Step 4: Project Questions
A science fair project question should identify two variables:
the independent variable
the dependent variable.
Example Questions for the DNA Discovery Investigation
1. The dependent variables are in red type.
This variable can usually be identified from the purpose of the research Discovery Investigation. For the DNA Discovery Investigation, the purpose was to precipitate banana DNA. For your science project, your purpose can be how a change in the independent variable affects the amount of DNA that precipitates.
2. The independent variables are in purple type.
Often, the procedure steps of the research Discovery Investigation gives clues for selecting the independent variables. Examples are shown below:
DNA Discovery Investigation Procedure
Step 1. Peel one ripe banana. Discard the peeling and place the banana in a quart-size resealable plastic bag.
1. What effect does the ripeness of the banana have on the amount of DNA that precipitates
2. What effect does the banana peel have on the amount of DNA that precipitates.
3. What effect does the type of fruit have on the amount of DNA that precipitates.
4. What effect does the type of DNA (animal or plant) have on the amount of DNA that precipitates.
Step 2. Prepare a DNA extracting solution by combining 1/2 cup of distilled water, 1/2 teaspoon of clear dish washing liquid, and 1/2 teaspoon of uniodized table salt.
5. What effect does the amount of water have on the amount of DNA that precipitates.
6. What effect does the type of water have on the amount of DNA that precipitates.
7. What effect does the clarity of the dish washing liquid have on the amount of DNA that precipitates.
8. What effect does the type of dish washing liquid have on the amount of DNA that precipitates.
9. What effect does the amount of the dish washing liquid have on the amount of DNA that precipitates.
10. What effect does the type of table salt have on the amount of DNA that precipitates.
11. What effect does the type of salt have on the amount of DNA that precipitates.
12. What effect does the amount of uniodized table salt have on the amount of DNA that precipitates.
Step 3. Add the extracting solution to the bag with the banana. Seal the plastic bag, and then with your hands, gently squeeze the bag until the contents of the bag is a smooth mush.
What effect does the blending method have on the amount of DNA that precipitates.
Step 4. Filter the banana mixture to separate the residue (solid part collected by filter) from the filtrate (liquid part that drips into the jar). Do this by pouring the banana mixture into a funnel lined with a filter made of two layers of cheese cloth. Collect the filtrate by placing the funnel in a jar.
13. What effect does the filtering method have on the amount of DNA that precipitates.
14. What effect would washing the residue with DNA extracting solution have on the amount of DNA that precipitates.
15. What effect would steeping the mixture before filtering have on the amount of DNA that precipitates. (steep–to let sit in a liquid in order to extract something).
Step 5. When all of the filtrate has collected, discard the residue collected in the cheese cloth.
Step 6. Fill a test tube (a slender jar will work) about one-fourth full with the banana filtrate.
16. What effect does the size of the container have on the amount of DNA that precipitates.
17. What effect does the amount of banana filtrate have on the amount of DNA that precipitates.
Step 7. Tilt the test tube and slowly add about 1/4 test tube of rubbing alcohol. Do not shake the mixture. You do not want the alcohol and aqueous filtrate to mix. (aqueous refers to being mixed with water)
18. What effect does the type of alcohol have on the amount of DNA that precipitates.
19. What effect does the amount of alcohol have on the amount of DNA that precipitates.
20. What effect does mixing the filtrate and alcohol have on the amount of pure DNA that precipitates.
Step 8. Stand the test tube upright.
21. What effect does the position of the test tube have on the amount of DNA that precipitates.
Step 9. Periodically observe the area where the top layer of alcohol touches the layer of banana filtrate. You are looking for a hazy formation –actually the DNA that forms looks like snot. It shouldn’t take more than 5 minutes for the flocculation to occur. (Flocculation means to clump together.)
There are twenty one different example questions and you may have more ideas. Decide on your project question, and then procede to the next step, which is :