DNA Extraction Lab (Day #2 of 2)

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Students will create and carry out a plan to extract DNA from human saliva (i.e. cheek cells).

Big Idea

All cells contain genetic information in the form of DNA and this incredibly small molecule can be observed before your very eyes! Simply too cool...

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

With regard to this particular lesson...

  1. Students will know that all cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (Emphasis) HS-LS-1 & LS3-1
  2. Students will begin to consider the chemical basis of the Unit’s Essential Question: “What influences your identity and how does it change throughout its lifetime?”
  3. Students will understand that the scale at which DNA works is too small to directly manipulate however it can be observed experimentally.

I hope you get some value from my work!

Anticipatory Set ("Hook")

5 minutes
(Return to Day #1)

Overview of Purpose & Process: Before beginning the lab, I typically like to frame the lab (again for those who may have forgotten a key detail or two or to help students understand a helpful lab technique). Therefore, I review the objective(s) of the lab activity and present and name all equipment for ease of use during lab. This year I added the feature of putting some salt water into the mouthwash (water) to swirl out the cheek cells in order to increase the yield a bit. This is not so pleasant tasting but I think it helps get the most DNA in the end. Lastly, I solicit any questions that students might have prior to starting.

Instructional Input/Student Activities

45 minutes

Teaching Challenge #1: How do I develop routines and procedures to support students to work independently in the science classroom?

Teaching Challenge #2: How can I develop a classroom culture that encourages student engagement, curiosity, and a desire to understand the world through scientific exploration?

As I explained in Part #1, these two interrelated challenges may not be entirely solved or conquered by this activity, however this activity represents several steps along the year-long journey (over which I get to accompany the student) and extending beyond my class. I hope that these experiences build toward a larger sense of independence and curiosity as they become adults.

In particular, I think I can get in the way of students learning by trying to "save them" from every little mishap or explain things to a level of minutiae that is overboard. So in this sense, if students are reasonably mature and have an approved plan then what is my role? I generally sit in one corner of the class in my director's chair for a time to simply watch what is going on. It is very insightful to study the dynamics and hear the conversations that are ongoing. To me this is a cool and authentic measure of true learning. I don't know how aware they are of what I am doing but I'll switch from observe mode to Q & A mode (generally once they are in a groove and have had a chance to start collecting data). So for the duration of the lab I am intentionally playing a minor role (and am available for clarifying questions, to celebrate cool happenings, and be on safety patrol).

With about ten minutes left in class, I direct students to clean up and return to their seats when finished. Those teams that finish early should work to finish the lab write-up, including a picture of their DNA sample!

These two student samples (coded as #1 & #2) show two perspectives on the lab...

Closure: What did we learn? Where do we go from here?

5 minutes

Plus-Minus-Interesting (PMI): As a way to review the process and end result of this cool lab experience, I randomly call on three students to sum things up by sharing their experience through the lens of PMI; in other words self-assessment. 

Typically I get answers like:

(P): "The DNA was really cool and looked like jelly or a cloud."

(M): "The salt in the mouthwash was disgusting!"

(I): "I didn't know that we could actually see the DNA molecule (without a microscope)."