Science Buddies: "Ask an Expert"

My daughter used one of your science fair project ideas titled Which fruit can ruin your gelatin dessert? Her hypothesis is if I heat up four different types of fresh fruit strawberries, pineapples, bananas, and kiwis then, my gelatin will solidify because when fruit is heated then the protease enzymes are permanently inactivated, making the fruit perfectly fine for making Jell-O. The issue she is having is that the teacher thinks her experiment is not concrete enough or measurable. When she collected her data she made physical observations she also recorded the temperature. She did this for 90 cups of Jell-O every two hours for four hours total. I am thinking that perhaps she needs to modify her hypothesis. How would she do this without losing all the research, data, and results on solidification of gelatin, protease enzymes, states of matter and so forth. She has determined that pineapple and kiwi contain protease enzymes their for ruining your dessert. She also determined her hypothesis was correct. Furthermore, she learned that strawberries and bananas may not be the best choice because strawberries retain water and bananas brown quickly. She also determined that temperature decreases the firmer the gelatin gets. She has so much necessary information and she doesn't know how to fit it all in because of teacher/science fair specifications. She has recommended which fruit she would pick based on all data. Please help! Any suggestions would be greatly appreciated.

Hello, and welcome to Ask an Expert,

Just so we're all on the same page, your daughter is doing this project, correct? (https://www.sciencebuddies.org/science- ... p004.shtml)

Your daughter's hypothesis seems well-reasoned, and it sounds like she has done a very thorough set of experiments, collected lots of data, and drawn reasonable conclusions based on her data. It sounds like a nice science fair project, and I can understand not wanting to have to go back to square one.

Since I haven't talked to her teacher to understand his or her concerns about the project, I can't know this for sure, but I suspect that the teacher is concerned that the project is not quantitative. You can make yes/no observations--did the Jell-O set? Or not?--and that's a valid approach. A lot of science, particularly in the social sciences is done by putting things into categories (e.g., gender, age, eye color, hair color, etc.) These types of things are referred to as categorical variables because they involve putting things in categories. You don't have a number associated with a categorical variable (someone isn't 1.051485 blue eyes, they either have blue eyes or they don't), but you can count how many things fall into a given category (e.g., 23% of people prefer the smell of roses). Other types of variables (e.g., mass, temperature, time) are quantitative variables - they are numbers with units.

While you can't do add, subtract, etc. categorical variables (trying to solve blue eyes + green eyes doesn't make any sense), you can do calculations based on how many things fall into a particular category. So, one thing to consider, if you haven't done so already, is to calculate some percentages based on the data your daughter collected. If you did five different tests of raw pineapple in gelatin and 1 of the 5 samples firmed up, then 20% of the cups with raw pineapple firmed up. You could then make a bar graph comparing the percent of samples that firmed up with different fruits, both raw and cooked. Another option would be to make a graph of how long it took different combinations to solidify.

Those are some thoughts I have based on what you said. If you've already done these things, and your daughter's teacher still has concerns, could you please post the actual text of your daughter's question and hypothesis? Seeing those would help me gauge whether there's a misunderstanding based on how something was written up.

I hope this is helpful; if not, please post back with some more details and we'll do our best to help you and your daughter morph this into a project that satisfies her teacher.

All the best,
Terik

Terik,
I still need some clarification on the hypothesis. If my daughter wrote it like this would it be scientifically correct?
Her new hypothesis Is if I heat up four different types of fresh fruit strawberries, pineapples, bananas, and kiwis then, my gelatin will solidify because solidification occurs as temperature decreases and when fruit is heated then the protease enzymes are permanently inactivated, making the fruit perfectly fine for making Jell-O. If it is not scientifically correct then how would she quantitate her current hypothesis? I greatly appreciate your input.

Thank you,
Tracy

Hi Tracey,

Thanks for posting this hypothesis; it's very helpful. (And I apologize for not picking it out of your first post!)

Your daughter has done a pretty good job of phrasing her hypothesis as an if...then statement. But, it's quite complicated as currently written. I think it would be clearer if she broke it into three parts, perhaps like this: "If I add fresh (insert names of fruit she thinks would prevent Jello from setting) to gelatin, then the gelatin won't solidify when it cools. But, if I add fresh (insert names of fruit she thinks would NOT prevent Jello from setting), then the gelatin will solidify. This is because (fruits she thinks will prevent Jello from setting) have protease enzymes in them, while (fruits that she thinks will NOT prevent Jello from setting) do not. If I heat up (fruits that she thinks will prevent Jello from setting), then the Jello will solidify because the protease enzymes are permanently deactivated." Perhaps reworking the hypothesis in this way will help her teacher better understand what your daughter is testing.

It sounds your daughter is doing experiments that answers two different questions (please correct me if I'm wrong!). (1) Which fresh fruits, when mixed with Jell-O, will prevent the Jell-O from solidifying? (2) Will fruits that stop Jell-O from setting when they are raw still prevent Jell-O from setting when they are cooked? The fact that she is testing two different questions may be part of why her science teacher is concerned, since usually science projects test one question. You can do experiments to explore two different questions as long as appropriate controls are in place. In your case, this would mean that the only difference between Jell-O cups is (1) the type of fruit in the cup (for answering the first question) and (2) raw fruit versus cooked fruit (for answering the second question).

Maybe one way to make this clearer for the teacher would be to explicitly say that this project investigated the answers to two different questions (1 and 2 in the previous paragraph) and two different hypotheses (one about different kinds of raw fruit and a second about raw fruit versus cooked fruit). Perhaps modifying the wording of the procedure to include the word "measure" would be helpful. For example, "Measure the temperature of each cup of Jell-O every __ minutes and record the data in a lab notebook" or "Measure how much the Jell-O has set by wiggling each cup and making notes in a lab notebook".

As a side note, one thing to keep in mind is that while Jell-O does solidify as temperature decreases, solidification happens because of how collagen bonds. Take a look at http://www.scientificamerican.com/artic ... how-does-i.

Let me know if these suggestions make sense or not. We're happy to help in any way that we can!

All the best,
Terik

Hi Tracey,

To add to what Terik said, one quantitative measurements that is possible here is time to solidification instead of just a plus minus measurement of solidification. For example, the sample with no fruit could solidify in 1 hour but a sample with mango could take 3 hours or not solidify at all. The judgement of whether the jello is solid or not is somewhat subjective, but adding a time component will make the experiment more quantitative. All of Terik's adivce is great by the way. There are many possible variables your daughter can test: kind of fruit, amount of fruit, raw vs cooked fruit. These are all valid and she can certainly test more than one variable. The important thing to remember when testing multiple variables is only to change one thing at a time and to always have an appropriate control sample for each experimental variable. I think your daughter needs to decide which variable or perhaps 2 variables she wants to test and then we can help her decide how many conditions and what controls make sense.

Cheers,
Colin