Lesson Plan for Seventh Grade Life Science
Class period : 53 minutes Mon-Fri, except Tues. 43 minutes
Chapter Seven Genes and DNA
- know that DNA is a component of all living or once living things
- know that DNA can be extracted and observed
California Content Standards Addressed:
7.1 All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
7.1.a. Students know that cells function similarly in all living organisms.
7.1.c. Students know the nucleus is the repository for genetic information in plant and
Materials (per group):
1/2 banana (peeled)
1 zip lock bag
2 plastic cups
1 plastic spoon
1 coffee filter
1 rubber band
ml distilled water
tsp table salt
tsp dish soap
test tubes or jar
1/2 of a banana in a baggie and squish until it is a smooth paste (approx 2
2. In a
beaker prepare extraction solution by combining:
2 teaspoons (10 ml) of soap
1 teaspoons of salt (NaCl)
100 ml distilled water
with a spoon until salt is dissolved - try to avoid creating bubbles in
50 ml or 1/4 cup of the extraction solution (soap/salt solution) to the bag
to gently squish the bag until mixture develops a uniform consistency. Again,
bubbles. (approx. 4 minutes)
a coffee filter over cup and hold in place with rubber band.
banana/soap mixture onto the coffee filter. This will take a few minutes.
ICE COLD isopropyl rubbing alcohol into a test tube filling it about 1/2 full.
2 teaspoons of filtrate and add to the test tube containing alcohol.
to sit for a few minutes and the DNA will slowly precipitate out of
about 5 minutes the DNA will coagulate and can be spooled onto a paper clip
Student Prior Knowledge:
Students should already know:
- DNA can be found in the cells of all living, or once living, things.
- the nucleus of cells contains chromosomes and chromosomes are made up of DNA.
- DNA carries the hereditary information in almost all living things.
- DNA contains the blueprints for the cell and controls the cells functions.
- cells and the nuclei of cells is protected by a membrane composed of lipids.
Students will extract the DNA from cells of a banana using common household ingredients. An extraction solution is used containing soap to dissolve the lipid part of the cell membranes and salt to help the DNA dissolve in the water. Once the DNA is released it can be collected and observed.
1.) What was the purpose for using soap in the extraction fluid?
The DNA is in the nucleus which is protected by a nuclear membrane and the contents of the cell are protected by a cell
membrane. Adding the soap breaks the nuclear and cell membranes, releasing the DNA.
2.) Why is it possible to see the DNA with the naked eye?
A person cannot see a single thread from far away but if there were thousands of threads wound together, it becomes much
more visible. This is analogous to the DNA in this DNA extraction.
3.) Why would scientists want to extract DNA from human cells?
With a pure sample of DNA, scientists can do test newborns for genetic diseases, analyze forensic evidence, study a gene involved
in cancer, or verify a child's paternity.