Observations and results
The stringy substance that you see is DNA! It has been removed from the millions and millions of cells that make up the banana. All living things have DNA. The more similar and closely related two living things are, the more similar their DNA is. Every human shares 99 percent of his or her DNA with every other person. Furthermore, human DNA is very similar to that of other species. We share most of our genes, which make up DNA, with fellow primates such as chimpanzees and with other mammals such as mice. We even have genes in common with the banana plant!
In this activity each material plays a specific role in helping to extract the DNA from the cells. For instance, the detergent or soap helps to break down the cell's outer membrane, and the salt helps to separate the DNA from other materials in the cell. And because the DNA doesn't dissolve in alcohol, this substance helps the DNA clump together in a separate layer.
Share your banana DNA observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.
You can wash the bag and reuse it. Pour the banana liquid and alcohol down the drain and wash out the cup.
More to explore
"Can Science Save the Banana?" from Scientific American
"Bar Code of Life: DNA tags help classify animals" from Scientific American
DNA model activity from CSIRO's Double Helix Science Club
DNA Interactive site from Cold Spring Harbor Laboratory
My First Book about DNA by Katie Woodard, ages 9–12
Have a Nice DNA by Frances R. Balkwill, ages 9–12
For the Birds: Best-Adapted Beaks
What you'll need
• Cotton swab
• Binder clip
• Several different kinds of seeds, grains or nuts that differ in size and shape. It is best if you have a wide range: some that are tiny (for instance, grass seeds or couscous), some that are medium-sized (black-eyed peas or lentils), and some that are larger (almonds, cashews, walnuts or hazelnuts).
• Timer with a second hand or clock
• Pen or pencil