You will notice that the page-numbers, headers, and “continued…” notations
have all been eliminated from this document, leaving just the substantive parts
of the exam. The instructions and questions are printed in the same font and
style as they were on the midterm paper, and numbered the same way.
The basic answer-scheme – those answers I had in mind before the exam
was written, with mark-breakdown expectation – is presented in italics;
any adjustments to the basic scheme, including additional acceptable answers,
part-mark assessments, and common mistakes or misunderstandings (with
explanations) are shown in colour. My extra comments are shown in blue, and the comments of my marker are shown in orange.
A summary of question-by-question results is provided at
the end of this document.
Please read and thoroughly digest this document before asking anything about your midterm.
If you notice any errors in addition, or in transfer of marks from answer-pages to the front cover, return the paper to WG with a brief note pointing out the problem.
If you wish to challenge any grading, remember:
U
re-evaluation of any question entails re-evaluation of the
entire exam (are you confident enough to risk losing marks on questions that
may have been graded too generously…?)
U
no exams written in pencil can be re-evaluated
Be sure to read and understand the “gateway” document through which you passed to reach this scheme-page…
if you ignore the advice therein, you may regret it.
§
Of course it’s the case that for some students, and for some questions,
time-limitation was the major problem. The resolution of this
will be in part a more rational workload that I assign on a final (no need to
fill all the time!), and in part your experience in practicing more questions
and getting feedback from this scheme and office-hour consultation.
§
Many students wasted time and space re-stating the question
in the answer-space – this is absolutely unnecessary, since the question
is right there! Launch straight into your answer… first thinking about it, of
course.
§
A substantial minority of answers used point-form inappropriately,
where a “full-sentences” explanatory argument was required. If the question
ever leaves you in doubt about the applicability of different forms of answer,
you should ask.
§
Many answers suffered from being too vague – get to the
point and argue specifically, use a single idea if the question requests one,
provide a definite mechanism rather than a general notion. Again experience
will help you do this better.
§
Another frequently-observed problem in grading was the confusing
and/or self-contradictory answer. Often I thought that you must know something,
but you undercut your own work by partial repetition, faulty re-phrasing, or
the inclusion of unconnected material, so it was difficult or nearly impossible
to evaluate your understanding. No doubt time was a factor here, but it is
important to develop the discipline of taking time to plan before you
write, it does pay off.
§
In many instances, it appeared that students did not take care to
read questions carefully enough. Writing answer-space material without
first being sure of what the question is asking is unwise, because it will
likely be off-topic and thus a waste of your valuable time. If you read but
didn’t understand the question, you should have asked for clarification.
§
When considering answering-strategy overall, many students could have
done better by applying a triage technique: divide questions
(without regard to question-length or mark-value) into (1) those you are
confident of answering immediately, (2) those you may be able to answer
with time and effort, and (3) those which you feel you probably cannot
address, and which are thus not worth spending any time on until you
have completed all of types (1) and (2). You may scare yourself at first by
doing this, but the time saved will be worth it, and you may find inspiration
on type-(3) questions as you work on the others.
1. Short questions. Answer all parts a - d. Allow up to 4 minutes
per part. Each part is worth 4 marks.
a) Our rainy weather in Vancouver is a result of air rich in moisture blowing in off the ocean, where evaporation had occurred (winds from the west are the norm). There are places on the Earth, however, where west winds blow off the ocean and the land area next door is very dry, not rainy (such as southern Peru, and Namibia, SW Africa). How can this be? Suggest and briefly explain one mechanism to account for this odd result. Click here to skip down to the mark-summary table.
A: since atmospheric moisture is
determined by the balance of what goes up and what comes down, the simplest
explanation is that “little comes down because little went up” – low
evaporation from the sea. This is worth 2 out of 4. If a reason for
it is given – very cold water, due to strong cold currents and/or upwelling of
deep cold water – then full marks. (This is in fact the main reason for both
locations mentioned.)
An alternative answer would be that “if the land were very flat, the wet air would not rise and condense to form rain (as it would along a mountainous coast)”… but this would not work for Peru, where it’s more mountainous than here! (Might work for Namibia, in part.) As long as the answer didn’t overgeneralize, it could still be near-full or full marks.
Probably the major problem in the answers you wrote was an
apparent misreading of the question. About half the papers simply referred to a
“rain-shadow” process, in which the dry area exists behind a barrier of
mountains whose west slopes receive much rainfall… but how could this possibly
give rise to a dry area “next door” to the sea? Clearly I thought it was not
a rain-shadow case, because in such a case the area next to the sea is wet
and not dry; the question was setting a contrast between what happens
here and what happens in other places. If there was at least a clear
explanation of the mechanism of a rain-shadow, I gave 1/4 (since it was such a common answer, and I
didn’t want to give zero after zero, even if it wasn’t the answer I wanted!).
Some students alternatively tried to use a Hadley-cell
explanation, dry air descending and blowing onto the land… but if the air is
dry, and it blows over the sea, it won’t be dry for long. In places where the
wind blows in another direction, this could be a good explanation, but
the question tells you explicitly that the wind is blowing off the sea.
If there was at least a clear explanation of the mechanism of a Hadley
cell’s action, I gave up to 2/4.
In a few cases the argument was given that the places
mentioned are close to the equator, and thus warm, so rising air stays warm and
no condensation occurs as the air crosses the land… but warm air off the sea
will hold a lot of moisture (unless the water is cold, see above), and the
atmosphere high up is cold even in the Tropics, so the only way I gave marks
for this was if the answer explicitly addressed the assumptions.
A few students came close to a good answer by saying that, for
some reason, the rain fell out of the air before reaching the coast; I gave
up to 2/4 for this, but no more because no
mechanism was given. One or two papers suggested that the rain might
condense and fall, but evaporate before reaching the ground (the technical term
for such “failed rain” is virga), and certainly part marks were given if
the mechanism was explained.
The answer could not be based on the requirements of
plants in the area! Dry-land plants cannot make the weather dry, the causation
is obviously the other way around.
b) Explain the purpose of replication in an ecological experiment. Click here to skip down to the mark-summary table.
A: if only one plot of each treatment-type (both
control and manipulations) were to be run, there would be fatal risks to the
success of the experiment (e.g. accidentally improper setup, faulty
measurements of what happens, confounding factor in a given plot, unanticipated
genetic or other variation among test organisms), and “one plot lost” means “no
data from a whole treatment”. If each treatment is run in multiple replicated
plots, these problems can be noticed and either eliminated from consideration
or at least averaged-over during analysis. It is worthwhile to do, even if it
may introduce “noise” because it’s hard to set identical starting-point
replicates.
The most common error in answering this question was
confusion of “replication” with “control”. Although both are involved with
making proper interpretations of the results, they are dealing with different
aspects of design. The control serves as a baseline-comparison for manipulated
treatments, and as a way of evaluating changing conditions outside the
experiment. Replication isn’t really for either of these.
A less common error was to mistake “replication” for
“repetition”; this is also less serious than the previous case, since
repeating an experiment provides validation more similar to the enhanced
validity provided by replication, but still an error because replication is
specifically within a single experiment – one ought not to be too surprised if
there are differences comparing one experiment to another, they are bound
to vary more than replicates in a single experiment.
A few papers presented “replication” as an attempt to make
conditions in an experiment like those in nature (“to replicate nature”), and
of course this may be desirable, but it isn’t the proper use of
the term. Several papers took the view that by “replication” I meant “copying”
(in the sense of DNA replication, or cloning), but since the question placed
the term explicitly in the realm of an ecological experiment, such answers were
puzzling.
c) A major cost to consumers of live animals is locomotion (running around to catch the mobile prey); species which consume dead items probably spend less on locomotion… but is this necessarily true? Suggest one scenario or situation in which eating dead items would still impose a high cost of locomotion for the consumer. Click here to skip down to the mark-summary table.
A: situational answer was the way to go. Option one,
start with a high-locomotion-cost species like a flying bird (vulture?) or
running mammal (hyaena?); any feeding-related locomotion for such an organism,
even if it moves slowly or over a short distance, involves substantial
respiratory-heat-loss cost! Option two, consider food-distribution in
space and/or time (scale); assuming that the consumer eats a specific
type of dead thing, and that the items are uncommon/widespread-apart/available
only from time to time, a lot of travel/searching would be needed, and this
would be costly for species of any physiology.
Overall this question was pretty well-answered, and indeed
there were several clever ideas given which fell outside the range I had
expected to see. The number of marks given always depended on the detail and
completeness of the specific answer, of course. Common answers not in my scheme
above included: consumers of dead items being obliged to move fast to escape
from their own predators when out foraging; consumers of desirable types of
dead items having to move fast to reach them before competitors;
consumers of dead items possibly having to engage in active chases or fights
with competitors at the feeding site; or consumers of dead items having to
push through a tough habitat to reach the items (e.g. digging or
swimming to reach them; these certainly can be categorized as high locomotory
costs). Any of these, clearly expressed, could be full marks.
Answers which mentioned “energy-cost” generally, and not
locomotory cost specifically, received at best part marks.
A rare but clever answer was to suggest that consumers not
specialized to eat dead items (just capable of doing so) might
expend a lot of energy attempting unsuccessfully to catch live items (which
they might likely prefer), and then be obliged to accept the less-preferred
option of dead things… in this case, even if collecting dead things was in
itself not costly, the overall foraging strategy imposed high locomotory
cost. Well-reasoned, for sure, and realistic in some cases at least; it was
clever because the question’s wording did not require the consumer to be
an obligatory eater of dead things, so a lateral-thinking answer was totally
appropriate.
d) In eastern North America, as European settlement proceeded across the continent, temperate forest was cut down and replaced with (grassland-like) agricultural fields… but temperate forest has about twice as much annual primary productivity as the cultivated land which replaced it. The claim has been made that it would have been “better” (more efficient) to have kept the forest, and harvested items from it, instead of replacing it with fields for agriculture. Do you agree or disagree with this claim? Select just one option, and explain your answer. Click here to skip down to the mark-summary table.
A: the easy one is to disagree: if we had been
harvesting for fibres/wood products alone, this may have been true, but food-harvesting
requires crops with a high and predictable yield of specific items (fruits,
seeds), and these would be difficult or impossible to collect efficiently from
the forest, even if there were enough present in the forest – most of the production
in the forest is wood and leaves, and not fruits or seeds! Agricultural crops
are more useful to humans, since a greater fraction of the productivity will be
edible even if the total produced is lower (less wood and thus more
digestibility in agriculture).
[The only way to agree might be to assume that food could have
been collected elsewhere or imported, at a lower cost than growing it locally
(questionable), and that keeping the forest would have enhanced wildlife
habitat for hunting deer as a source of high-quality food, and would have
sheltered human housing against winter conditions (so reducing energy-burning
pollution). The outcome might be “efficient”, but would not be consistent with
the way we live in North America!]
Some answers received
part-marks for useful but largely off-topic approaches, for instance: the
forest should have been kept because it was better adapted to the climate
and/or soil; the forest should have been kept because it would be more
stable and thus more easily managed; the forest should have been kept
because agricultural systems are often mismanaged (overfertilized, soil
blows away, too much pesticide) and thus damage the surroundings. Some
interesting answers observed that deforestation might lead to nutrient-losses,
so was dangerous, while others said that losses could be managed better in
well-monitored agricultural systems. All of these answers approached full marks
if they were explicit about the efficiency for human usage, and stated their
assumptions.
A few people said
that keeping the forest would be bad because it would take longer to regrow
after harvesting; this is true, but would you harvest a forest as intensively
as you harvest a wheat field? Sustainable forestry would involve more careful
use, mainly removing fruits and dead trees, so this argument had little force
to convince. If such an answer specified clear-cut forestry, it was more
satisfactory.
Poor answers included
the idea that clearing the forest would create more space for production (no
– the amount of area would be the same, whether in forest or agriculture), or
that it would be difficult to grow agricultural crops in the forest (true, but
the question explicitly says “instead”). A few answers merely agreed that there
was more productivity in the forest, and that this was a reason to maintain
the forest – hardly an explanation! Providing an account of why a forest
might have more productivity (e.g. better nutrient-recycling), even if
given correctly, was beside the point.
2. Medium questions. Answer both
parts a (page 3) & b (page 4). Allow up to 15 minutes per part (page).
Each part (page) is worth 12 marks.
a) [Answer all sections i - iii.] You observe two species of clover (call them species “A” and “B”) each making up about 50% the plant biomass on a pasture (meadow); assume that “A” and “B” individuals are about the same size, in biomass-per-plant, and that they have broadly similar growth requirements. State any other assumptions.
[i] Do the “50/50” data prove that the clover species are in a competitive coexistence? Explain your answer. (4 marks) Click here to skip down to the mark-summary table.
A: no, because you cannot
demonstrate the role of competition by mere observation, and in this case there
was no manipulation carried out to test it; alternatively, if you didn’t
explain this way but instead designed a suitable test (controlled removal
experiment), that was just as good an answer.
A yes answer cannot be correct, because of the
wording of the question (“prove”). If a “weak yes” were offered, something like
“if they weren’t in a coexistence state one would have driven the other out”,
then part-marks; if a “weak yes” said explicitly that “the observation
is at best consistent with coexistence”, then again part-marks.
When my marker had read 10 or so papers to get an idea of
how the question was being approached, she came up with the following
application of my basic scheme (can you tell that she learned some bitter
lessons as an undergrad from writing my exams herself?!):
0: You answered simply “yes” or provided no
clear yes/no answer at all. (Skirting the issue with complicated reasoning and
avoiding a clear yes or no is never going to get you many marks!)
1/4: You were on the
wrong track, but displayed accurate knowledge about the material. You may have suggested that the data
presented are consistent with coexistence; or alternatively that
if coexistence weren’t occurring, one species would have already/will
eventually push the other species out.
2/4: You were on the right track (so close!!) you
have clearly answered “NO” and you have also provided some examples of
more factors that may be at work here.
This is the format of most of the answers.
3/4: You were really on the right track, your
answer is probably just lacking some clarity.
(Remember: good
science is half assimilation of knowledge, and half clear and concise
communication of this knowledge; pay attention to the question, define what
points you need to cover in order to get full marks, and answer these points as
clearly as possible without running off on tangents…it is never necessary to fill
the entire space given to you with writing to get full marks.)
You may have
suggested, but not clearly stated, that more experimentation was
necessary by providing additional assumptions, thus making it clear that the
information given was not enough, without explicitly saying so. (“State your assumptions” DOES NOT
MEAN that you should reiterate the assumptions given to you in the
question. It is an opportunity for you
to strengthen your answer by making the question more specific…use this
opportunity!!)
4/4: Good work!!
You have clearly answered “NO”. You
have explicitly stated that mere observation is not enough to show
competitive coexistence, and/or that further experimentation is necessary.
[ii] On another pasture, which began like the one described above, the addition of fertilizer resulted in a shift from “50%A & 50%B” to “90%A & 10%B”. Propose and briefly explain one mechanism (hypothesis) to account for this change. (4 marks; answer this section independently of section [iii] below) Click here to skip down to the mark-summary table.
A: of course the obvious idea is that the resource(s)
added were much more conducive to the growth of one species than to the other…
but imposing extra complexity was not wrong, such as the idea that once
fertilized, species B becomes much more palatable to herbivores for some reason,
so A does better…. or that a large quantity of fertilizer had a “burning”
effect on B but less on A, because A has tougher tissues… or even a fact-based
idea, that clover has N-fixing bacteria on the roots, but the strain of
N-fixers on species B were for some reason more sensitive osmotically than
those on A and suffered from the fertilizing process. As long as the idea was
biologically plausible, I’d be happy.
The main marking emphasis was on a narrowly-stated hypothesis,
so for the first idea above: “the fertilizer contained a nutrient (or
combination) which strongly enhanced the growth of species A but only weakly
(if at all) that of species B”. A good idea only – one not couched in
hypothesis-terms – would be worth part-marks at most; a hypothesis-form
statement only – one not capturing a sound idea – would likewise get
part-marks at most.
Again, my marker took the basic scheme and fitted it to your
answer-styles:
0/4 = you offered no
biologically plausible idea nor hypothesis, you may have simply reiterated that
“species A did better than species B under these conditions”.
1/4 = you offered
a hypothesis statement that was not biologically plausible/reasonable, or was
plausible but largely incomplete (e.g.: species A did better with the
fertilizer than species B ; how/why??
There is no specific hypothesis here.)
2/4 = You provided
a weak/broad hypothesis with no substantial reasoning,… or some
reasoning without any explicit hypothesis,... or you clearly provided
both components, but these did not represent a biologically reasonable idea
about what plants might do, or were unsupported by assumptions.
3/4 = You were so
close!! You provided a significant
amount of reasoning for a plausible idea, but failed to follow directions and
provide the explicit narrow hypothesis statement,... or you presented a
clear, testable hypothesis, but with not quite enough reasoning.
4/4= You provided
a hypothesis statement that was concise, biologically plausible and testable - and
substantiated it with sound reasoning.
Half a mark was
deducted if the answer was otherwise “bang-on”, but used wishy-washy
non-affirmative language in the hypothesis statement, i.e.: “ …it is
possible that…” The hypothesis must state a definite claim about the role of a
factor, otherwise it cannot be critically evaluated (you can’t rule out a
“maybe”).
[iii] On another different pasture, which also began “50%A & 50%B” like the one described above, sheep (herbivores) live. Sheep strongly prefer to eat species A and dislike species B, but the plant-species balance is observed to remain at “50%A & 50%B”. Propose and briefly explain one mechanism (hypothesis) to account for this lack of change in plant-biomass pattern under herbivory. (4 marks; answer this section independently of section [ii] above) Click here to skip down to the mark-summary table.
A: it may have been tempting to say that species A must
grow way faster than B to keep up with the herbivory, but the plants are the
same species as in the main (no-sheep) case! So this cannot be right. However,
it would be quite reasonable to suggest that undisturbed A grows slowly, while
chopped-by-sheep A responds with vigorous growth. On the other hand, maybe A
makes good use of the nutrients in sheep waste to re-grow, but B for some
reason cannot. This would be reasonable assuming that the mineral nutrients in
A are largely still present in the waste of sheep who ate A, and are
preferentially picked up by A plants later.
This section was expected to be way harder than the others, so don’t be
surprised by poor results!
My marker had the following
application comments:
Basically the same
style of marking scheme as the application in [ii] above.
Some answers that
were not quite there, but that merited partial points:
§
Though
increased growth rate of A was not a valid point, increased growth rate for
a specific reason was given the opportunity for full points. This includes increased reproductive rate,
but had to say something specific like “A produces seeds at a faster rate and
can establish itself in available space faster than B” to merit full marks.
§
Suggestion of
another herbivore present in the system which was specifically fond of B. If it was set up properly with hypothesis, etc.,
it got some points, but I was reluctant to give it full points because it
wasn’t really getting to the point.
Some irritating
common mistakes:
§
SHEEPS is NOT
the plural form of SHEEP (yeesh…I’d say about 60% of the class made this
mistake. I’m not the best speller, but
this was bad). Similarly, FISHES is not a word (as in question 2a).
§
The
insinuation that “plant A will develop a defense in response to the
evolutionary pressure” is highly faulted. The question did not insinuate that
kind of timescale, and a lot of students seemed to suggest that the plants were
sentient and could therefore choose to develop defense mechanisms. If the situation at hand were indeed
occurring, then A would be wiped out long before evolutionary mechanisms could
exert their effects. Terms such as
“evolutionary race” “adapts faster” “senses it needs to adapt” “develops
traits” should be avoided at all costs!! (WG note – I had not expected any evolutionary
answers, though good ones would have been 100% acceptable… so it may not have
been wise to venture into that area without better understanding.)
§
It IS
possible that the pattern in which plant A and B grow is highly mixed and
difficult to separate, so that sheep have a difficult time eating just A and
cannot easily decimate the population, but it isn’t really a good explanation,
though inventive to say the least. (Sheep, like most herbivores, are very
selective in diet choice.)
§
Batesian
MIMICRY (not mockery, not millinery or what ever else people felt the need to
put) is not a valid process here.
b) [Answer both sections i and ii.] In shallow ocean water near a continental shore, currents stir sediment from the sea-floor up to the photic region near the surface, providing the raw material for the high-productivity phenomenon termed an “upwelling zone”. The abundant phytoplankton and zooplankton growing in such a zone can feed large populations of fish, attracting profitable commercial fishing fleets.
[i] The sediment contains a wide variety of organic and inorganic nutrients. Provide a brief experimental design which would allow fisheries researchers to determine what component(s) of the sediment is(are) most responsible for promoting productivity in the upwelling zone. (8 marks; state your assumptions) Click here to skip down to the mark-summary table.
A: so the first step would have to be identification
of all the components, so each could be tested under controlled conditions. (1
mark – I didn’t expect consideration of all the possible interaction
effects!)
Then each component in turn could be taken away experimentally,
probably easier to do in a lab where some fish could be held in tanks with
their normal prey-types (assuming they will all survive that way, and behave as
they would in the field), thus a set of component-absent treatments (1 mark),
to be compared with normal-seawater controls (1 mark), and then
evaluating fish growth-rate (and/or the success of the planktonic organisms) as
a suitable dependent variable (1 mark).
Allow 2 marks for some combination of suitable assumptions
and methodologies, including a mention of replicates.
Then the remaining 2 marks for predictions: in any
treatments where fish went downhill fast, or where they seemed to get a strong
check in growth, you would tag that (missing) nutrient as critical. If they
seemed to do just as well as controls, then that (missing) nutrient was
probably unimportant (not proven to be, of course). If plankton themselves were
monitored, then it would be possible to determine exactly where in the chain
the problem came in.
I expected many students to propose adding nutrient in this
experiment – not appropriate! The question asks which nutrients are
important by their presence, so manipulation should involve selective
removals.
If a design was good in other ways but suggested adding, then a maximum
of 6 marks was available. Similarly, if multiple hypotheses were presented rather
than one, only 6 marks were on the table.
My marker was rather
unimpressed with the overall standard of answers to this section, but tells me
that she is worried that she was too lenient in grading! Her detailed
approach (I inserted design-component notes in blue to organize it):
This is a question
about scientific design. Period. Good
ideas are good ideas, but you need to be comfortable with placing such ideas
appropriately in the scientific process in order to get anywhere with this
question. Clear definite hypothesis statements, not wishy-washy “may”
statements, are essential.
If an unfeasible
or unclear hypothesis was suggested, this was marked independently as a
constant error, and the student still had the opportunity to gain points for
appropriate methodology etc., that is, marks were not removed
twice.
If multiple hypothesis or suggestions were made, I picked the most complete one and graded that (to a maximum of 6 marks as suggested). It is important for students to remember that though they will not lose marks for bad information, it does not benefit them to bog the marker down in a confusing maze of reasoning. One bad idea, which is fully realized in a design, is bound to get more marks than several pretty-good ideas presented in an incomplete/mixed-up format.
(treatments/methodology) While some people did suggest adding components as their experimental manipulation, even more suggested testing only one component at a time…that was hard to mark! I usually let it slide if they suggested isolating the environment (in a lab) and only adding one nutrient. I didn’t accept it if they said they just picked a plot and added one more nutrient each time. Almost no one remembered to have replicates.
(methodology) A
lot of people seemed to think the point of the question was to determine if it
was the organic or inorganic nutrients in the sediment which were
influential (i.e. two choices only).
I graded this fairly easily as I felt it was a reasonable
misinterpretation.
(dependent variable) I allowed imprecise measurements such as “which one
thrives more, which one grows more” as an appropriate measurement only because
it was your first exam. In future, any answers lacking a specific measure such
as “measuring biomass by weight of the fish/plankton” just won’t do – vagueries
like “measure the growth of that area” or “measure the productivity” are
grossly incomplete statements and will not be acceptable. In fact it seems like
the term “productivity” in the question really bogged students down, rather
than pointing toward an appropriate measure. Actually almost no one explicitly
stated what was being measured.
It would often be mentioned incidentally in the predictions or stated
otherwise: “if A is more important, the productivity of the tank I added it to
would go up.”
(predictions) This
is another area in which affirmative, definite language is necessary. Not “if A is important, B will change”, but
rather “ I predict that an increase in A will result in a decrease of B.” I
deducted one point for wishy-washy predictions like the former. As was the case
for a dependent variable, almost no one provided explicit predictions!
So overall grading
summary:
1 mark:
identification of testable components, or provision of alternate hypothesis.
1 mark: for the
identification of the independent/dependent variables (I also accepted any
statement of what was going to be altered/measured as an assertion of the
independent/dependent variables present.)
1 mark: for what
you are going to do with the identified independent variable.
1 mark: in what
environment are you going to do this manipulation (tank? the sea?)
1 mark: for
controls.
1 mark: for
replicates.
2 marks: for
predictions.
Now for my ease of
grading, and for students’ information, I marked what was missing for the
question in my own shorthand, as follows:
I = missing the identification of the
component(s) to be tested. (1 mark off)
M = what are you measuring? (1 mark off)
Δ = what are you changing? (1 mark off)
E = where/how are you setting up the
experimental environment? (1 mark off)
C = missing controls. (1 mark off)
R = missing replicates. (1 mark off)
P = missing predictions or assumptions (1 or 2 marks off, depending on how much was
missing)
Add = if you said to add
nutrients/components rather than take them away (1 mark off)
[ii] Imagine for this section that an experiment like the one you suggested in section [i] above were carried out, and a couple of critically-important nutrients were identified. How could you make practical use of such results to further enhance the economic returns from fishing (i.e. increase the production of fish) in the zone? (4 marks; hint – remember that practical actions may carry unintended/negative consequences, so don’t destroy by accident!) Click here to skip down to the mark-summary table.
A: the main idea here was to propose addition
(enrichment) to promote growth of fish-feeding, that is, a “specific
fertilization” approach involving those sediment-components said to have an
impact on the fishery. Such an answer by itself would be only part-marks
because the question telegraphs it. An answer suggesting moderate
addition (and pointing out some danger from heavier additions) would be
superior, depending on detail. An answer which also took into account
possible food-competition from other species out there, and/or enhancement of
the predators of food fish species (and thus no enhancement of the desired food
fish) would be worth even more. Answers in which possible toxicity of the added
materials, or possible disruption to community structure from changing the
nutrient pattern, was also considered, as a counterweight to the
potential benefits, would certainly be full marks.
So I counted
specific points you could have suggested, adding them towards full marks (each
point = one mark):
§
Suggest a
moderate/controlled/closely-monitored addition
§
Take into
account the effect on other species, or how the addition may affect
competition/coexistence relationships/community structure.
§
Suggest how
the addition may affect predation; make sure that subsequent predation doesn’t
nullify your growth effects due to the addition
§
Suggest
possible toxicity of the added material, or unplanned over-enrichment of other
species, etc…
On the other hand,
stating something like: “however, there may be certain negative consequences”
could not gain you marks; it was already stated within the
question. You needed to suggest what
those consequences could be (as in the points above). Similarly, if you said
something like: “further testing would be necessary”, no marks were given,
because the question really wasn’t asking this…it was asking you to “make
practical use” of the results increase fishing yields.
I might also add to
this that the marker thought I was asking a bit too much of you in 2a)[ii],
even allowing for the presence of the hint, but she applied a consistent
approach to grading in any case.
|
Topic |
Average mark |
Average as % |
Range |
Failure rate (%) |
|
|
|
|
|
|
|
|
|
1a) |
Dry land by the sea |
1.03/4 |
25.7 |
0-4/4 |
76.4 |
|
1b) |
Replication in experiments |
1.80/4 |
44.9 |
0-4/4 |
44.6 |
|
1c) |
Dead food, high cost |
3.08/4 |
77.0 |
0-4/4 |
14.6 |
|
1d) |
Harvesting the forest |
2.70/4 |
67.6 |
0-4/4 |
24.6 |
|
(Ques.
1 total) |
--- |
(8.57/16) |
(53.6) |
(0-15/16) |
(33.2) |
|
2a) [i] |
Clover in competition? |
5.78/12 |
48.2 |
0-11.5/12 |
47.7 |
|
2a) [ii] |
Fertilizer and clover |
||||
|
2a) [iii] |
Sheep and clover |
||||
|
2b) [i] |
Upwelling factor(s) expt. |
4.90/12 |
40.9 |
0-10/12 |
57.3 |
|
2b)
[ii] |
Enhancing upwelling zone |
||||
|
|
|
|
|
|
|
Exam Total |
--- |
19.20/40 |
48.0 |
3-33/40 |
49.6 |
When evaluating your performance on the midterm, try to remember what makes an appropriate comparison: you should not be thinking of marks you may have earned in typical high-school quizzes!
§ Did you do poorly overall, as compared to the class average? (worrisome)
§ Did you fail only those components with a high failure-rate? (not so bad)
§ Did you do poorly mainly where you ran out of time? (not so bad)
§ Did you have at least some components above class-average values? (good)
§ Did you have at least one page above class-average values? (better)
Remember that practice will
make a big difference in most students’ exam-writing abilities.
Recall also that, at the end
of the term when all marks are in hand, I reserve the right to make
“across-the-board” adjustments to grades in order to achieve reasonable average
and failure-rate results (for example, to make them similar to those in other
sections).