Lesson Plan: VIRUSES



Lesson Plan: VIRUSES

Lesson Overview

The students will be presented with the viruses as separate entities of a living world, their structure and function, and how viruses interact in the environment, causing an infection and a disease. The activities comprise gathering student’s ideas about what is a virus, building a compare/contrast diagram bacteria vs. viruses in class, and using them to build a class naïve model of a virus. With data provided in handouts as authentic data for HIV virus, and with using Net Logo model of virus biology as related to the spread and epidemic, students will build two models: “What is a virus’, and ‘How does the virus cause a disease and spreads amongst human population’ . Students will work in pairs and in groups of 4-5. In the end, students will present models in class and discuss each other’s models. They will agree on the class consensus model about ‘How does the virus cause a disease and spreads amongst human population’. Throughout the lesson the teacher will point out the scientific practices and nature of science, discuss them with students, explain how they are used and encourage the students to use them as scientists do.

This lesson is linked to the previous lesson on bacteria, how they cause diseases, and the phenomenon of parasitism, and to the next lesson about Protists, thus proceeding to the organisms with more complexity in taxonomic grouping.

Learning objectives

Content

o A typical virus is composed of a core of either DNA or RNA, surrounded by a protein coat, or capsid.

o Viruses can only live and reproduce inside the host cells, using the host cell reproductive system.

o Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium.

o Viruses spread amongst populations of their hosts. Depending on the biology of the virus-host interaction, viruses are more or less likely to cause an epidemic.

Scientific practices

o Modeling – making predictions, generating hypotheses, test hypotheses, using scientific data, generating evidence, revising models.

o Public discussion, argumentation

Nature of science

o Scientists build models and theories to explain natural phenomena

o Models and theories change in face of new evidence

Standards

New Jersey Core Curriculum Content Standards for Science

o A. 4. Relate disease in humans and other organisms to infections or intrinsic failures of system.

o A. 1. When making decisions, evaluate conclusions, weigh evidence, and recognize that arguments may not have equal merit.

o 5.1 A. 3. Engage in collaboration, peer review, and accurate reporting of findings.

Student’s conceptions

Without much experience in modeling, students will tend to think of models as concrete, fixed replicas, a “copy” of reality. Students will tend to think to think that the purpose of models is to show or describe scientific phenomena. They believe the value of models to be simply the fact that they exist. In this case, the student has a passive role in relation to models: “models are created for me to see what is going on.” (Summarized after M. Windschitl and J. Thompson, Teaching About Science Ideas – As Models)

It is hard for students to grasp how viruses are different from bacteria. They both can make us sick. They struggle with the notion of where do viruses come from, how do they make us sick, where can they be found, and are they alive or not. Students especially struggle with more complex concepts, like virus-host interaction and epidemiology of the viruses (summarized after talking to the high school biology teacher).

Students are familiar with the concepts of DNA, RNA, enzymes/proteins, and have been already shown the tests for DNA and proteins (DNA extraction, DNA analysis and protein analysis). They are familiar with what a cell is and the function of organelles (e.g. DNA synthesis and DNA transcription into RNA in nucleus, protein synthesis/translation of mRNA in ribosomes, and the enzyme function in these processes). They are familiar with the concepts of infection, parasitism, and pathogenicity, from their previous lesson on bacteria.

Assessment

Assessed will be artifacts that students produce (embedded formative assessment) during the model-based inquiry lesson in a form of:

o their models (activity 3: individual worksheet Model of What is a virus - understanding of content, scientific practice: modeling; Activity 6: );

o Arrow diagram (activity 6: individual worksheet Strength of evidence – comparing evidence from two models, scientific practice: argumentation, NOS: evidence changes models and theories).

Material and preparation

o Handouts: 1) EM micrographs of HIV in a T cell and EM micrograph of HIV purified from AIDS patient’s blood. 2) RNA analysis of HIV RNA – hybridization, PCR, sequencing. 3) Analysis of viral proteins, ELISA, Western blot. 4) quantitative and qualitative PCR and ELISA test results from a healthy and sick patient’s blood, 5) blood cell counts in AIDS patients. 6) Bacterial analysis of AIDS patients blood results. 7) Results which show that HIV infected T cells get destroyed by healthy macrophages. All data in handouts are prepared from scientific papers. One copy of each handout per student.

o Videos: What is a virus? How does HIV cause disease? The action of antiviral drugs on viral entry and replication:

o Wilensky, U. (1998). NetLogo Virus model. . Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

o Worksheet for a model ‘What is a virus’, one per student

o Worksheet (Arrow diagram) for comparing evidence between class and a group model, one per student.

o 4 markers of different color per group (3-4 groups), 1 poster paper per group

The lesson takes time of two normal school periods (2 times 42 minutes).

Activities

1) What is a virus (10 min)

Tell the students that he/she will show them a short one minute video animation that they should observe closely. The video is an animation of a HIV virus which looks like an alien spaceship or a strange planet rolling trough the space, landing on some kind of a surface, sinking in and coming in a different shape. The teacher will ask students what they think this animation represents. Students may or may not guess that it is a virus. The teacher may help them by asking if they think that it is a form of life. By asking more questions of what makes things alive and what kind of a life form this may have represent, the teacher leads the student discussion toward the question ‘What is a virus?’, ‘What makes it a virus?’, and ‘How are viruses different from bacteria’ (that they have learned about in a previous lesson). The teacher makes a compare/contrast diagram on the whiteboard – a table with two columns, one for bacteria and one for viruses, with collected ideas of how they are similar and how they are different. The teacher encourages the class discussion by asking students to explain and express what they think.

2) Modeling What is a virus – naïve model (15 min)

Announce that they are together going to find out what is a virus by building a model of a virus. The teacher explains that this is what scientists do when they explain phenomena in nature. They start with asking themselves a question, and than they put down everything that they already know about it or know about similar phenomena and try to construct an explanation of ‘What is it’ or ‘How does it work’. They think a lot about it and what evidence would help them to find a better and finally the best possible answer. They form hypotheses (predictions), test them by designing proper experiments, and continue searching and thinking with the help of the model that they make better and more complete with every new evidence that supports it or refutes it. They keep changing their model until they all agree that it best explains the phenomenon And…this is how we are going to find out what a virus is. The teacher starts gathering student’s ideas and puts them on the whiteboard.

The students will draw on the knowledge that they have from previous lessons, of what they know about viruses from newspapers, TV, family talks, and the earlier class discussion – comparison with bacteria. They will probably come up with ‘small’, ‘cause disease’, ‘infectious’, ‘epidemics’, ‘AIDS’, ‘HIV’, other diseases caused by viruses, virus testing (from blood?)….The teacher will encourage their thinking and elicit their ideas by asking questions: ‘Are they a life form?’, ‘What defines life?’; ‘Do they have cells?’…in order to lead them into thinking about growth (do they metabolize, do they contain proteins), reproduction (do they carry genetic information), do they have membrane (like cells), how do they obtain energy, do they ingest, excrete…? The teacher will put their ideas on the whiteboard and encourage thinking, discussion, until the model(s) start shaping. Than the teacher will ask the students if they think if we have a model or several models of viruses in correspondence with all our ideas about what we think it could be and with what we know there is. The teacher will be very pleased with all the good explanations and ideas that everybody contributed to shape up our very first model of what the viruses are. The teacher will also ask the students how we know about all this. After a short discussion and letting the students come up with how do we know, the teacher will point out that scientists get their evidence from scientific data. Every idea needs to be supported by good reliable data, which could be confirmed by other scientists, before they claim anything, like: what we see here, or what caused this and this disease, is a virus. The teacher will ask the students if they could come up with the ideas how would we make our model more scientific, what information – data do we need to make it more complete? How do we test our ideas? The students may come up with the ideas like laboratory testing, looking under microscope, transmitting it from one to next organism…..

3) Modeling What is a virus – revised (scientific) model (15 min)

The teacher will ask students to pair, and will distribute worksheets and handouts with data about HIV virus – where it’s found and its components (electron micrograph of a host lymphocyte cell harboring viruses with clearly indicated size, EM of isolated HIV particles from blood, RNA and protein analysis, action sites of antiviral drugs). The students will be asked to make their model of a virus and explain it. Modeling How does HIV cause a disease and epidemic (20 min)

The teacher will tell the students that they are going to watch another short video about HIV and AIDS. There are myths about the two which cause a lot of confusion with tragic consequences, although there are scientific facts and theories available which could clarify confusion and prevent a lot of tragic outcomes – and this is one of the things science exists in society. The teacher will show only a part of a longer video about Top ten myths about HIV/AIDS. Only the part where a physician/scientist is presenting the evidence for a clear connection between HIV and AIDS will be shown. The teacher will ask the class ‘How does the HIV cause the disease’. After gathering the ideas from the class by asking questions to elicit more ideas (what does the HIV do? How does it enter the cells? What does it do to the cells that make a person sick? How come we cannot get rid of HIV like with other viruses? Are all people susceptible – getting infected? Is there immunity? Does the virus get passed (transmitted) every time two people are in contact? Does the virus spread easily? Does everybody infected die? Will it ever stop spreading? Under which conditions? What can we do to stop it? How do we do that?) and directing them in the way of the possible mechanism behind it. The teacher writes all ideas on the whiteboard and points out that we are together going to build a model of ‘How does the HIV cause a disease and spreads’. The teacher starts questioning the ideas on the board by asking ‘how do we know’, ‘How can we find out’. The students may have ideas like we look into the sick cells, or we do experiments . What does the virus do there that could make a person sick? How can we test that? What experiments could we do to test that?

After the class discussion and all ideas on the whiteboard, the teacher will ask the students to form groups of 4-5, and make their group model of ‘How does the HIV cause a disease and spreads among human population’ and discuss how could they find out if the predictions in their models are correct. The teacher than introduces them to the Net Logo model of the virus spread. Together with students, the teacher will make sure that all the parameters are understood and connected with what has been learned trough the discussion in class and building of their naïve group model. The teacher will ask the students to predict what will happen before manipulating parameters, and than run the experiment to test their ideas. The teacher will encourage them to test several ideas of what will happen, test them using Net Logo, and record data, analyze and discuss data and generate evidence or counterevidence for their claims. The students are asked to keep revising their group model of ‘How does the HIV cause a disease and spreads among human population’. The teacher will tell the students to make their best guesses, think thoroughly, discuss with each other, and respect everybody’s ideas, but most important – think of how to test them. In addition to that, they can ask for more data, and the teacher will help to find them. The teacher distributes handouts with data about the qualitative and quantitative testing of HIV, blood cell counts, parallel tests for bacteria, and evidence that the infected lymphocytes get destroyed by healthy lymphocytes and macrophages in patient’s blood).

The students get the markers and a poster paper to compose their group model on. The teacher walks around and asks questions like ‘How do you know’, ‘what data would support that’, ‘How could you find out’, ‘Please explain more”….to encourage student’s thinking, and to make sure that they stay on task, and that everybody is participating.

4) Class presentation and discussion (20 min)

Students will present their group models in class. The teacher will remind them that this is how scientists make their thinking and their work public (conference or scientific paper), for everybody and especially for other scientists to see, think about, and judge how close it comes to best explaining what some phenomenon is or how does it work. Scientists than gather all good work and ideas and make new theories or change old theories into better ones, because the new ones explain phenomena better, they are supported by new, more complete and more reliable evidence. This is how the scientific knowledge grows. Here, they are a small scientific community, building their own scientific knowledge about how does the HIV cause a disease, and they are going to try their best to present their ideas in models that they have made to each other. The students are asked to be concise, and provide support for every claim that they make (how did they find out, how do they know). They will present the Net Logo data that they used to generate the evidence for their conclusions/claims. They will use Net Logo projected on the screen to show their experiment. Other groups/students will be asked to listen carefully and pay attention to how do their fellow students construct their ideas, how did they support them, do they agree or disagree and why so, ask questions for more clarification, and provide constructive critiques/suggestions for each other. The students will be all the time encouraged/reminded to explain, reason, argue respectfully. They will decide which ideas are the best and why, and they will make a class consensus model that they will all agree. They will identify what could be done better to understand how HIV causes a disease, are all viruses parasites, do they infect only human, and what virology as a science is. The teacher will point out the issue about the evidence, what is a good and what is a week evidence, how do we use it to support our claims. The students will draw and explain their class consensus model.

5) Homework – or completed in class if time permits

The students will get a worksheet with two columns, one for the evidence supporting the class consensus model, and the other for evidence supporting their group model. They will indicate using arrows (arrow diagram) which evidence is strong, medium, and weak. Below the diagram they will explain what made them decide about the strength of each evidence. They will be advised to use Net Logo in order to repeat experiments if they would like to check the evidence.

About Net Logo VIRUS model

This model simulates the transmission and perpetuation of a virus in a human population. Ecological biologists have suggested a number of factors which may influence the survival of a directly transmitted virus within a population. (Yorke, et al. “Seasonality and the requirements for perpetuation and eradication of viruses in populations.” Journal of Epidemiology, volume 109, pages 103-123)

The model is initialized with 150 people, of which 10 are infected. People move randomly about the world in one of three states: healthy but susceptible to infection (green), sick and infectious (red), and healthy and immune (gray). People may die of infection or old age. When the population dips below the environment’s “carrying capacity” to support the virus (set at 700 in this model) healthy people may reproduce healthy and susceptible offspring.

The variables:

o The density of the population

o Population density affects how often infected, immune and susceptible individuals come into contact with each other. You can change the size of the initial population through the PEOPLE slider.

o Population turnover

o As individuals die, some who die will be infected, some will be susceptible and some will be immune. All the new individuals who are born, replacing those who die, will be susceptible. People may die from the virus, the chances of which are determined by the slider CHANCE-RECOVER, or they may die of old age. In this model, people die of old age at the age of approximately 27 years. Reproduction rate is constant in this model. Each turn, every healthy individual has a chance to reproduce. That chance is set so that each person will on average reproduce four times if they live 27 years.

o Degree of immunity (constant)

o If a person has been infected and recovered, how immune are they to the virus? We often assume that immunity lasts a lifetime and is assured, but in some cases immunity wears off in time and immunity might not be absolutely secure. Nonetheless, in this model, immunity does last forever and is secure.

o Infectiousness (or transmissibility) (variable)

o How easily does the virus spread? Some viruses with which we are familiar spread very easily. Some viruses spread from the smallest contact every time. Others (the HIV virus, which is responsible for AIDS, for example) require significant contact, perhaps many times, before the virus is transmitted. In this model, infectiousness is determined by a slider.

o Duration of infectiousness

o How long is a person infected before they either recover or die? This length of time is essentially the virus’s window of opportunity for transmission to new hosts. In this model, duration of infectiousness is determined by a slider.

How can one experiment?

The factors controlled by the three sliders interact to influence how likely the virus is to thrive in this population. Notice that in all cases, these factors must create a balance in which an adequate number of potential hosts remain available to the virus and in which the virus can adequately access those hosts.

Often there will initially be an explosion of infection since no one in the population is immune and the population density is at its maximum. This approximates the initial “outbreak” of a viral infection in a population, one that often has devastating consequences for the humans concerned. Soon, however, the virus becomes less common as the population dynamics change. What ultimately happens to the virus is determined by the factors controlled the sliders.

Notice that viruses that are too successful at first (infecting almost everyone) may not survive in the long term. Since everyone infected generally dies or becomes immune as a result, the potential number of hosts is often limited. The exception to the above is when the DURATION slider is set so high that population turnover (reproduction) can keep up and provide new hosts.

Examples of real viruses and how their interaction biology affects their spread:

Ebola virus in central Africa has a very short duration, a very high infectiousness value, and an extremely low recovery rate. For all the fear this virus has raised, how successful is it? Set the sliders appropriately and watch what happens.

The HIV virus which causes AIDS, has an extremely long duration, an extremely low recovery rate, but an extremely low infectiousness value. How does a virus with these slider values fare in this model?

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