Isolating Plant DNA

Grade Level: 12th Grade
Subject: Biology
Duration: 80 Minutes
Class Size: 20 Students
Curriculum Area: Molecular Biology and Biotechnology
US Education Standards: Next Generation Science Standards (NGSS) HS-LS1-1, HS-LS1-3

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Objectives

1. Understand the process of isolating DNA from various plant sources.
2. Perform DNA isolation using a laboratory experiment.
3. Analyze and perform calculations relating to DNA yield from different plant materials.

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Materials Needed

• Fresh samples of fruits (e.g., strawberries, bananas) and leaves (e.g., spinach)
• Ziplock bags
• Mortar and pestle
• Cheesecloth or coffee filters
• Graduated cylinders
• Test tubes and racks
• Ice-cold ethanol or isopropyl alcohol
• Salt
• Dish soap
• Distilled water
• Measuring spoons
• Thermometer
• Stopwatch or timer
• Lab notebooks
• Gloves and safety goggles
• Permanent markers and labels

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Lesson Outline

Introduction (10 Minutes)

1. Hook: Begin with a brief discussion on the importance of DNA and how scientists use DNA isolation in various fields like forensics, genetics, and biotechnology.
2. Objective Overview: Clarify the goals of today’s lab – students will isolate DNA and perform basic calculations related to their findings.

Pre-Lab Discussion (10 Minutes)

1. Safety Precautions: Highlight the importance of wearing gloves and goggles. Discuss why cold alcohol is used and the purpose of each reagent.
2. Key Concepts:
   • Structure of DNA
   • Cell lysis and why it is necessary
   • Precipitation of DNA

Laboratory Activity (45 Minutes)

1. Preparation and Separation (15 Minutes):

   • Have students work in pairs. Each pair starts by labeling their ziplock bags and test tubes.
   • Place about 50g of their chosen plant material in a ziplock bag and mash it thoroughly with a mortar and pestle.
   • Add 5 mL of water, a pinch of salt, and a few drops of dish soap into the bag. Gently mix without creating excessive foam.

2. Filtration and Extraction (10 Minutes):

   • Filter the mixture through cheesecloth into a test tube, collecting about 10 mL of liquid.
   • Slowly add an equal volume of ice-cold alcohol to the mixture. Observe without shaking.

3. DNA Observation (10 Minutes):

   • Allow the mixture to sit undisturbed. Students will observe the formation of DNA strands at the interface.

4. Data Collection and Cleanup (10 Minutes):

   • Using a stirrer or hook, carefully spool the DNA and set aside in labeled test tubes.
   • Record all observations and measurements in the lab notebook.
   • Ensure all waste is disposed of properly and students clean their workstations.

Post-Lab Analysis (15 Minutes)

1. Calculations:

   • Calculate the volume and possible concentration of DNA obtained from each plant source.
   • Discuss differences in yield between fruits and leafy greens, considering factors such as texture, cellular structure, and water content.

2. Discussion:

   • Reflect on the experiment’s results. Why did certain plants yield more DNA than others?
   • Relate the experiment to real-world biotechnological applications.

Conclusion (5 Minutes)

• Reiterate the significance of DNA isolation and its practical applications.
• Briefly introduce the next topic - genetic engineering and its scientific impacts.

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Assessment

• Lab Notebook: Students will be assessed on the clarity and detail of their observations, data collection, and calculations.
• Participation: Active participation and teamwork during the lab will contribute to their practical skills assessment.
• Discussion: Understanding of post-lab analysis and ability to connect lab activities to theoretical concepts will be evaluated.

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Extensions

• Explore DNA isolation from different biological samples (e.g., animal cells) in a future class for comparative analysis.
• Investigate the role of each reagent used in DNA extraction to enhance understanding of chemical processes.

By guiding students through this hands-on experience, this lesson plan aims to deepen their conceptual understanding of molecular biology and inspire interest in the practical applications of science.