I'm polishing up some of the material I'll present in classes #4 and #5 of my intro biology course. I think class #4 is OK. It introduces DNA, chromosomes and genes, although 'introduces' is hardly the right term for something the students will have been learning about about since grade school. In this class chromosomes are just DNA molecules big enough that they have lots of genes, and different chromosomes have different sequences and different genes. But it gets a lot more complicated in class #5.
Class #5 is about how DNA and genes and chromosomes vary. It first introduces the evolutionary concept of homology - defined as similarity because of descent from a common ancestor. Then we take the previous class's introduction to chromosomes etc. and consider the relationship between our paternal and maternal sets of chromosomes, and why we refer to them as 'homologous'. I push the idea of these being different versions of the same chromosome, but students often find the whole business confusing, which puts them in deep trouble when we move on to meiosis and genetic analysis.
Part of the confusion arises because chromosomes are physical things but they are also conceptual categories of things. Two particular DNA molecules in a particular cell in your body (e.g. in the skin cell closest to the tip of your left index finger) are chromosome 13s, but we can also refer to 'your maternal chromosome 13' (of which there are as many as there are cells in your body, about 10^10) and to 'human chromosome 13' (2 x ~10^10 x ~7x10^9). And these are far from identical.
Students need to think about the differences between the versions of human chromosome 13, as well as what unites them, and this isn't easy. This point in the class will be a good place (one of many) to emphasize the importance of variation in biology. For first-year students, having to think about variation and diversity will be new, and it's one of the big things that separates biology from the physical sciences (see Why biology is harder than physics).
Maybe I can give them a sketch that moves out from the single cell to the human population. Let's see what I can pull together from Google Images.
Sunday, January 06, 2008
HapMap for beginners?
This year I'm going to use the human polymorphism map (the HapMap) as part of the framework for thinking about genetics and evolution in my first-year biology course. I haven't done this at all before, but I can see a lot of places where it would fit naturally. Most of the other instructors in this course seem to be content to teach the standard Mendelian genetics, but I think students need to learn about the modern resources and issues that the popular media will expose them to.
Classes start tomorrow, but we won't get into the HapMap until next week, when we start talking about DNA and genes and genomes and chromosomes. Monday these will be introduced, and Wednesday we'll consider how they vary. Then on Friday we'll consider how human variation corresponds (or doesn't) to conventional views about human races.
In some ways using the HapMap will mean moving the level of understanding up a notch, but in other ways it may help students make sense of what their genes and chromosomes are.
Classes start tomorrow, but we won't get into the HapMap until next week, when we start talking about DNA and genes and genomes and chromosomes. Monday these will be introduced, and Wednesday we'll consider how they vary. Then on Friday we'll consider how human variation corresponds (or doesn't) to conventional views about human races.
In some ways using the HapMap will mean moving the level of understanding up a notch, but in other ways it may help students make sense of what their genes and chromosomes are.
Friday, January 04, 2008
My recent provocative post on Why biology is harder than physics has been discussed by both Philip Johnson on Biocurious (critically) and Larry Moran on The Sandwalk. (favourably). One commentor on my post, Fred Ross, then complained that I was misusing the term 'complex'.
One context where such words create big problems is for students learning science. In biology we have words like adapt, assort, base, segregate, phase, message, membrane, sex. Two colleagues even wrote a whole article about many meanings of the one word 'cross' ("The crosses genetics students have to bear"). The teaching fellow associates with my Biology 121 course has been compiling a list of such words, and I'm going to ask my students to start collecting them for their own learning.
But I've also started putting out feelers about such words to linguists and educators, wondering if they have insights into how our brains (and our students' brains) deal with such words. I'm even wondering if we might get together a workshop of researchers in different disciplines to try to clarify the issues they raise.
It's also a pet peeve of mine that biologists insist on calling their organisms "complex," a very specific, technical term which I have never seen justified in biology. They are complicated, but I have seen no evidence that they are complex. There are problems of graph theory that are complex, but the graphs that biologists insist on writing down of protein interaction and genetic networks aren't sufficiently well posed to take any difficult mathematical problem that appears in them seriously.This is a timely point as I've been thinking quite a lot lately about words that, like 'complex', have both an everyday meaning and one or more specialized meanings. Evolutionary biologists have been fumbling with this problem as it arises for the word 'theory'. When we speak of 'the theory of evolution' we are using the work in a very special philosophy-of-science sense, but creationists then criticize evolution as being 'just a theory', using the term in its everyday sense and counting on the general public not knowing the difference.
One context where such words create big problems is for students learning science. In biology we have words like adapt, assort, base, segregate, phase, message, membrane, sex. Two colleagues even wrote a whole article about many meanings of the one word 'cross' ("The crosses genetics students have to bear"). The teaching fellow associates with my Biology 121 course has been compiling a list of such words, and I'm going to ask my students to start collecting them for their own learning.
But I've also started putting out feelers about such words to linguists and educators, wondering if they have insights into how our brains (and our students' brains) deal with such words. I'm even wondering if we might get together a workshop of researchers in different disciplines to try to clarify the issues they raise.
Monday, December 31, 2007
How to teach Hardy-Weinberg equilibrium
Over on the Gene Expression blog there's a discussion about how to explain Hardy-Weinberg equilibrium. Commentors are claiming that it's best explained mathematically rather than verbally. I'm posting a comment arguing that the best explanation is pictorial. Because I don't think I can put the picture in the comment I'm putting it here.
And here's the text of the comment I posted:
The best way to describe (and teach) Hardy-Weinberg Equilibrium is neither mathematically nor verbally but graphically, using a drawing that's like a Punnett Square with allele frequencies replacing the alleles. I've posted an example on my teaching blog.
Viewed this way, HWE is so obvious and so intuitive that there's no need for ps and qs at all. (And there never was any need for the apparent complication of q, as it's just 1-p.) The sides of the square are simply labeled with the actual allele frequencies, and the areas they create are the genotype frequencies in the next generation.
Of course math will be needed to deal with the deviations from HWE produced by selection and other factors, but starting with this graphical explanation helps beginning students see how simple and inevitable HWE is. (My freshman class on this is titled "The incredible tedium of Hardy-Weinberg equilibrium".)
Wednesday, December 26, 2007
Why biology is harder than physics
Beginning university students in the sciences usually consider biology to be much easier than physics or chemistry. From their experience in high school, physics has math and formulae that must be understood to be applied correctly, but the study of biology relies mainly on memorization. But in reality biology is much more complex than the physical sciences, and understanding it requires more, not less, brain work.
Biological processes of course are consequences of physics and chemistry, which is why we require our biology students to study the physical sciences. But organisms are also historical entities, and that's where the complexities arise. The facts of physics and chemistry are constant across time and space. Any one carbon atom is the same as any other, and today's carbon atoms are the same as those of a billion years ago. But each organism is different. That's not just a statement that fruit flies are different from house flies. Rather, each fruit fly is different from every other fruit fly alive today, and from every other fruit fly that ever lived, and it's the differences that make biology both thrilling and hard.
The differences have several causes and consequences. One cause is that biology depends on past history, because descendants are not identical to their ancestors. This is true at all scales, and the fundamental reason is that the process of genetic inheritance is not perfect. The DNA sequences we inherit from our parents are never identical copies of their DNA - instead they contain copying errors. So every copy is slightly different, even between two siblings. We are all mutants. These differences also accumulate over the generations, like in the party game Americans call "telephone" and the British call "Chinese whispers".
The second cause is natural selection, which shapes the accumulation of differences, favouring those that improve survival and reproduction and making it harder for disadvantageous differences to persist over the generations. And because most natural selection arises from interactions with other evolving organisms rather than with the relatively stable physical environment, the changes are rapid.
The result is that all biological systems are diverse at all levels. Even high school students are used to the idea of 'biodiversity', meaning the dramatic differences between different species of plants and animals. But the diversity is much more ubiquitous. Within each multicellular species, every individual is genetically different; every fruit fly is genetically different from every other fruit fly. The invisible bacteria turn out to be much more diverse than anyone would have thought. Bacteria isolated from natural environments are so different that even the individuals we would have considered the same species turn out to have about 10% of their genes from unrelated sources. In lab cultures, bacterial mutation rates are high enough that a single ml of culture will contain millions of different genotypes.
Even genetically identical cells are not functionally identical. When a cell divides its molecules are randomly distributed between the two daughters; because 'randomly' does not mean 'evenly', these daughters will have inherited different sets of the proteins and RNAs that carry out their functions. And even if the two cells had identical contents, these contents would still have different interactions - repressors bump into cofactors at different times, DNA polymerase slips or doesn't slip at different points in its progress along a chromosome. Understanding the how and why of biological phenomena thus requires us to consider historical and ecological factors that are many orders of magnitude more complex than those of physical systems.
The critical word is probably 'population'. Biologists rarely try to define it, but they use the term everywhere to refer to similar but not identical organisms or cells (or even molecules) that interact in some way. 'Population thinking', the realization that species are populations, not pure types, is said to have been key to Darwin's insight that members of a species undergo natural selection. And population thinking is probably what makes biology so much more complex than the physical sciences.
Of course we can't consider all of the differences all of the time, so at different levels of study we biologists try to pull out the factors that we think will matter most. Molecular and cell biologists work with populations of molecules, but they keep everything else as identical as possible. Developmental biologists study how cells become different, but they use pure-breeding lines and clones to ensure that the genetic properties of their organisms are as identical as possible. Ecologists pay attention to the big differences between species, but under conditions where they can ignore the differences between the individuals of each species.
I don't think population thinking is addressed in high school biology. We can't really blame their teachers, because the issues probably were never made clear to them either. Instead high school teachers pass on the facts they remember from what they themselves learned at university. The result is that their students enter university expecting their biology education to consist mainly of memorizing lots of new facts.
We instructors want our new students to start focusing on understanding complex processes and interactions, between entities that are themselves populations of diverse and somewhat unpredictable entities. We're thus asking them to set aside all the learning strategies that worked well for them in high school biology, and to learn in a new way. To students this probably seems the height of foolishness, and they're understandably reluctant to take the chance. So one big challenge, for instructors and for our students, is to find ways to ease this transition. We need to give students confidence that deep understanding will bring better grades than will rote memorization, and that saying "What I don't understand is..." is not an admission of failure but the essential first step to this understanding.
Biological processes of course are consequences of physics and chemistry, which is why we require our biology students to study the physical sciences. But organisms are also historical entities, and that's where the complexities arise. The facts of physics and chemistry are constant across time and space. Any one carbon atom is the same as any other, and today's carbon atoms are the same as those of a billion years ago. But each organism is different. That's not just a statement that fruit flies are different from house flies. Rather, each fruit fly is different from every other fruit fly alive today, and from every other fruit fly that ever lived, and it's the differences that make biology both thrilling and hard.
The differences have several causes and consequences. One cause is that biology depends on past history, because descendants are not identical to their ancestors. This is true at all scales, and the fundamental reason is that the process of genetic inheritance is not perfect. The DNA sequences we inherit from our parents are never identical copies of their DNA - instead they contain copying errors. So every copy is slightly different, even between two siblings. We are all mutants. These differences also accumulate over the generations, like in the party game Americans call "telephone" and the British call "Chinese whispers".
The second cause is natural selection, which shapes the accumulation of differences, favouring those that improve survival and reproduction and making it harder for disadvantageous differences to persist over the generations. And because most natural selection arises from interactions with other evolving organisms rather than with the relatively stable physical environment, the changes are rapid.
The result is that all biological systems are diverse at all levels. Even high school students are used to the idea of 'biodiversity', meaning the dramatic differences between different species of plants and animals. But the diversity is much more ubiquitous. Within each multicellular species, every individual is genetically different; every fruit fly is genetically different from every other fruit fly. The invisible bacteria turn out to be much more diverse than anyone would have thought. Bacteria isolated from natural environments are so different that even the individuals we would have considered the same species turn out to have about 10% of their genes from unrelated sources. In lab cultures, bacterial mutation rates are high enough that a single ml of culture will contain millions of different genotypes.
Even genetically identical cells are not functionally identical. When a cell divides its molecules are randomly distributed between the two daughters; because 'randomly' does not mean 'evenly', these daughters will have inherited different sets of the proteins and RNAs that carry out their functions. And even if the two cells had identical contents, these contents would still have different interactions - repressors bump into cofactors at different times, DNA polymerase slips or doesn't slip at different points in its progress along a chromosome. Understanding the how and why of biological phenomena thus requires us to consider historical and ecological factors that are many orders of magnitude more complex than those of physical systems.
The critical word is probably 'population'. Biologists rarely try to define it, but they use the term everywhere to refer to similar but not identical organisms or cells (or even molecules) that interact in some way. 'Population thinking', the realization that species are populations, not pure types, is said to have been key to Darwin's insight that members of a species undergo natural selection. And population thinking is probably what makes biology so much more complex than the physical sciences.
Of course we can't consider all of the differences all of the time, so at different levels of study we biologists try to pull out the factors that we think will matter most. Molecular and cell biologists work with populations of molecules, but they keep everything else as identical as possible. Developmental biologists study how cells become different, but they use pure-breeding lines and clones to ensure that the genetic properties of their organisms are as identical as possible. Ecologists pay attention to the big differences between species, but under conditions where they can ignore the differences between the individuals of each species.
I don't think population thinking is addressed in high school biology. We can't really blame their teachers, because the issues probably were never made clear to them either. Instead high school teachers pass on the facts they remember from what they themselves learned at university. The result is that their students enter university expecting their biology education to consist mainly of memorizing lots of new facts.
We instructors want our new students to start focusing on understanding complex processes and interactions, between entities that are themselves populations of diverse and somewhat unpredictable entities. We're thus asking them to set aside all the learning strategies that worked well for them in high school biology, and to learn in a new way. To students this probably seems the height of foolishness, and they're understandably reluctant to take the chance. So one big challenge, for instructors and for our students, is to find ways to ease this transition. We need to give students confidence that deep understanding will bring better grades than will rote memorization, and that saying "What I don't understand is..." is not an admission of failure but the essential first step to this understanding.
Monday, November 12, 2007
Can we do a Genetics reading assignment?
The New York Times is publishing a series of very good articles (11 so far) under the heading The DNA Age, about the social and personal implications of DNA sequencing. I'd like to find a way to require all of my BIOL 121 students read and think about at least one of these articles.
How could this work? I'd tell them they need to choose one of the articles to read, and that they will be asked to write a paragraph about what they've read, in response to an article-specific question I'll post. They'll be encouraged to discuss their chosen article with other students, face to face or on the WebCT discussion board, but will need to compose their own paragraph answers. To discourage copying I can have them submit their paragraphs to Turnitin as well as in answer to a WebCT quiz question. I don't know yet what kind of questions I'd ask them.
Marking this would require some extra grader hours - I'd give them a strict word limit for their answers but even marking 400+ 50-word paragraphs will be a big chore. More generally, I'd like to shift at least 5% and maybe 10% of the course mark from the midterm and final to in-class and homework activities. I guess it's time I read up on ways to incorporate peer evaluation into such activities and assignments. I'm getting hold of a book by Eric Mazur called "Peer Evaluation"; I hope this will help me shift much of the marking burden onto the students (who will learn an enormous amount by doing it).
I think peer-marking is one of the things that our new WebCT-Vista system is supposed to facilitate. I hope it's not too hard to use.
How could this work? I'd tell them they need to choose one of the articles to read, and that they will be asked to write a paragraph about what they've read, in response to an article-specific question I'll post. They'll be encouraged to discuss their chosen article with other students, face to face or on the WebCT discussion board, but will need to compose their own paragraph answers. To discourage copying I can have them submit their paragraphs to Turnitin as well as in answer to a WebCT quiz question. I don't know yet what kind of questions I'd ask them.
Marking this would require some extra grader hours - I'd give them a strict word limit for their answers but even marking 400+ 50-word paragraphs will be a big chore. More generally, I'd like to shift at least 5% and maybe 10% of the course mark from the midterm and final to in-class and homework activities. I guess it's time I read up on ways to incorporate peer evaluation into such activities and assignments. I'm getting hold of a book by Eric Mazur called "Peer Evaluation"; I hope this will help me shift much of the marking burden onto the students (who will learn an enormous amount by doing it).
I think peer-marking is one of the things that our new WebCT-Vista system is supposed to facilitate. I hope it's not too hard to use.
The first day of class
I've been thinking about changing what I do on the first day of classes. In past years I've basically done a fast information-dump about the course and then dived right into content (shaking them up with the role of natural selection in the origin of life).
But this year I'm hoping to shift all of the classes in this course to less information-delivery by me and more thinking and doing by them. And it's important do actually do this on the first day. So I'm going to be asking them for input on what they hope to get from the course.
I also think that my default expectations have been shifted by spending the past 6 months developing learning objectives for the first-year biology courses. Learning objectives need to be stated as actions the students should demonstrate ("can do X, can explain Y, can interpret Z", not just states we want them to achieve ("understands X, knows Y"). I'm going to tell the students this, in the context of introducing the existence of learning objectives, and then I'm going to ask them to write down for me, not what they want to learn or understand or know by the end of the class, but what they want to become able to do.
I expect this will take some prompting, so I'll give them some examples: "I want to be able to explain to my parents why my sister has Down syndrome"; "I want to breed healthier Siamese cats"; "I want to help save polar bears from global warming"; "I want to help develop an AIDS vaccine". These goals are rather lame and/or unreasonable, but their only purpose is to stimulate the students to think of other ones.
I'm hoping this activity will accomplish several things. It will give me feedback that I can use in later classes. It will give them a chance to influence the course. It will require them to write. They will be encouraged to discuss their responses with other students (I'm not sure yet how best to do this). Most importantly, they'll experience (not just be told) that they are expected to do things in class, not just sit passively and watch me.
But this year I'm hoping to shift all of the classes in this course to less information-delivery by me and more thinking and doing by them. And it's important do actually do this on the first day. So I'm going to be asking them for input on what they hope to get from the course.
I also think that my default expectations have been shifted by spending the past 6 months developing learning objectives for the first-year biology courses. Learning objectives need to be stated as actions the students should demonstrate ("can do X, can explain Y, can interpret Z", not just states we want them to achieve ("understands X, knows Y"). I'm going to tell the students this, in the context of introducing the existence of learning objectives, and then I'm going to ask them to write down for me, not what they want to learn or understand or know by the end of the class, but what they want to become able to do.
I expect this will take some prompting, so I'll give them some examples: "I want to be able to explain to my parents why my sister has Down syndrome"; "I want to breed healthier Siamese cats"; "I want to help save polar bears from global warming"; "I want to help develop an AIDS vaccine". These goals are rather lame and/or unreasonable, but their only purpose is to stimulate the students to think of other ones.
I'm hoping this activity will accomplish several things. It will give me feedback that I can use in later classes. It will give them a chance to influence the course. It will require them to write. They will be encouraged to discuss their responses with other students (I'm not sure yet how best to do this). Most importantly, they'll experience (not just be told) that they are expected to do things in class, not just sit passively and watch me.
Tuesday, November 06, 2007
How to teach about dominance
Yesterday the team of people teaching BIOL 121 had our second meeting to discuss our new learning objectives. One issue that hadn't been included in the list of objectives is dominance. I added it to the list on our Instructors' Blog, stated as follows:
Here are the figures I would use. The first three figures would be introduced at the end of the first class about how genotypes determine phenotypes (yes, I know that's an oversimplification that ignores the massive effect of environment in real organisms...).
Figure 1: Introduce lactase and lactose intolerance:
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Figure 2: Show a graph of how lactose digestion depends on the amount of lactase:
Students may need to be told that each tube contains the same amount of lactose.
(I don't know if students should be told that this is fake data.)
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Figure 3: Show the questions I'll ask about this information at the start of the next class.
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Here are the figures I would show at the start of the next class:
Figure 4: Show the first question again.
Students could be asked this question first, before being given the guidance suggested on the next figures.
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Figure 5: Remind them of the graphed data.
I've made the original graph pale, and superimposed on it the labels and numbers appropriate to thinking about the amounts of lactase in adults.
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Figure 6: Add bars showing how much lactose would be digested by each amount of lactase.
Students could be guided by asking them how high these bars should be.
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Figure 7:
Now we're back to the original question. After the guidance all students should be able to see that adults with 5µg/ml lactase digest lactose almost as well as adults with 10µg/ml lactase.
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Figure 8:
This question is intended to connect their understanding of genotypes to phenotypes. The answers should be: 0 = -/-, 5 = +/-, 10 = +/+.
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Figure 9:
The +/- heterozygotes have almost as much ability to digest lactose as the +/+ homozygotes. So they will be lactose-tolerant, and we will describe the + allele as being dominant to the - allele.
This is a lot of figures. Ideally the students would have the time to try to figure most of the steps out themselves; the figures are my ideas of the steps their thinking should take.
This lesson should also build the idea that dominance and recessiveness are not properties of alleles in isolation, but properties of relationships between pairs of alleles.
I usually tell students to ignore confusing terms like 'partial dominance' and 'incomplete dominance' and 'co-dominance', and to instead just describe any other interactions between alleles and phenotypes using more informative descriptions such as 'blending' (e.g. many pigments) or 'both phenotypes are present' (e.g. blood types A and B).
The numbers on the graphs are made-up data. Real human lactase assays are usually normalized to the ratio of sucrase to lactase, which is too confusing to present here. But here's a nice graph showing how lactase levels decline and sucrase levels rise in rats (from a page by R. Bowen at Colorado State).
Students should be able to define dominance as a particular relationship between the effects of two alleles; dominance is said to exist when the phenotype of the heterozygote is the same as that of a homozygote for one of the alleles (the 'dominant' one). They should also be able to explain that dominance usually results when a single copy of the normal allele is sufficient to give the normal phenotype when combined with a defective allele, and to predict phenotypes when given such information.Students find this very difficult, I think mainly because they are encouraged in high school to blindly accept "Mendel's Rules", and think of dominance as resulting from some mysterious gene inactivation process. At the meeting I put forward the way I have been trying to teach this concept. I was (slightly) mortified to discover how many assumptions my explanation relied on (assumptions fortunately not shared by my colleagues), so I've been trying to build a better explanatory framework, using ideas they raised.
Here are the figures I would use. The first three figures would be introduced at the end of the first class about how genotypes determine phenotypes (yes, I know that's an oversimplification that ignores the massive effect of environment in real organisms...).
Figure 1: Introduce lactase and lactose intolerance:.
.
.
.
.
.
.
.
.
Figure 2: Show a graph of how lactose digestion depends on the amount of lactase:Students may need to be told that each tube contains the same amount of lactose.
(I don't know if students should be told that this is fake data.)
.
.
.
.
Figure 3: Show the questions I'll ask about this information at the start of the next class..
.
.
.
.
.
.
.
.
Here are the figures I would show at the start of the next class:
Figure 4: Show the first question again.
Students could be asked this question first, before being given the guidance suggested on the next figures.
.
.
.
.
.
.
.
Figure 5: Remind them of the graphed data.I've made the original graph pale, and superimposed on it the labels and numbers appropriate to thinking about the amounts of lactase in adults.
.
.
.
.
.
.
Figure 6: Add bars showing how much lactose would be digested by each amount of lactase.Students could be guided by asking them how high these bars should be.
.
.
.
.
.
.
.
Figure 7:
Now we're back to the original question. After the guidance all students should be able to see that adults with 5µg/ml lactase digest lactose almost as well as adults with 10µg/ml lactase.
.
.
.
.
.
Figure 8:This question is intended to connect their understanding of genotypes to phenotypes. The answers should be: 0 = -/-, 5 = +/-, 10 = +/+.
.
.
.
.
.
.
.
Figure 9:The +/- heterozygotes have almost as much ability to digest lactose as the +/+ homozygotes. So they will be lactose-tolerant, and we will describe the + allele as being dominant to the - allele.
This is a lot of figures. Ideally the students would have the time to try to figure most of the steps out themselves; the figures are my ideas of the steps their thinking should take.
This lesson should also build the idea that dominance and recessiveness are not properties of alleles in isolation, but properties of relationships between pairs of alleles.
I usually tell students to ignore confusing terms like 'partial dominance' and 'incomplete dominance' and 'co-dominance', and to instead just describe any other interactions between alleles and phenotypes using more informative descriptions such as 'blending' (e.g. many pigments) or 'both phenotypes are present' (e.g. blood types A and B).
The numbers on the graphs are made-up data. Real human lactase assays are usually normalized to the ratio of sucrase to lactase, which is too confusing to present here. But here's a nice graph showing how lactase levels decline and sucrase levels rise in rats (from a page by R. Bowen at Colorado State).
Saturday, October 20, 2007
What does 'memorize' mean?
Last night I had a conversation with some faculty friends about teaching. We reached the common point where some of us were saying that students shouldn't have to memorize lists of facts, and others were saying that students need to know the facts before they can begin to think about what they mean. One of us made the important point that the word 'memorize' may mean different things to different people, and different things in different contexts, which (slowly) got me thinking about how we can be more clear.
We all want our students to remember the facts we think important. When we complain that students are memorizing rather than learning (student readers of this blog should note that we are just as likely to be blaming the teachers as the students for this), we mean to distinguish 'rote memorization' from our more-or-less vague concept of 'real learning'. Maybe we could speak of 'remembering without understanding' and remembering with understanding'.
I'll use the cell-division process of meiosis as an example. Students are often expected to be able to define meiosis, name the stages of meiosis and reproduce the textbook illustrations of these stages. But students can accomplish this by rote memorization or as part of a richer remembering. A student who 'really understood' meiosis might be able to explain how the consequences of meiosis differ from those of mitosis and what role this difference plays in reproduction. They might be able to draw steps intermediate between the defined stages, or move paper chromosomes to simulate the entire process. They might be able to explain the physical forces and interactions that bring about the different stages, and how the genetics principles called 'Mendel's rules' are a consequence of what happens to chromosomes in meiosis.
I'll try another example, brought up by a botanist who teaches students about how the different parts of plants transport water and nutrients. Students could simply rote-memorize the names of the structures (phloem, xylem, cambium, stomata, root hairs...) and be able to reproduce textbook definitions and drawings of them, complete with labels of the substances transported and the directions of flow. Or they could also be able to explain why plants need root hairs, why some substances move up the phloem and others down the xylem (or vice versa?), which parts of this transport consume energy and why other parts don't.
Of course a student could have used rote memorization to remember all this information. And we often test students' learning in ways that can be satisfied by rote memorization, probably because this is much easier for us to assess than is deeper understanding. Our Physics colleagues have been discovering that tests that they thought were assessing understanding were in fact being passed by rote memorization. Students could 'plug and chug' - getting the answer to a question of a recognized type by inserting numbers into a memorized formula. When physicists began to assess students' understanding by putting the phenomena into new (simpler and more familiar) contexts where formulas weren't useful, they discovered that the students could no longer answer the questions. So now Physics faculty are leading the way in devising ways to measure genuine understanding, and using these measures to identify and change weaknesses in their teaching.
In Biology we of course do try to test understanding, not just memorization. We do this by asking such questions as "Would anything go wrong if a cell started meiosis with three copies of one of its chromosomes?" or "Would a plant growing in a greenhouse on Mars need the same number of root hairs as one growing under identical conditions (light, water, nutrients, atmosphere) on Earth?" One reason that I give only open-book exams is to discourage myself from asking questions whose answers can simply be looked up in the book.
One big question for Biology faculty is whether our students should be asked to rote-memorize some information before they develop their understanding of its importance, or whether the remembering should only be built up (and assessed) as part of the understanding. I favour the latter. I have been thinking that some of my colleagues disagree, but this may be only because we've meant different things by the word 'memorize'.
We all want our students to remember the facts we think important. When we complain that students are memorizing rather than learning (student readers of this blog should note that we are just as likely to be blaming the teachers as the students for this), we mean to distinguish 'rote memorization' from our more-or-less vague concept of 'real learning'. Maybe we could speak of 'remembering without understanding' and remembering with understanding'.
I'll use the cell-division process of meiosis as an example. Students are often expected to be able to define meiosis, name the stages of meiosis and reproduce the textbook illustrations of these stages. But students can accomplish this by rote memorization or as part of a richer remembering. A student who 'really understood' meiosis might be able to explain how the consequences of meiosis differ from those of mitosis and what role this difference plays in reproduction. They might be able to draw steps intermediate between the defined stages, or move paper chromosomes to simulate the entire process. They might be able to explain the physical forces and interactions that bring about the different stages, and how the genetics principles called 'Mendel's rules' are a consequence of what happens to chromosomes in meiosis.
I'll try another example, brought up by a botanist who teaches students about how the different parts of plants transport water and nutrients. Students could simply rote-memorize the names of the structures (phloem, xylem, cambium, stomata, root hairs...) and be able to reproduce textbook definitions and drawings of them, complete with labels of the substances transported and the directions of flow. Or they could also be able to explain why plants need root hairs, why some substances move up the phloem and others down the xylem (or vice versa?), which parts of this transport consume energy and why other parts don't.
Of course a student could have used rote memorization to remember all this information. And we often test students' learning in ways that can be satisfied by rote memorization, probably because this is much easier for us to assess than is deeper understanding. Our Physics colleagues have been discovering that tests that they thought were assessing understanding were in fact being passed by rote memorization. Students could 'plug and chug' - getting the answer to a question of a recognized type by inserting numbers into a memorized formula. When physicists began to assess students' understanding by putting the phenomena into new (simpler and more familiar) contexts where formulas weren't useful, they discovered that the students could no longer answer the questions. So now Physics faculty are leading the way in devising ways to measure genuine understanding, and using these measures to identify and change weaknesses in their teaching.
In Biology we of course do try to test understanding, not just memorization. We do this by asking such questions as "Would anything go wrong if a cell started meiosis with three copies of one of its chromosomes?" or "Would a plant growing in a greenhouse on Mars need the same number of root hairs as one growing under identical conditions (light, water, nutrients, atmosphere) on Earth?" One reason that I give only open-book exams is to discourage myself from asking questions whose answers can simply be looked up in the book.
One big question for Biology faculty is whether our students should be asked to rote-memorize some information before they develop their understanding of its importance, or whether the remembering should only be built up (and assessed) as part of the understanding. I favour the latter. I have been thinking that some of my colleagues disagree, but this may be only because we've meant different things by the word 'memorize'.
Thursday, October 04, 2007
Skill-Development Objectives for First-year Biology Courses
These objectives were developed by the sub-committee we put together at the end of August. We did it in only 2 meetings!
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Understanding of the scientific process:
Given a suitable description of an experiment, students should be able to identify the hypothesis or question being addressed, the experiment’s design, the possible outcomes of the experiment, the observed results, and the conclusion.
Students should be able to construct a logical and clearly expressed argument supporting a statement.
Students should be able to make effective use of textbooks, including the table of contents, glossary, end-of-chapter summaries, figures and diagrams, and study questions.
Students should be able to identify scientific issues relevant to societal problems, and societal issues arising out of scientific advances.
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Understanding of the scientific process:
Given a suitable description of an experiment, students should be able to identify the hypothesis or question being addressed, the experiment’s design, the possible outcomes of the experiment, the observed results, and the conclusion.
- For first-year students, examples from the textbook or from everyday life are likely to be most appropriate.
- Students should also be able to identify situations where the experimental design and/or results mean that no conclusion can be made.
Students should be able to construct a logical and clearly expressed argument supporting a statement.
Study skills
- A Short Guide to Writing about Biology (Jan. A. Pechenik) is an excellent resource for writing assignments. Instructors may choose to require their students to obtain it and use it as a framework for one or more assignments.
- Some instruction should be provided in class, possibly with examples of better and worse writing, but the actual writing can be done outside of class and assessed with WebCT, through the Help Centre or by peer review.
- Students should also be given experience in verbal communication and group work by having opportunities to explain a concept to another student or small group of students.
Students should be able to make effective use of textbooks, including the table of contents, glossary, end-of-chapter summaries, figures and diagrams, and study questions.
- Students benefit from practice in constructing hierarchical summaries of information provided in textbooks and in lectures.
- Interpreting an unlabelled diagram is a good exercise.
- A textbook-based scavenger hunt for information is a good in-class exercise that could be done multiple times on different topics.
Students should be able to identify scientific issues relevant to societal problems, and societal issues arising out of scientific advances.
- Instructors may wish to choose one issue relevant to course material for in-depth consideration by the class, or have students consider a number of issues throughout the course.
- It is important that students gain experience in discovering the issues themselves, rather than simply learning about issues presented by the instructor.
Thursday, September 27, 2007
Should undergraduates learn to read scientific papers?
Over at the biology blog Sandwalk, Larry Moran triggered a discussion of whether or not undergraduates should be encouraged to read and evaluate scientific papers. He thinks they're not ready for this challenge, but a number of the people commenting think differently. Here's my contribution:
Students in my first-year biology classes have an option of reading a scientific paper and writing a report on it; this replaces 15% of midterm+final exam marks. I provide a list of papers by local authors that aren't likely to be too technical, but they can select a different paper if they like. I don't vet their paper choices, and give them only a small amount of guidance.
Those who choose to do this find it very challenging, often telling me that "I had to read the paper six times before it started to make sense!". But they also find it very rewarding; they're proud to have accomplished this difficult task, and feel that the experience will give them an advantage over other students in future courses.
Wednesday, August 29, 2007
Our courses need 'process' objectives
Last spring a group of faculty (including me) put a lot of effort into developing detailed descriptions of the curricula of our first-year biology courses. Along with this we developed a list of about 30 learning objectives - abilities we wanted our students to acquire by taking these courses.
Recently we realized that, although we had done an excellent job on the scientific content of the courses, we had overlooked the need to explicitly describe the more general abilities we want our students to acquire. This category would include advanced reading and writing skills, the ability to interpret and design tests and experiments, and such learning skills as the ability to identify the gaps and confusions in their understanding (I think Dick Cheney called these "unknown unknowns").
So on Friday a sub-group of us are sitting down to begin developing these objectives for our first-year classes.
Recently we realized that, although we had done an excellent job on the scientific content of the courses, we had overlooked the need to explicitly describe the more general abilities we want our students to acquire. This category would include advanced reading and writing skills, the ability to interpret and design tests and experiments, and such learning skills as the ability to identify the gaps and confusions in their understanding (I think Dick Cheney called these "unknown unknowns").
So on Friday a sub-group of us are sitting down to begin developing these objectives for our first-year classes.
Wednesday, August 08, 2007
Preparing for Reading Week projects
I just had a meeting with the people looking after UBC's Learning Exchange, to discuss the arrangements that will let students in my classes participate in Reading Week projects. In these projects the students will spend their week off working as part of groups enhancing the experience of children in schools located in Vancouver's poorest communities (mainly the "downtown east side").
The biggest issue for me is to be sure the projects my students do include some biology, because I want to give academic credit for this work. The nature of the projects is driven mainly by the teachers' knowledge of their students' needs, and by the interests of the graduate students who coordinate the projects, but it should be possible to make sure our projects have a biology component.
The biggest issue for me is to be sure the projects my students do include some biology, because I want to give academic credit for this work. The nature of the projects is driven mainly by the teachers' knowledge of their students' needs, and by the interests of the graduate students who coordinate the projects, but it should be possible to make sure our projects have a biology component.
Monday, July 23, 2007
Purple hair !?!
Lately I've gone back to tinting my hair interesting colours. We'll see what the students think when I start teaching again in January.
Wednesday, May 23, 2007
Preparing students to teach evolution
I just sent an email off to some faculty in the Faculty of Education, asking if they'd meet with me and a colleague to discuss how we are preparing (mostly failing to prepare) our students to teach evolutionary biology. These future teachers will be in the front ranks, defending evolutionary science against the 'war on biology' being waged by the Christian and Muslim fundamentalists. We can't complain about how they do this job if we haven't done our best to prepare them for it.
Monday, April 30, 2007
Rank, reward, filter...
I'm about to submit the final grades for my freshman biology course, which prompts some thinking about why we give grades (rather than e.g. pass/no credit).
A "pass/no credit" system accomplishes one of the functions of grading. It filters out the students who are not prepared to proceed to the next stage in their education program (or their like). When students complain (beg for special consideration), I often argue that "I've given you an 'F' for your own good", and I encourage them to think about other career plans than medical school (or Pharmacy, which is big here).
But when I fail students in their first year of university I'm also motivated by the benefits to other members of the university community. That's the filtering function - part of my responsibility is to prevent unprepared students from going on to more advanced courses. Such students are a tremendous drag on teaching; both the instructor and the other students pay a heavy price if the level of instruction has to be lowered to accommodate students who should never have been allowed to enroll.
The other functions of grading won't be satisfied by a "pass/no credit" system. One of these is ranking the students who have passed. Our university uses student grades to assign priority in registering for next year's courses. So students with good grades have first choice of the often-limited places in the courses they want, and students who have just scraped through have to put up with what's still available when are finally allowed to register.
Another function of grading is giving the best students the marks that get them scholarships and other benefits. It's not enough that a student is top of the class - if the top mark is only a B this student won't make the local equivalent of the Dean's List. With a class of 400 (well, two classes of 200), I want to give the top ten or so students A+s, even though my tough final might have left them with what would otherwise be an A-.
One final issue is consistency of grading in a big course with sections taught by different instructors. The different instructors may have to compromise our individual grading philosophies a bit to ensure that students in different sections are treated comparably. So I'm waiting for the course coordinator to give me the OK to click the "submit grades" button.
A "pass/no credit" system accomplishes one of the functions of grading. It filters out the students who are not prepared to proceed to the next stage in their education program (or their like). When students complain (beg for special consideration), I often argue that "I've given you an 'F' for your own good", and I encourage them to think about other career plans than medical school (or Pharmacy, which is big here).
But when I fail students in their first year of university I'm also motivated by the benefits to other members of the university community. That's the filtering function - part of my responsibility is to prevent unprepared students from going on to more advanced courses. Such students are a tremendous drag on teaching; both the instructor and the other students pay a heavy price if the level of instruction has to be lowered to accommodate students who should never have been allowed to enroll.
The other functions of grading won't be satisfied by a "pass/no credit" system. One of these is ranking the students who have passed. Our university uses student grades to assign priority in registering for next year's courses. So students with good grades have first choice of the often-limited places in the courses they want, and students who have just scraped through have to put up with what's still available when are finally allowed to register.
Another function of grading is giving the best students the marks that get them scholarships and other benefits. It's not enough that a student is top of the class - if the top mark is only a B this student won't make the local equivalent of the Dean's List. With a class of 400 (well, two classes of 200), I want to give the top ten or so students A+s, even though my tough final might have left them with what would otherwise be an A-.
One final issue is consistency of grading in a big course with sections taught by different instructors. The different instructors may have to compromise our individual grading philosophies a bit to ensure that students in different sections are treated comparably. So I'm waiting for the course coordinator to give me the OK to click the "submit grades" button.
Thursday, April 26, 2007
Not "hot"
My sense of responsibility to my students prevents me from reading what they're saying about me on RateMyProfessors.com until AFTER I've submitted their final grades.
Tuesday, April 17, 2007
Oral exams
One of my grad students is about to defend his PhD thesis, which got me thinking about oral exams. Most undergraduate students never experience an oral exam, but they're the best and I think fairest way to assess a student's understanding.
Usually the examining committee has several members, who each ask the candidate a series of questions. The goal is to find out the limits of the student's understanding, and the strength of oral exams is the flexibility of the questions. So when the student easily answers one question, the examiner responds with a harder question on the same general topic. If this is answered well, the next question will be even harder. Any question the candidate can't answer defines one boundary of their knowledge. The examiner responds by changing topics, again starting with an easy question and moving to harder questions if the student's answers are good, until another boundary is reached.
So taking an oral exam is a scary experience. No matter how well or how badly you are doing, you'll still spend a substantial fraction of the time dealing with questions you find very challenging, and you probably will be unable to answer some questions. But knowing that this is supposed to happen to even the best students can save you from panicking when it happens to you.
Usually the examining committee has several members, who each ask the candidate a series of questions. The goal is to find out the limits of the student's understanding, and the strength of oral exams is the flexibility of the questions. So when the student easily answers one question, the examiner responds with a harder question on the same general topic. If this is answered well, the next question will be even harder. Any question the candidate can't answer defines one boundary of their knowledge. The examiner responds by changing topics, again starting with an easy question and moving to harder questions if the student's answers are good, until another boundary is reached.
So taking an oral exam is a scary experience. No matter how well or how badly you are doing, you'll still spend a substantial fraction of the time dealing with questions you find very challenging, and you probably will be unable to answer some questions. But knowing that this is supposed to happen to even the best students can save you from panicking when it happens to you.
Friday, April 06, 2007
Gender bias in students' expectations
I'm still seething over a couple of postings an anonymous student made to the discussion board for my freshman biology course. I had asked a colleague (Dr. X) to give two lectures, in exchange for three I had done for him earlier in the term.
I've already responded on the discussion board to the implication that when I'm not lecturing I'm resting (see posts below), but here I want to point out the implicit gender bias in this student's expectations.
The student views Dr. X's research work as more important than his teaching responsibilities. (I had told my students he was doing botanical research, but in fact he was accompanying his wife on a trip combining her research with a vacation for them both.) The student assumes that of course I should make sacrifices to support this work.
On the other hand, although I run a much larger research program than Dr. X, I am seen as only a teacher. And in addition to teaching, I'm judged on how deeply I appear to care about my students.
These different expectations are one of the many reasons women faculty have a hard time. Students make excuses for male faculty (who they see as having more important things to do than teach), but expect women faculty to be substitute mothers, sacrificing any other goals to take care of their students. On Wednesday the students will do their teaching evaluations, and I expect as usual to be criticized for insufficient nurturing.
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Here are the discussion board posts:
From an anonymous student:
I've already responded on the discussion board to the implication that when I'm not lecturing I'm resting (see posts below), but here I want to point out the implicit gender bias in this student's expectations.
The student views Dr. X's research work as more important than his teaching responsibilities. (I had told my students he was doing botanical research, but in fact he was accompanying his wife on a trip combining her research with a vacation for them both.) The student assumes that of course I should make sacrifices to support this work.
On the other hand, although I run a much larger research program than Dr. X, I am seen as only a teacher. And in addition to teaching, I'm judged on how deeply I appear to care about my students.
These different expectations are one of the many reasons women faculty have a hard time. Students make excuses for male faculty (who they see as having more important things to do than teach), but expect women faculty to be substitute mothers, sacrificing any other goals to take care of their students. On Wednesday the students will do their teaching evaluations, and I expect as usual to be criticized for insufficient nurturing.
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Here are the discussion board posts:
From an anonymous student:
I felt really bad for him. He was just given a package of slides and then tried to teach from there. I thought a lot of people were really disrespectful. Like if you went the monday lecture and found him insanely boring, why did you come to the one on wednesday just so you could talk the whole time and then make a huge scene by leaving early?My response:
Hi everyone,From another anonymous student:
Dr. X normally teaches another section of Biology 121. He taught
these two classes for me because I had taught three classes for him in
late February, while he was in Thailand.
He did not have any prepared material that he thought would be suitable
for my students, so I provided him with copies of the slides I used last
year, thinking that he could use them as a framework to develop two
classes on sustainability. I did not expect him to simply show my
slides, and I apologize for any problems with the classes he taught.
Dr. Redfield
Its quite rediculous that she asked Mr. X to teach for her although she helped him(I deleted this post, and last night a new one appeared - same sentiment and same spelling error so probably the same student.)
teach 3 classes. Mr. X was away for a reason, but dr. Redfield is just taking a
break and not being responsible for our class. Just so dissappointed.
I actually disagree on that. Some parts were interesting, but this teaching skill was not good. Dr. Redfield's teaching method was really better and have the skill to actually crab your attention! However, I am quite dissappointed that she wasn't able to teach our class. She taught Dr. Xs class because he was away to Thailand, but now he is taking over her class while she is resting. This really shows that she is very unresponsible for our class. She is a good, interesting and smart prof, but maybe she needs to care more.And here's my response.
!!! RESTING???
Pardon the 'shouting', but I've been working night and day, holidays and
weekends, on this course; just check the dates and times of my
Discussion Board postings. Since my last lecture to you I've taken
exactly one day off (yes, it was a weekday, but I worked on all of the
weekend days).
If my lectures are interesting it's because of the work I put into them.
For example, I've spent part of the Easter weekend working on
Wednesday's final lecture. This is a lot of work because I've decided
to replace about half of what I had prepared with material from the new
IPCC Report on climate change. I'll be spending much of today on it too.
I also spent part of the Easter weekend compiling and posting the PRS
marks. This including tracking down the errors students had made in
entering their student numbers so they would get the marks their answers
have earned.
I spent part of it analyzing and posting the Reading Quiz marks. This
included going back over the original 'opt-out' quiz to find those
students who had never realized that if they weren't going to take the
quizzes they needed to actively opt out. (About 15 students had marks
of zero; I discovered that they had not opted out but never taken a
quiz, so I opted them out retroactively.)
I spent part of it reading and responding to Discussion Board postings.
I spent part of it working on the final exam.
I spent part of it reading reports of students' projects.
And I spent part of the weekend doing an experiment in my research
laboratory. Today (Easter Monday) I may even find time to analyze the data.
At the end of February I took valuable time away from preparing my grant
proposals to teach Dr. X's classes, so that he could spend an extra
week in Thailand. We agreed in advance that he would repay this favour
by lecturing to my classes, freeing me to catch up on other
responsibilities.
I realize that students don't have many opportunities to see the work
their professors do outside of class. But 'resting' is the last thing
we have time for.
Dr. Redfield
Thursday, April 05, 2007
Last class: teaching evolution
I won't be teaching evolution in this class. Instead I want to address the problems raised by the sophisticated war being waged against evolution by Christian and Islamic fundamentalists. Nobody else I know covers this in their biology classes, but we can't just blame the high-school teachers for doing an inadequate job of teaching evolution, when we're the ones responsible for teaching the next generation of teachers.
Last year I taught this in the middle of the term, at the end of the Evolution section, but this year I've moved it to the last class. I'm also going to cut down on the mass of examples of fronts in this war, both to allow more time for introducing the resources available for biology teachers, and because we need to allow time for end-of-term teaching evaluations.
It's important to not put all the blame on the Christians. The richly funded Islamic fundamentalist group operating under the name Harun Yahya is not well known in the West, but they produce an enormous amount of very slick anti-evolution propaganda.
Last year I taught this in the middle of the term, at the end of the Evolution section, but this year I've moved it to the last class. I'm also going to cut down on the mass of examples of fronts in this war, both to allow more time for introducing the resources available for biology teachers, and because we need to allow time for end-of-term teaching evaluations.
It's important to not put all the blame on the Christians. The richly funded Islamic fundamentalist group operating under the name Harun Yahya is not well known in the West, but they produce an enormous amount of very slick anti-evolution propaganda.
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