Connecting to Chemistry
In general chemistry we spend a lot of time talking about atoms and what makes them either stable or unstable. Just like humans, atoms want to use the smallest amount of energy possible. In order to accomplish this they tend to form bonds with other atoms to form molecules or formula units. Atoms can either transfer or share electrons in addition to being attracted to opposite charges. In general scientists refer to atoms bonding ionically, covalently, or forming hydrogen bonds. When forming ionic bonds electrons are either given away or taken from another atom. Certain atoms, specifically metals, prefer to donate their outer shell electrons, valence electrons, in order to obtain a pseudo-noble gas configuration. Unlike metals, nonmetals tend to have more valence electrons and prefer to gain extra electrons becoming negatively charged in order to attain a pseudo-noble gas configuration. Atoms are willing to gain or lose electrons to become similar to noble gases because they are the most stable due to having a full octet, or 8 electrons in their outer shell. When an atom has a full outer shell it is most stable and no longer wants to gain or lose electrons.
After atoms have bonded they are no longer transferring electrons but are still subject to the electrostatic forces between their subatomic particles. Each element is assigned a numerical value to represent how badly they want another electron in their outer shell, which we refer to as their electronegativities. Metals tend to have low electronegativities representing how easily they are willing to give up their valence electrons, whereas nonmetals have higher electronegativities because they are closer to having a full octet so they gain extra electrons. It would be simpler if all atoms either gained or lost electrons, but that is not the case. If two atoms are in the same vicinity and want to bond because the nucleus of one is attracted to the electron cloud of the other, it is not necessarily the case that they can bond ionically. If the atoms have similar electronegativities they end up sharing their valence electrons so that each atom has a complete octet some of the time. Just like when two siblings are responsible for sharing a vehicle, there is usually one who is stronger, more electronegative, than the other, and that atom will obtain the shared electrons more often than the weaker atom.
Once atoms have bonded they do have lower energies and are more stable, but are not necessarily done acting or reacting to the other atoms or molecules around them. Keep in mind that all of these electrostatic charges around each other will not be ignored. In ionic compounds the ions come together to form crystal structures nicely aligning the positive and negative charges evenly forming a strong stable crystal structures. When atoms bond covalently instead they have to share the electrons creating dipoles or partial charges within molecules. Bonds are labeled as polar when the electrons are pulled more in one direction, towards the more electronegative atom, than another. When a molecule has multiple atoms the bonds between those atoms can either cancel out their polarities or overall pull the electrons more in one direction than any other resulting in a polar molecule. Similar to how ionic compounds line up their cations (positively charged atoms) and anions (negatively charged atoms) the dipoles within covalently bonded molecules align themselves as well.
After atoms have formed compounds they may still change again in order to become more stable in a chemical reaction. In general chemistry we tend to discuss combination, decomposition, single replacement, double replacement, and combustion reactions. The overarching idea to keep in mind is that in a chemical reaction atoms just rearrange. When teaching chemistry we are always trying to get students to think at the atomic or molecular level and to think about the interactions and reasons why changes occur.
Previously I alluded to cations and anions, but there are also polyatomic ions which are a small group of atoms covalently bonded but acting as a group which has a net charge. Traditionally general chemistry classes only talk about the most basic molecules but this may be preventing students from pursuing their curiosity about the chemical reactions that happen within our own bodies and in the foods that we eat. If we specifically think about DNA (or deoxyribonucleic acid) the same forces that bring atoms and molecules together make our DNA align itself into a specific structure or shape. DNA is composed of two strings of long molecules covalently bonded together; the two strings are additionally connected by hydrogen bonds creating a double helix matrix of molecules. Keep in mind that the forces bringing these molecules together are those same positive and negative charges originally bringing together ions to form ionic bonds.
Our DNA defines us as humans. These simple chemistry concepts work together in the formation of DNA. DNA is a double stranded polymer where there are two rails which are covalently bonded then becomes more stable when hydrogen bonds are created between the two rails. There are four monomers which are involved in the coding of our DNA; these monomers are adenine, thymine, cytosine, and guanine. These monomers always partner in a specific way, adenine always pairs with thymine, and cytosine always pairs with guanine. The order of these pairs determines the traits that our genes express.
If you are trying to give a plant a heartier root stock, you would need to know where to find the DNA of the plant cell and more specifically what part of the sequence when activated determines how the roots grow. Plant cells are different from animal cells in that they have a rigid cell wall which is harder to get through than a cell membrane. When looking at the rails of the ladder or the backbone of the DNA polymer we notice that the molecules have aligned themselves so that you see ribose then a phosphate in a repeating pattern as shown in the picture.
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In order to genetically modify plants scientists must first identify which characteristics in a plant they want to modify. This is also important because the new sequence to be inserted must be able to travel into the nucleus where the plant DNA is found. In order to make pieces of DNA small enough to use scientists use plasmids which are small circular pieces of DNA. A restriction enzyme is used to cut the DNA into small pieces. Once the plasmid containing the desired gene is isolated scientists add a promoter, the desired gene sequence, and a terminator to the original sequence. The new sequence is then inserted back into the organism where the promoter initiates transcription for the new DNA sequence.
Scientists can actually change the DNA sequence by cutting the original chain and sending in a new sequence to modify the gene, which can then be expressed in its new form. Just like how H 2O, water, and H 2O 2, hydrogen peroxide, are made of the same pieces, having one extra particle makes a huge difference and completely changes the properties of that molecule. After identifying the part of the sequence that determines root properties the scientist would insert a replacement sequence with the DNA sequence from another plant with the desired property or a synthetic version of the desired sequence.
Differences in the genetic sequence will modify the characteristic of the plant's genome. When replacing an original section of DNA with a new sequence I am reminded of a single replacement reaction where you are literally replacing one element or polyatomic ion with a different one in order to change the properties. I think this mechanism clearly relates the two procedures even though the levels of complexity are removed from this scenario.
Strategies:
Students will begin by creating a concept map of their perception of what makes them who they are while thinking specifically as a scientist. I expect answers to vary and that many concept maps will include items such as their personality, style, environment, experiences, food, biology and chemistry. Students will then find an elbow partner to see if they have any similarities or differences. This will lead to the class charting what they feel are the most important items from their charts. The discussion will be guided towards thinking about the foods we eat, and the biology and chemistry behind it.
Students will be reading articles emphasizing the pros and cons of genetically modified crops and then they will interact with several case studies from the National Center for Case Studies. Students will work through two case studies one called Frankenfoods and the other called Tougher Plants 11. These two case studies were specifically chosen to ensure that both the pros and cons of genetically modifying plants are thought about. Each case study will have students working in diverse groups in order to encourage conversations between students with varied home lives. Students will then work with their groups to create a chart of all factors they believe should be considered when deciding if crops should continue to be genetically modified or not.
The positive effects of genetically modifying plants that they will be presented with are needing less water to grow, using less chemicals to keep crops healthy, higher production rates, more aesthetically pleasing, higher nutritional values, and allowing farmers a larger profit margin.
On the other side the negative effects will include higher produce prices for those who choose to eat non-modified produce, have a different taste, the creation of superbugs, unintentional contamination of non-modified foods, lack of labeling regulations, creating new allergens, and the loss of biodiversity. The fact is that no one knows what the results of continuing to create genetically modified plants will be. There are some very valid concerns especially when the original intent of the created plants causes more problems than expected.
The final article students will be given before the trip to the farm will be "GMO Crops Mean More Herbicide, Not Less" written by Beth Hoffman for Forbes Magazine. This articles states that the corn and soybeans being planted were genetically modified to withstand herbicides; however, there are two recent studies showing that the reduction in herbicide use only lasted a few years. After the first few years the amount of herbicides being used multiplied seven fold. This in fact does not lead to the farmer making money but again costs the farmer more to produce the crops which in the end cause consumers to pay more at the grocery store. In this particular case the only people making money are the companies producing the genetically modified seeds and the companies providing the herbicides. Along with needing more chemicals to treat crops to ensure production there are also many articles cautioning about the emergence of superbugs. Nature still follows the survival of the fittest mantra, so if crops become resistant to a certain pest, those pests will evolve to come at the crops in another way.
Since many city students have never had a garden nor have family members with a garden I find it necessary for them to actually see the growth of zucchini plants that have been genetically modified as well as the growth of non-modified zucchini. Activity 3 is given as one example of a data collection chart for students to use as a template. They will need to create their own chart and determine what characteristics of the plants and zucchini they deem important. I expect that some students will choose to find the mass of the zucchini produced where as others will focus on aesthetics of the plants and products. It is imperative that they be very clear on how to monitor the experiment to make sure that the plants are given the same opportunities to grow. As with any experiment using the scientific method they need to identify one and only one variable, in this case it is the seeds being modified or not. The data collected will be useless if the other conditions of the experiment are not kept the same.
Students will also be asked to collect data to compare genetically modified zucchini to non-GMO zucchini. This data is to be considered when creating their position paper and used as evidence to back up their thoughts. Students will also be asked to reflect on whether their opinion has changed throughout the unit and what changed their minds. I would like them to collect data on the plants, the number of zucchini produced, and the sizes and quality of the products. Students will also have an opportunity to determine if they can differentiate between the tastes of the products. Students will also have access to records of the pesticides and herbicides used, if any.
I would like students to identify how many GM products they consume and what steps they can take to predict how much they are exposed to GMO's. If students can raise enough money to pay for a bus, we will take a field trip to Orton's Fruit Farm in North East Pennsylvania where students will be able to see how fields are planted and ask questions about how GM crops have affected small farm owners. The experts in this case will be my father and brothers, who currently run a hundred acre farm. The farm is currently used to grow 75 acres of apples, 15 acres of grapes, and 10 acres of various vegetables, all to be sold on fresh market. Students will be shown how crops are treated with herbicides and pesticides, and see the damage to crops when not treated. I also think it is important for them to realize that farmers do not have an income if they have no crops to sell, so if the produce is small, ugly, or bruised the farmer's income is greatly diminished.
At the farm, my brothers Matt, Mike, and Mark pull out the different equipment used to prepare the soil, till it, and maintain growth including the use of herbicides and pesticides. There is a very detailed process of keeping track of how much chemical is being used and where it is being used. There are classes that farmers must attend and tests they must pass in order to have the right to use these chemicals. Just like teachers have to have continuing education credits, so do farmers. My brothers will also explain the need for irrigation and show how the pipes are moved in order to rotate which crops are being watered and when.
Students will inevitable ask questions like why they are not irrigating during the day when the sun is out. Plants are not watered during the day because the water is drawn out of the leaves too quickly and the leaves burn, so they get watered either early in the morning or in the evening. The first time I took students to the farm we showed them several man-made ponds used for irrigation and they were amazed at how I grew up with a lake on our property. Since this is a huge misconception that I did not anticipate, the next time I took students to the farm we also made a stop at Lake Erie which is only 2 miles North of the farm. I explained that Canada is only 40 miles on the other side of the lake and kids I went to high school with swim it each year. Students were in awe and asked if they were at the ocean. I had always taken my life experiences for granted and had no idea how not growing up around an actual lake throws what we learn early on in geography class out of proportion. The students had this awesome new experience and shared that with their friends once we returned home. My hope is to again incorporate a trip to the farm so that they can see the differences in the crops.
My parents also have a fresh market store and a wholesale business where students will see where fruits and vegetables are stored prior to arriving at a grocery store. While on the farm we feed them and they can taste the difference between having fresh fruits and vegetables compared to the imported fruits that are picked weeks early so that they can travel to the grocery stores where they are sold with limited damage since they are not ripe. My students never understood why I said I would not purchase fruits like apples and peaches from a grocery store until they tasted the difference for themselves. Even three years after I took the first group of students to the farm, I saw an old student at a Pirates baseball game and he asked me if I had any apples. This touched my heart because I knew I shared an experience that will never be forgotten.
After visiting the farm and getting a clearer vision of agricultural practices students will have another article to read, and then will need to put together a position paper. In order to help students organize their thoughts I have them use the claim-evidence-reasoning model in science. Students tend to get bogged down when reading non-fiction and get confused about what to do with the text. I find posing a question for them to specifically answer helps them write as if they are telling another person why they believe they have the correct idea. It is not my concern about which claim they make, I am more interested that they make an appropriate claim and choose evidence that actually backs up the specific claim that they are trying to prove. I consistently find myself telling my students that if they were scientists they would always be trying to prove something and no one is going to believe them just because they say something. Once students have put together a few scientific explanations they tend to do very well with both the claim and listing appropriate evidence, but struggle with the reasoning. I feel the reasoning is the most important part; this is the thought behind why you chose that specific piece of evidence to support your claim. I think that if you have a personal stake in what you are writing about or explaining that you make a more compelling argument. This is an additional reason I chose to pose a question that directly relates to the everyday lives of my students. I don't think it gets more personal than thinking about the foods you put into your body and the implications of how our lives can be changed by the recombination of tiny molecules.
Activity 1: Concept Map
Directions: Thinking like a scientist what is it that makes you who you are? Be specific and make connections where you feel there are overlaps. Add more lines as needed.
Activity 2: Create a list of the pros and cons of using genetically modified crops then decide if you are for or against the continuation of genetically modifying crops. You will use this list for another assignment.
Make a claim that you will defend in a position paper. Your claim will be the beginning of your scientific explanation. Your position paper will begin with a claim, then you will add evidence from the texts you have been reading, and then explain why the evidence you chose backs up your claim.
Sample Claim: Eating fresh fruit is a healthier choice than snacking on a candy bar.
Claim:
Activity 3: Sample Data Collection Template
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