Overview and Rationale
Teach evolution in three days, bacteria and viruses in one day, and human body systems—if you have time to get to them—in four days. What are students supposed to learn about these major topics in biology on such a tight time schedule? And yet, that's exactly what biology teachers are asked to do with the pacing guide we are given to follow in teaching high school Biology I classes in my school district. The only way to accomplish this is to integrate these topics into one cohesive unit rather than teaching each one separately. In addition, the integration of the topics should help students understand how these sometimes seemingly disparate topics are connected. It has been said that nothing makes sense in biology except in relation to evolution. With this unit, I will be using evolution to help students understand how their bodies work and why they sometimes don't seem to work so well. By bringing in some of the ideas about evolutionary medicine, I hope to help my students see that evolution is not just about the past, but that it is happening all around us, and in us, and affects our everyday lives.
This two week unit will begin with an introduction to the theory of natural selection and how natural selection causes changes in populations. Since the previous unit will be on genetics, I will pose the question, "If individuals with unfavorable characteristics, like genetic disorders, would have been unlikely to survive in an environment with no doctors or medicines, then why are people still being born with these disorders today?" The class will then participate in an activity that simulates how the sickle cell allele might increase or decrease in frequency, depending on the type of environment. At the end of the activity, students will learn about the disease's connection to malaria, and the life cycle of the Plasmodium parasite and the Anopheles mosquito vector. They will observe normal and sickle-shaped red blood cells on prepared slides and investigate the effect of blood cell shape on the function of the circulatory system using models of sickle and normal red blood cells to help them visualize how the shape of the cells leads to the symptoms of sickle cell anemia.
Other systems—digestive, respiratory and nervous systems—will be described in terms of their evolutionary adaptations and examples of genetic disorders of those systems which have persisted in populations in spite of their costs to the individual. Students will study the effects of obesity and diabetes on the digestive system, and their link to our ancestors' diets and climate change. I will have students look at their own diets and analyze how they might be setting themselves up for problems with obesity and diabetes and what they could do to eat a diet that takes into account their evolutionary history. They will study the nervous system and the effects of phenylketonuria (PKU) and Huntington's chorea and why these conditions remain at such relatively high frequencies in certain populations. Finally they will look at the effects of cystic fibrosis on the respiratory and digestive systems and how heterozygote advantage or genetic drift can affect the frequency of diseases.
The final system we will cover is the immune system. We will begin with a lab on antimicrobial product resistance. Students will expose E. coli bacteria to various types of antimicrobial products and look for colonies of resistant strains. This will be followed by a discussion of the arms race we are in with infectious microbes through the use of antibiotics, vaccines, and our own immune systems, and how we might avoid an arms proliferation, whereby microbes become even more virulent. Students will learn about how our immune system works and how it develops as we grow, in response to our environment. They will look at a variety of infectious diseases and their agents—HIV, Influenza, Smallpox, and Streptococcus—and how the viruses and bacteria that cause these diseases have adapted to survive and reproduce so successfully.
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