic acids themselves. In fact, the chemical compositions of most of the fertilizers aren’t even organic. Moreover, K, Ca, Mg, Na aren’t used to synthesize nucleic acids, and therefore the choice “nucleic acids” is incorrect. Finally, although elements from fertilizers help in the production of nucleic acids, the effect of fertilizers isn’t limited within this range. For instance, N and P can also be used in protein production, and Mg is essential for chlorophylls. Choosing “nucleic acids”, therefore, means ignoring the assistance fertilizers provide for other biological processes in plants besides nucleic acid synthesis. Thus, the correct answer is inorganic compounds.
BTW, this question wasn’t stupid. I think it tested us on knowledge about the chemical nature of fertilizers and how the fertilizers actually support plant growth.
@Skarlo For the pine trees question, the answer choice “steeper slopes” is definitely incorrect. First, there wasn’t any information in the question itself that concerned steepness of slopes (Yes, I read the question several times and am 100% sure it didn’t mention or even imply about steepness), and of course TCB doesn’t expect us to know the difference in steepness between the north and south slopes (the question didn’t even mention the name of a particular mountain—different mountains have different geological appearances and certainly different steepness of slopes, which suggests the answer had nothing to do with steepness). Moreover, the question didn’t tell us anything about the pine trees’ tolerance of steepness. (Remember the critical reading section, if a piece of information isn’t stated or implied in the passage but appears in one of the answer choices, this choice is definitely incorrect.)
On the other hand, the answer choice saying “rainfall evaporates more rapidly on the south slope” makes perfect sense. The question implied that the mountain is in the northern hemisphere, and is more likely situated to the north of the tropic of Cancer (23°26’N). In geographical and astronomical terms, the regressive movement of the sun in the sky has a period of almost exactly one year. On the summer solstice (around June 22 every year), for any observer standing to the north of the tropic of Cancer, the sun reaches its highest point in the sky at noon. But for a mountain located to the north of the tropic of Cancer, sunshine can’t touch the north slope even on the summer solstice, and of course can’t touch the north slope on any other day of the entire year. In contrast, the south slope can be warmed up by sunshine on every day throughout the year (this is also the reason why the windows of houses generally open southwards instead of northwards). Because of such a difference in the distribution of sunlight between the two slopes, the south slope receives far more heat than the north slope does throughout the year (the infrared rays in sunlight cause thermal effect), which in turn explains the faster evaporation of precipitation on the south slope.
Meanwhile, although information about the pine trees’ tolerance of rainfall isn’t provided in the question, we are expected to know it. Pine trees belong to the phylum coniferophyta, and have needle-like leaves to make them more hardy in dry environments. As tall trees, they need to preserve water. So the greater amount of evaporation on the south slope seems inhospitable for pine trees. Shrubs, on the other hand, don’t necessarily confront this problem. Some hardy shrubs can even survive in deserts. Obviously, the lost of rainwater by evaporation doesn’t inflict as big a disruption on shrubs as it does on pine trees. Therefore, it is reasonable that pine trees grow on the north slope, while shrubs grow on the south slope.
There are 2 key elements in this answer choice: 1. Why does rainfall evaporate more rapidly on the south slope? (explained by the regressive annual movement of the sun). 2. Why can’t pine trees live on the south slope, where rainfall evaporates faster, while shrubs can? (explained by the difference in their biological features). Therefore, the answer for this question is “rainfall evaporates more rapidly on the south slope”.
The answer to the are these two species different question is compare DNA sequences. There is no doubt in my mind.
@CGlynn Why are you so sure? Could you explain why it is compare DNA sequences? I personally thought “Relocate some to a new marsh” made good sense though.
@AmericanGothic it is compare DNA sequences. It is the one that will most obviously indicate differences between the two species
@AmericanGothic right, I didn’t mean that 3 wrong CAN’T be an 800; I was clarifying that based on the CB practice rubric a 77/80 is an 800 but that doesn’t mean 3 wrong is 800.
what was the one for “how do you think a scientist will investigate the population density of a species in South Dakota?”
@AmericanGothic interbreeding doesn’t imply two organisms are the same species.
@College123college it’s the one that was like count the number and extrapolate
@normanxi Yeah I know, but interbreeding AND able to produce fertile offspring mean two populations are the same species, right? That’s the definition of “species”. I thought “Relocate” allows us to test if the two populations can interbreed and produce fertile offspring. But since so many of you said compare DNA sequences, I’ll count mine as wrong.
@RybkaShredder Well that makes sense. But the reason I didn’t say compare DNA is I thought it’s not very practical. If two populations are different species, how much difference should they have in their DNA sequences? Homo sapiens and some other primates have 98% or so of their genomes in common. Even if we compare DNA sequences of different human races, say blacks and whites, there’ll be some significant differences. So I think there should be a standard, or sort of a “threshold”— like 2% difference means two species, while 1% difference means the same species, etc. or something like this (you get my point). HOWEVER, I am not so sure what that standard will be, and even if we can find out the exact percentage of differences present in their DNA, are those differences significant enough to prove they are IN FACT two species? There is also a need to define how much difference can actually account for their being different species. In other words, the standard of judgment for speciation MUST be quantified if we choose to compare DNA sequences.
So with this in my mind, I returned to the basic definition of species: A species is a population whose members have the potential to interbreed in nature and produce viable, fertile offspring. I thought to prove they are different species by means of this definition is much easier than comparing DNA sequences. Thus “relocate” makes the best sense. Am I over-thinking or something? I now think I should have omitted this question… 8-X
@AmericanGothic You can’t assume things that the answer does not explicitly say.
AmericanGothic, you bring up the original definition of a species. It suggests a critical test of species-hood: two individuals belong to the same species if their gametes can unite with each other under natural conditions to produce fertile offspring. But this becomes complicated by the intricacies of reality. What about asexually reproducing organisms like bacteria? What about Horizontal Gene transfer (HGT), which occurs in prokaryotes AND eukaryotes? Also, what if the two species do not live near one another and cannot be observed under natural conditions? What if two individuals from different species mate and yet the hybrid offspring are still fertile, as is true of over 50% of all plant species?
The definition of a species is less confusing when we define the word using more generalized terms. A species can be thought of as a group of individuals that are similar not only in respect to their phenotypes, but also in their physiology, biochemistry and DNA sequences.
This is the general question: how to prove if two populations are two different species.
A-compare their behavior
B-compare their DNA sequences
C-compare their embryological development patterns
D-relocate some to a new marsh
E- ?
The best answer is B - compare their DNA sequences. Specifically, mitochondrial or chloroplastic DNA sequences are compared.
There are very specific reasons why this is the best method:
- It is the fastest method.
- DNA sequences are known for a great number of different organisms, allowing for the most comprehensive comparisons.
- Standards that define what constitutes enough DNA variation to identify different species vs. random genetic drift are already established.
- It potentially satisfies the most definitions of a species; the central dogma of molecular biology suggests that similarities at the DNA sequence level would result in similarities at the protein expression level, and thus affect a similar phenotype, biochemistry and physiology of two groups.
- It provides the most definitive and descriptive comparison vs. the comparisons provided by the other methodologies listed as answer choices.
The technique is described in detail in this PLOS ONE research paper - http://■■■■■■/07pX2S
What was the mitochondrial dna one?
@xxjmodxx it was like study origin of eukaryotes (endosymbiotic theory).
I picked one with the word evolution in it… Not compare dna. I hope that was the one you are referring to
@xxjmodxx yeah, it might have said the evolution of eukaryotes
@vmiller7723 wha t was the mitochondria question about? could you freshen me up a bit?
i think the mitochondrial question was about what the existence of double membranes and organelle dna in mitochondria and chloroplasts proves about the evolution of eukaryotes from archaea and prokaryotes, and it had to do with the endosymbiotic theory of evolution