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Critical thinking
Alison Campbell
Dept. Biological Sciences
Scholarship criteria
The student will use biological knowledge and skills to
analyse biological situations and integrate ideas into a
coherent response.
For “outstanding performance”, the student will
demonstrate perception and insight in the analysis and
integration.
(Biology Scholarship standard, Ministry of Education)
Scholarship students are expected to demonstrate high
level critical thinking, abstraction and generalisation, and
to integrate, synthesise and apply knowledge, skills,
understanding and ideas to complex situations.
(Scholarship Performance Reference Group)
Question 3, 2004
Scholarship Biology
The three examples shown represent just some of the
diversity found in bony fish.
Use the diversity of the fish and/or any other named
group(s) to discuss the following statement:
‘Diversity is the end product of evolution.’
Candidates who did not achieve the standard tended to
describe rather than discuss in Question 3, and while
there were a lot of descriptions of the diversity in fish,
there was little or no attempt made to discuss the
evolutionary processes that resulted in this diversity.
Candidates gave their own opinion as an evaluation.
Overall:
Successful candidates addressed the question asked,
with minimal irrelevant material presented. Answers
were coherent with ideas integrated, and it was clear
these candidates spent time planning their answers
and organising their ideas.
Unsuccessful candidates wrote in generalisations
rather than specifics e.g. “it evolved by natural
selection”. They tended to use inappropriate
descriptors e.g. “catastrophic”, “terrible”, rather than
biological terms.
Critical thinking means seeking reliable knowledge.
Many students fail to assess the reliability of
information to which they are exposed in everyday life,
let alone pursue the dissection of scientific literature.
And many people are deceived and defrauded by
pseudoscience. Practice in critical thinking prompts
thoughtful examination of the role of science in society.
Wind farms & bird kills
Wind farms & bird kills:
In the United States (where some of the earliest wind
farms were poorly sited in areas where there were lots of
bird movements), a study shows that between 10,000 and
40,000 birds are killed by turbines each year.
This seems like a lot – and a good reason to reconsider
the use of wind farms…
However, you need to consider the other causes of bird
deaths. In the US:
• cars & trucks kill 60 – 80 million birds per year;
• buildings/windows kill 98 – 980 million per year;
• communication towers kill 4 – 50 million per year;
• the biggest killers of birds are domestic & wild cats, which
are estimated to kill up to a billion birds every year.
Environmental scientists in NZ say that as long as care is
taken about where we site wind farms, they present only a
very small danger to birds & bats.
Food allergies,
vitamins, &
overgeneralisations
Many people can’t drink milk, due to an allergy
or intolerance. However, milk contains a lot of
nutrients - & so the r.d.a. is 2 servings/day for
an adult.
Still, for some people it’s quite harmful – if they
can’t tolerate milk (or any food) they shouldn’t
eat it just because it’s in the “healthy foods”
pyramid!
In other words, evaluate by the principle of
individuality: by your own uniqueness.
However, someone may become quite sick
after a glass of milk. Instead of properly
evaluating the situation and saying "I should
not drink milk," they instead overgeneralise
and say "Milk is bad ... no one should drink
milk."
This is overgeneralising from personal
preferences. The principle of individuality will
help to counteract this tendency to evaluate a
person, or group of persons, or a food, as
being all bad or all good and then projecting
our expectations onto all our encounters with
this person or food.
Or look at Vitamin A: it’s a "vitamin" & so it
must be good for us! This is a common
perception.
However, Vitamin A can be lethal. The
recommended daily dose of Vitamin A is
around 1,000 Retinol Equivalents each
day:
• Ingesting 5 REs a day will eventually
lead to death from Vitamin A deficiency.
• Taking in 100,000 REs a day will lead to
hypervitaminosis A … & eventual death.
Many people have made themselves
sick and even killed themselves by
disregarding the individuality of dose.
A little may be good for you, but a lot
may kill you. Even plain water can kill
you if you drink too much.
Saccharin & cancer
Saccharin is a non-calorie sweetener widely used in
foods since World War I. Up until the 1970s many
diabetics & weight watchers used saccharin as a
sugar substitute.
A 1977 study of rats found that saccharin could
cause cancer. The FDA banned saccharin from the
food supply, & though this has since been reversed
many people remain fearful of saccharin.
BUT:
• Saccharin has been found to cause cancer only in one
species – rats. It does not affect many other species, such as
monkeys, mice and guinea pigs.
• Among rats, saccharin caused an increased incidence of
bladder cancer in male rats, but not in female rats.
• Yet the media focussed on labelling saccharin a "carcinogen"
without reference to species, as if a carcinogen in rats will
automatically be a carcinogen in humans.
• By 1990, 392 chemicals had been tested for carcinogenicity
in both mice and rats.
• 226 were found to cause cancer in at least one species;
however 42% of these carcinogens caused cancer in ONLY
one of these species!
There is clearly significant variability between species in
cancer risks. If nearly half the known rodent carcinogens can't
be generalized from one rodent species to another, how can
we confidently generalize from male rats to humans?
The media also tend to overgeneralise between reporting of
"carcinogens" and the way we test chemicals for
carcinogenicity.
The rats in the saccharin experiment received the equivalent of
someone drinking 800 cans of diet coke every day! This high
dose was selected so that relatively few animals could be
used.
BUT a substance may have different effects at different doses.
No human would drink anywhere near that amount of
saccharin in one day, let alone each day for their entire life!
However, the media reported the study as if the dose were
irrelevant.
In fact, several essential nutrients in humans, including
selenium and retinol (a form of Vitamin A), cause cancer when
fed in high doses to some animal species. If we applied
saccharin standards to these essential nutrients they would
have to be banned from the human food supply.
In 1989 came the announcement that dioxin had been found
in milk served from paper cartons. The dioxin had leached
from the paper cartons into the milk.
Newspaper stories of the dioxin-tainted milk invariably
referred to dioxin as a carcinogen, implying that increased
incidence of cancer would await the children exposed to the
tainted milk.
However:
• Dioxin had been found to be a carcinogen
in some animal species, but not in others.
• And it had been found to decrease the risk
of some types of cancers in some species.
Dioxin, in other words, could just as
truthfully be called an anticarcinogen.
A second media over-generalisation
involved the amount of dioxin in milk:
• Most milk samples tested revealed no
detectable dioxin, but the highest amount
of dioxin in a tainted sample was
measured at 0.07 parts per trillion (ppt).
• 0.07 ppt is equal to 70 nanograms of
dioxin in 1200 litres of milk.
Rats & the safety of GM diets
In a 1998 experiment, rats were fed GM
potatoes: the potatoes contained a gene from
snowdrops that expressed the protein lectin.
Lectin can act as a natural pesticide.
The researchers fed groups of rats one of these
menus:
• lectin-boosted modified potatoes,
• unmodified potatoes,
• or unmodified potatoes plus lectin from a
bottle.
What the study found:
• Eating potatoes with lectin (in any form) was
associated with a thickening of the mucus
membrane lining the stomach.
• In rats that ate only raw genetically modified
potato, the mucus-producing pits of the small
intestine were longer, compared to other rats in
the study.
• Rats eating transgenic potatoes had fewer
lymphocytes compared to those eating normal
potatoes.
The scientists’ conclusions:
• Eating potatoes modified to produce lectin caused some
cells to grow, and others to fail to grow, in the stomach and
intestine.
• At least some of these effects were due to the foreign gene.
Other effects could be due to the process of genetic
engineering itself.
• The genetic modification process could cause similar
outcomes when used to move other genes.
Rats & GE diets – what was wrong with this study?
• Too few rats – only six per food type – were used.
• Poor diets: all the rats ate pure potatoes, which contain
only 6% protein (normal lab rats get 15%). "There is
convincing evidence that short-term protein stress and
starvation impair the growth rate, development, hepatic
[liver] metabolism and immune function of rats."
• There was no control group – no group of rats ate a
good rat diet for comparison.
• Critics maintain that “no consistent patterns of changes
were observed” during the study.
Food irradiation
1. Discuss techniques that scientists could use to detect
DNA damage in microbes. What key factors would
have to be considered? Use diagrams if necessary.
This question is testing the application of certain
genetic and other techniques and the ability to
consider key factors in designing experiments.
This tests some of the skills of practical
investigation.
2. The safety of food irradiation is a controversial issue in
New Zealand at the moment. There is not enough
information given above to fully evaluate this issue. What
questions would you ask of scientific experts and what
information would gather before you could make an
informed choice as to whether food should be irradiated?
This is testing the skills of evaluating issues. The
first thing to work out here is the key issues
highlighted earlier. Notice that you are asking
questions, not necessarily answering them. The
ability to know the questions to ask is a really
important skill. Also, this is a science paper, so you
will be wanting hard data!
Consider these questions under the following headings:
(i) The effectiveness and safety of gamma rays.
This question is about gamma rays. So
immediately recall your knowledge about the
penetration of gamma rays. Think about how the
radiation source is used and how it is stored.
(ii) Consideration of the relative risks involved in
irradiating food.
This is testing the skills of writing a case study. Go
through the passage carefully and consider the
arguments for either side of this debate. Also consider
relative risks, e.g. methyl bromide can be used for
destroying exotic pests but it harms the ozone layer.
So is radiation a better option here?
Consider things like the incidence of food borne
diseases – one question you may want to ask experts
or find out more information about is how serious a
problem this is.
What else may you want to find out about?
Osteichthyes:
http://ipimar-iniap.ipimar.pt/DITVPP/site/introducao/fish.htm
Seahorse:
http://www.afcd.gov.hk/conservation/images/cop12/Seahorse%203.jpg
Anglerfish:
http://earthguide.ucsd.edu/hughes2001/acct/bmounmanivong/lifethatglows/angl
erfish.htm
Tararua wind farm:
http://www.ourregion.co.nz/gImage.php?gImageID=571&gallery=4&regionID
Irradiation cartoon:
http://www.msu.edu/user/sawyerc/outline-1-wilson.htm