By PETER OMMUNDSEN
Problem-based learning (PBL) is an exciting way to learn biology and is readily incorporated into large classes in a lecture hall environment. PBL engages students in solving authentic biological case problems, stimulating discussion among students and reinforcing learning. A problem-based learning environment emulates the workplace and develops self-directed learners. This is preferable to a mimetic learning environment in which students only watch, memorize, and repeat what they have been told.
The examples given here are suitable for use in a first year college biology lecture theater, but the method is applicable to any class size and educational level. [A more detailed explanation of PBL in Biology may be found in Chapter Four of INSPIRING STUDENTS, published in 1999 by Kogan Page.]
METHOD FOR INSTRUCTORS
(1) Form Small Groups
You may decide to devote all or part of a class session to PBL, but students must form small work groups during that time. Ask the students to form groups of 3-5 people, or assign the groups yourself or by lottery.
(2) Present the Problem
Present the students with a brief problem statement (preferably on a printed work sheet, an example of which is shown below), e.g., "A 28-year-old man appears to have osteoporosis." In some cases a video clip or specimen might be used as a trigger. Emphasize to the students that they are dealing with an authentic case history. Bizarre problems work best [more examples follow]. Prior to class you should review the case history and arm yourself with data that can be released incrementally (progressive disclosure) as the case proceeds. There is a comprehensive data set for the osteoporosis problem in the New England Journal of Medicine, 1994, 331:1056-61; 1088-9. Needless to say, the students should not be given the reference, as the objective is to solve a problem, not read a solution.
(3) Activate the Groups
Ask the groups to brainstorm possible causes of the osteoporosis. Each group will have to discuss, review, or investigate the biology of bone, including the role of osteoblasts, diet, vitamin D, parathyroid hormone, growth hormone, calcitonin, kidney function, etc. This is when much learning occurs, as the students help each other understand the basic biology. PBL students must reflect upon biological mechanisms rather than just memorize facts (as might occur in some traditional lecture-only courses). The instructor circulates among the groups, providing assistance but not solutions. The groups may well explore avenues unanticipated by the instructor. This is highly desirable and should not be discouraged. The instructor should avoid controlling the agenda of the groups. Each group ranks its hypotheses in order of priority and prepares requests for more data. (E.g., for calcium deficiency hypothesis -- "What did he usually eat?")
(4) Provide Feedback
Ask that a rep from each group place their top priority hypothesis or data request on the chalkboard (if already entered by another group, place their second choice, etc.). If this is not practical, ask for oral suggestions from the groups when the small group work is halted and the class is reconvened. Student suggestions may include --
- Low calcium diet
- Low density of vitamin D receptors
- Calcitonin deficiency
- Excessive PTH
- Chronic acidosis buffered by salts mobilized from bone
The small group work can be stopped and the instructor can briefly discuss the ideas with the entire class. It is important to value every contribution, to assist the students in analysis of the biology involved, and to provide further information [he was not immobile, he had a normal diet, etc.]. The students can be prompted for data requests: "If you could ask for just three test results from examination of this man, what would they be?"
It is not likely that the students will solve a problem on the first pass, and the feedback from the instructor motivates the next round of small group work. The students could now be told that the man's lumbar spine density is 3.1 standard deviations below the average age-matched healthy female (osteoporosis = 2.5+ SD), his height is 204 cm, his left middle finger is 10 cm, and knee films show open epiphyses. (The students should now be able to figure out that the man may still be growing at age 28). The cycle of small group work and instructor feedback can be continued during the current class session or on future occasions. The key to managing a PBL session is providing continual feedback to maintain student enthusiasm while simultaneously prolonging the resolution of the problem to ensure that adequate learning occurs.
(5) Ask for a Solution
At this point in our example the groups will likely focus on the hormones required for epiphyseal closure and bone mineralization. They may ask you for serum estrogen levels (high) which will suggest estrogen-resistance. Were estrogen receptors defective? (Yes.) When a reasonable number of groups have solved the problem, you might request a brief written analysis from each group describing the biology involved in the case. Students may be asked to include certain key words in their reports. If you wish to further pursue this case at a later date you could tackle the genetics of the defect. (C to T transition in the estrogen receptor gene in both alleles causing a premature stop codon; both parents heterozygous with consanguinity in the pedigree.)
METHOD FOR STUDENTS
Effective problem-solving requires an orderly approach. Problem-solving skills do not magically appear in students as a result of instructors simply throwing problems at them.
Our students use the following heuristic: "How to make a DENT in a problem: Define, Explore, Narrow, Test."
(1) Define the Problem Carefully
What exactly are you trying to determine? Does the problem have several components? If several, state them separately. Does everyone in the group agree with the way the problem has been framed? Ask group members to "think out loud," as that slows down their reasoning and enables people to check for errors of understanding.
(2) Explore Possible Solutions
Brainstorm ideas that may contribute to a solution. Justify your ideas to group members. Clarify for them the biology involved. Have them paraphrase your ideas. Listen carefully to the ideas of other group members and give positive feedback. Make a list of learning issues. What do we know? What don't we know? Is this problem analagous to any past problem? What core biological concepts may apply to this problem? Assign research tasks within the group.
(3) Narrow Your Choices
After developing a list of hypotheses, sort them, weed them, and rank them. List the type of data required to test each hypothesis. Give priority to the simplest, least costly tests. It is easier to get information on the diet of a subject than it is to do sophisticated biochemical tests.
(4) Test Your Solution
Seek from your instructor the data that you need to test your ideas. If all your possible solutions are eliminated, begin the cycle again: define, explore, narrow, test. When you encounter data that confirm one of your hypotheses you may be asked to write a biological explanation of your solution and justify it using the available evidence.
MORE CASE PROBLEMS
Following are examples of typical case problems that have been culled from biological journals and that have been successfully class-tested at the first-year college level.
A sample student work sheet may be seen by clicking here.
Case problem SOURCES for these examples are shown here for the benefit of instructors, but normally sources are NOT given to students as that would defeat the purpose of PBL.
A 58-year-old woman experienced attacks of confusion: she would repeat the same question 30 times even though it was answered for her each time. [New England Journal of Medicine 315:1209-19.]
This is a good introductory case, as the students are able to generate a wide range of ideas: Alzheimer's Disease, trauma, alcohol abuse, atherosclerosis, arrhythmia, hypotension, cancer, epilepsy, diabetes, hypocalcemia, emphysema, dehydration, hypoglcemia, stroke, etc. The students perceive that the class as a whole is a credible learning resource, and the instructor can help the class reflect upon the biological implications of each suggestion.
Eventually the students will ask the circumstances of the woman's attacks (e.g., "Following alcohol consumption?") When the students learn that the attacks occurred in the late afternoon, they will likely focus on diet and blood sugar. The instructor might at this point present a short talk on carbohydrate function and blood sugar regulation. This can be done using a transparency, with copies available to the students. It is important in a PBL environment to minimize the time required for note-taking.
The students will ask for information on the woman's blood glucose level (1.6 mmol/L) and urine glucose level (zero). The student groups can now brainstorm and investigate possible causes of the low blood glucose: glucagon deficiency, insulin poisoning, anorexia nervosa, extreme exercise, etc. They may ask for an x-ray image of her abdomen, which the instructor can display as a transparency copied from the article. The students can be assisted in identifying the anatomy, including an abnormal mass in the pancreas (an insulin-secreting tumour). Additional discussion and learning opportunities can be generated by displaying copies of the ultrasonogram, angiogram, histopathology, etc.
The students in each group may then collaborate in writing a brief report that explains the biology of the case.
(2) A Case of Falling Cats
Sabrina the cat fell 32 stories from a New York skyscraper and easily survived, as do most cats that fall from skyscrapers, especially those that fall more than several stories. Not so for humans. Why? [Natural History Magazine, August 1989: 20-26.](3) A Case of Puzzling Parenthood
This intriguing case requires students to confront (or review) fundamental concepts that have wide application in biology, including allometry, momentum, stress, compliance, friction, surface area, acceleration, equilibrium, adaptation, and natural selection.
A woman with type AB blood gave birth to a child with blood type O. A second type-O child was born six years later. [Nature 277:210-211.]
This case appears to contradict Mendelian inhertiance, which the students will be obliged to thorougly review, but it also demands that they make a rigorous examination of meiosis, gametogenesis, fertilization, and early development in order to propose some credible explanatory mechanisms.
(4) A Case of Wilting Plants
A farmer was alarmed to notice tomato plants that were stunted and withered.
This case initially requires the students to carefully reflect upon many basic concepts of plant anatomy, histology, physiology, ecology, and pathophysiology. Students might discuss and explore possible effects of soil quality, water relations, humidity, transpiration, hormones, and nutrition. Students should be encouraged to explore examples of pathogenic mechanisms, perhaps involving TMS, wilt fungi, wilt viruses, stunt viruses, and wilt bacteria.
Ultimately the cause may be attributed to ABA deficiency, and the instructor might suggest this by introducing evidence of viviparity. Students can then focus on the roles of ABA and ethylene, and further work might address the genetics of the defect. .
There is a comprehensive literature on ABA-deficient mutants, and many easily accessible web resources, e.g., Plant Biology 2000 Abs 706, XVI International Botanical Congress Abs 6158, etc.
(5) A Case of an Unusual Pregnancy
A 94-year-old woman admitted to hospital for pneumonia had a swollen abdomen. A CT scan revealed a fetus. The woman had dementia so was unable to explain what had happened. [New England Journal of Medicine 321:1613-14.]
This case prompts exhaustive brainstorming of all aspects of reproductive physiology and will produce many imaginative hypotheses.
(6) A Case of Declining Biodiversity
In a coyote-control experiment coyote population density was greatly reduced. The number of rodent species then declined from ten to only two! Rodent species richness did not change on comparison areas where coyote density remained high. [Journal of Wildlife Management 63:1066-81.]
This case opens many avenues of biology for exploration, including trophic levels, population regulation, population limitation, competitive exclusion, niche breadth, keystone species, umbrella species, predator control policy, biodiversity, and species richness.
(7) A Case of Aversion to Sugar
A 24-year-old man experienced abdominal pain, diarrhea, and distention whenever he consumed sugar. This was a life-long problem. [New England Journal of Medicine 316:438-442.]
This case ensures that students master the taxonomy of carbohydrates, and the physiology of carbohydrate digestion and absorption.
(8) A Case of a Tight Grip on the Toothpaste
A woman encountered her 30-year-old daughter squeezing the toothpaste and unable to let go. Later that day the daughter was found holding the doorjamb and unable to move forward. [New England Journal of Medicine 317:493-501.]
(9) A Case of Murder
Obtain a selection of DNA-typing profiles (RFLP autorads or STR electropherograms) from local police, and construct a brief but equivocal fictional case history. Divide the class into to groups of five – each group with one judge, two prosecutors and two defense attorneys. Each student should have a copy of the case and copies of raw DNA profiles. (The old autorads force the students to measure by hand.) Each side must argue the evidence before the judge and submit to the instructor a brief written report along with a written decision from the judge. This exercise demands that students help each other to thoroughly understand the genetics, and the proceedings result in much hilarity. It is desirable to introduce some complexity, for example we included an autorad from blood on a knife that contained specimens from several people.
Another good source of DNA typing problems is wildlife census data from hair traps (e.g., grizzly bears).
121 cases of illness were characterized by sleeplessness, headache, tachycardia, shortness of breath, sweating, tremor, heat intolerance, and weight loss. [New England Journal of Medicine 316:993-998.](11) A Case of Deadly Exertion
A fitness test of applicants to a fire department resulted in 32 hospitalizations with back pain, muscle pain, and reduced urine output. One person died. [MMWR 39:751-6.]
The students will at some point address muscle physiology. What happens when muscle cells break during exertion? What are the consequences of hyperkalemia on the heart? Where does all the potassium originate? What are the effects of myoglobin on the kidneys? What is the impact of oxygen free radicals produced by damaged muscles?
(12) A Case of the Gritty Lungs
An 80-year-old woman suffered from confusion, falls, and fractures. Her lungs were gritty like hard sponges. [New England Journal of Medicine 315:1209-19.]
(13) A Case of Many Illnesses
A one-year-old boy began to have recurrent bacterial infections including pneumonia, sinusitis, and middle ear infections. This pattern continued, and at age 9 he developed Hodgkin's disease. He is HIV-negative. [New England Journal of Medicine 320:696-702.]
(14) A Case of a Short-Lived Male
In one mite species of the genus Adactylidium the male is born, does nothing, and dies within a few hours. What evolutionary selection pressures might have shaped this life-style? [Stephen J. Gould, The Panda's Thumb (book) pp 73-75.]
(15) A Case of 25 Eggs per Day
An 88-year-old man had eaten 25 eggs per day for many years, yet his serum cholesterol was only in the range of 150-200 mg/dL. [New England Journal of Medicine 324:896-900.]
(16) A Case of Exercise Aversion
An 18-year-old man fatigued quickly during exercise. [New England Journal of Medicine 324:364-9.]
This is an excellent case for application of principles of cellular energy metabolism.
(17) A Case of Mass Fainting
Four hundred people at a rock concert collapsed or experienced faintness, with possibly as many as six different proximal causes. [New England Journal of Medicine 332:1721.]
Students must reflect on the biology of a number of organ systems: fasting hypoglycemia, fasting acidosis, orthostasis, hyperventilation-induced cerebral vasoconstriction, Valsalva pressure from screaming and crowding, etc.
(18) A Case of Dead Trees
A forest patch was logged, then replanted, but within seven years the newly planted trees began to die. [Local example -- acid precipitation, leaching of soil nutrients, inadequate woody debris left on ground as a soil nutrient bank after logging.]
(19) A Case of a Rattlesnake Warning
A rattlesnake can flick its tail 90 times per second. (Compare that to the speed at which you can flick a finger and address the possible differences in muscle biology.) [Science News 150:53 July 27 1996.]
(20) A Case of Lassitude
A 26-year-old woman complained of weakness and lassitude. Her blood pH was 7.56 and her arterial pCO2 was 45.2 mMol. Blood pressure was 90/60.
This is a terrific case, well presented, with a wealth of data on blood gas and electrolyte values. The case requires students to consider the functional interaction of several organ systems. [Nephrology Dialysis Transplantation 16:1066-1068.] A printable pdf copy is available at Teaching Point.
Copyright 1996, 1997, 1998, 1999, 2000, 2001 Peter Ommundsen
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Case-based learning in biology