Lesson 7

Getting Ready to Explore DNA: Extraction Lab

12 teachers like this lesson
Print Lesson

Objective

SWBAT identify the basic components of DNA and generate questions about DNA to explore further.

Big Idea

Get your students curious about DNA with this question generating lab activity!

Notes for the Teacher

This DNA extraction lab is a classic one!  You can use any grocery item such as onions or peas, but frankly, the color and smell of the strawberry lab is much more appealing to work with.

I use this lesson as a curiosity builder; kids love the procedure of banging the baggies of strawberries and using funnels and other lab equipment.  The directions are very straightforward and there is an explicit connection between the pre-lab summary of information and the analysis questions students are asked to discuss.  The lab does not require a lot of prior knowledge about DNA and generates many content questions and connections both during the session and beyond.

There is a brief question at the end that requires students to dig a bit deeper into the definition of a nucleotide however, overall the goal is provoke interest, generate questions, and enjoy lab procedures that are interactive and related to materials they are already familiar with in their daily lives. 

The Classroom Flow: Introducing the Activity

15 minutes

1.  Tell students that today you will be working on a DNA extraction lab activity. 

2.  Using the spokesperson protocol, ask student lab groups to discuss the following prompts:'

What does the word extraction mean?

How do you think we could extract DNA?

3.  Share out group responses.  Typically students will be able to tell you that to extract something means to take it out.  They will not have a clear idea about how to do that--they will guess that it happens in a lab and that scientists do it with blood samples.  

4.  Tell students that today they will be extracting DNA themselves using simple materials from the grocery store and samples of strawberries for each lab table.  Show students the strawberry DNA extraction materials they will be using.

5.  Pass out the DNA extraction lab document.  Using the popcorn method, read the introduction paragraph and procedure out loud as a class.  Answer any clarifying questions. 

  • Note:  Students will have questions about the amount of material needed in their test tubes.  I typically mark the tubes so that they are looking for about one finger-knuckle's worth of mashed strawberry.  I stress that this test is qualitative, not quantitative and that the exact amounts are not specifically important for our end results.  

The Classroom Flow: Setting up the Experiment

15 minutes

1.  Show students where the materials of the lab are located and the individual lab table equipment set ups they will be using.

2. Ask student groups to assign the following roles:  project manager, clean up and safety, data/observations recorder, and research librarian.  

  • Note:  You may have other roles you typically use in your classroom; use whatever feels most appropriate for your students.  At this point in the year, I don't tend to assign the roles but rather, offer them as a suggestion for groups to use as they plan their own strategy to meet the lab  activity expectations.  If there are any groups that need additional support, I work with them individually to create and assign appropriate roles within the team structure.

 

3.  Once student groups have determined their individual roles for the lab activity and their overall plan, they may move to their lab tables and begin their activity.

4.  This will be a noisy time for the first ten minutes of class as students bang on their baggies to pulverize their strawberry samples and enjoy the science play aspect of this lab procedure.  

5.  This section of the lab activity is busy and may require your assistance as students determine the right technique to use as well as work with their funnel apparatus.  Overall, you will find students will be engaged and productively busy.

  • Note:  Students will need to be reminded that they want all of their strawberry mash to go through their napkin/filter so that only the liquid portion winds up in the test tube while the seeds and pulp stay in the funnel.  The best way to smash strawberries is a rounded motion with the palm rather than a banging of the baggie on the table--that will result in holes in the baggie which simply lead to spills.  

6.  You will see many examples of productive, on task collaborative work throughout this engaging session:

  • Students will collaborate to read and understanding this multi-step procedure.
  • Students will get materials and explain their use to team members.
  • Students will look up DNA diagrams in their textbook for group discussion.
  • Students will help each other see the DNA in the tube.
  • Students will share their DNA extraction funnel set up with other groups.
  • Students will show other groups their extracted DNA for comparison.
  • Students will clean up their lab tables and materials together.
  • Students will discuss their lab analysis questions and confirm their conclusions.

The Classroom Flow: Lab Observations and Reflections

15 minutes

1.  Students will settle into a quieter space as they observe their funnels and wait for their samples to be ready for extraction.  There will be three basic phases:  

  • The careful layering of the strawberry mixture and the alcohol
  • The insertion of the glass stirrer into the middle layer where the DNA is located
  • The slow extraction of the DNA out of the tube

 

2.  Once students begin extracting their DNA, be on hand to encourage and congratulate!  The kids love that type of feedback from their teachers especially during lab situations.  It is a great opportunity to build community and connections as you share a common interest and collaborate to accomplish a task.

3. As students begin to clean up their materials and return to their lab tables to work on their analysis questions, remind students that they can be working on their lab observation/analysis questions as a team or looking up nucleotide definitions and diagrams in preparation for the last question on the lab document.

The Classroom Flow: Generating Questions

10 minutes

1. With the remaining time, ask student groups to think of one big question they have about DNA and list it on the board for public viewing.  Some potential student questions include:

How do scientists figure out what genes are on each chromosome?

Can scientists take out or add in genes to cure diseases?

How does DNA get mutated?

  • Note:  I like to keep each class period's work up on the board for everyone to see and comment upon throughout the day.  I also type out or photograph their board responses to use later on throughout the unit as a check-in for myself as a teacher to ensure that we have working through student interest-based questions relevant to our topic either as a group or on a small group or one-on-one basis.  

2.  Let students know that this is an important unit of study that we will be spending a lot of our time on and that our goal is to explore all of their questions together as a team! 

3.  Check out this example of student work for this activity.  Students should be able to summarize the purpose of each material use in the extraction technique and to draw a detailed drawing of a segment of DNA.