Strawberry DNA Extraction
Lesson 5 of 14
Objective: SWBAT utilize everyday materials to extract and view DNA from a strawberry.
As the students enter the room, they take out their journals and respond to the prompt: Think about the online DNA extraction. Describe the process and the equipment used in the simulation.
As the students work on the prompt, I circulate through the room to review their answers. Once the students have had an opportunity to record their thoughts, I ask for a volunteer to explain the first step in the extraction process. From there I ask the students follow up questions, such as why cheek cells are used in the extraction process. I continue asking questions until we have reviewed all of the steps and the equipment used in the online extraction.
The students take out their Chromebooks and log in to Classroom on Google. While they do this, I use the SMARTBoard to display the NIH National Human Genome Research Institute project link for the lab instructions. I highlight areas of the materials and procedures list that the students will modify for this lab. For instance, I have the students use a mortar and pestle instead of a plastic bag to smash the strawberry. We also use beakers instead of plastic cups. Additionally, I point out that while salt is not listed on the materials list, it is used to make the buffer solution. As we review the instructions, I ask the students if they have any questions about the procedures or the process.
Before the students are placed into groups for the lab, I remind them of the safety rules and explain that they need to wear their aprons and goggles. This lab does not include harmful chemicals, but I have found that it is easier to have students develop the habit of wearing their aprons and goggles. I also stress the importance of not eating in the lab, as strawberries can be very tempting.
Once we have reviewed the instructions, the students go to the lab. One student from each group is responsible for taking their Chromebook, so the instructions can be accessed and the accompanying questions can be completed.
After all of the students have their aprons and goggles on, I ask them to have a seat and then we make the buffer together as a class. I ask the students to read the amounts for each ingredient and then I have one student put in each of the different ingredients. I quickly review the modifications we have made to the lab instructions, and I remind the students to complete the Strawberry DNA Extraction Questions once they have finished with the lab.
These videos represent the students' favorite part of the lab and are two steps that I generally warn them about. When smashing strawberries, the students need to be careful not to spill the juice. The students also need to be careful when filtering juice, so the coffee filter does not rip.
While the students are working on the activity, I circulate through the room, checking to ensure that they are correctly following the procedure. I also spend time asking the students about the steps they are completing. I regularly ask the students why they are completing a certain step. For instance, I ask them to explain why the directions have them remove the stem from the strawberry.
This is a student work sample. The students had difficulty answering some of the questions because some of the information, such as the composition of the cell membrane and the definition of osmosis were items we had covered in previous units. Some of the students also had difficulty extending their thinking beyond the visuals of the lab. We reviewed and discussed the answers to these questions as a class, to help ensure student understanding of the concepts.
While the students work on the lab, CCSS RST.6-8.3 is addressed. The completion of the lab, following the online exploration, helps to lay the foundation for NGSS MS-LS-3 as students begin to understand the role that DNA plays within the cell and within the organism.
At the end of class, I ask the students whether they preferred the online extraction or the hands on lab. For the most part, students preferred the hands on lab because they were able to touch the materials. The students also said they felt it was helpful to have completed the online extraction prior to completing the strawberry DNA extraction.