Agriculture and Food 7–12 · Years 11–12
Extracting DNA from split peas
Agri-food, Fibre and Fuel Technologies (HSC elective)
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
The idea
DNA, the material genetic engineering works on, can be released from plant cells with detergent, salt and a protein-digesting enzyme and seen as white strands when it precipitates in cold alcohol.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- isopropyl and ethyl alcohol are highly flammable
- blender blades
- detergent irritates eyes
Controls
- no flames or heat in the room; small volumes dispensed by the teacher
- chill alcohol in an ice bath, never in a domestic refrigerator
- eye protection
- teacher operates the blender
Note
Flammable liquids: NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1 (general information for all staff) and Volume 2 Appendix D (generic risk assessment advice for each chemical). Complete a CSIS or RiskAssess site-specific risk assessment before the lesson.
What you need
- split peas, 100 mL; table salt, less than 1 mL; cold water, 200 mL; blender
- strainer and a measuring jug
- liquid detergent, 30 mL
- meat tenderiser powder (enzyme) or fresh pineapple juice
- test tubes and rack
- 70–95% isopropyl or ethyl alcohol, chilled in an ice bath (not in a domestic refrigerator)
- wooden skewers
How to do it
- Blend the peas, salt and cold water on high for 15 seconds.
- Strain the mixture, add 30 mL of detergent, swirl gently and let it stand for 5 to 10 minutes.
- Pour the mixture into test tubes until each is about one third full.
- Add a pinch of meat tenderiser to each tube and stir very gently.
- Tilt each tube and slowly pour cold alcohol down the side until there is about the same volume of alcohol as pea mixture.
- Watch the boundary between the layers and lift the white strands out on a skewer.
- Extension: predict and then test what happens if the detergent step is left out.
What you should see
White, stringy clumps appear at the boundary between the watery layer and the alcohol within a few minutes and can be wound onto a skewer. As the University of Utah explains, detergent breaks cell and nuclear membranes, the enzyme breaks down proteins, salt helps the DNA clump, and DNA comes out of solution in alcohol. The strands are millions of DNA molecules tangled together with some other cell material, not single molecules. The learner knows it worked when strands collect at the boundary rather than throughout the tube.
What changes
This activity lists no variables to change, measure and keep the same.
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Only animals have DNA.
- The white strands are single DNA molecules.
- Genetically modified foods contain DNA and ordinary foods do not.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
Sources
The pages the author read to write this activity.
- learn.genetics.utah.edu/content/labs/extraction/howto
- www.nsw.gov.au/education-and-training/nesa/curriculum/tas/agriculture-stage-6-2013
- www.nsw.gov.au/sites/default/files/noindex/2025-03/agriculture-amended-st6-syl-2013.doc
- curriculum.nsw.edu.au/learning-areas/tas/agriculture-11-12-2026/outcomes
- education.nsw.gov.au/content/dam/main-education/asset-management/chemical-safety/5._Volume_2_Appendices.pdf