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Dec. 03, 2010

Science Dad on Why Fruit Continues to Ripen

by Vince Harriman

Click to enlarge images

Getting ready for Thanksgiving last week, Beckett and I noticed that our Hallowe'en pumpkins had ripened considerably since we first bought them. We decided to come up with an experiment to see if we could figure out some of what goes on after fruit and vegetables are picked. My goal for this project was for Beckett to learn a little bit about the scientific method: observation, collection of data, as well as organizing and understanding what we were seeing and learning. Since we didn't have room for dozens of giant pumpkins in the house, we decided to use bananas. Here is what we did.

Bananas numbered and green!

We went shopping together and found the six greenest bananas we could find. We divided the bananas into three groups and numbered them from one to six. The first two bananas we would leave exposed to open air (Group 1) with an apple. The second two bananas (Group 2) were vacuum sealed in a bag with an apple. And the last two bananas (Group 3) we placed in a paper bag with and apple and folded over the top. The idea was to see what happened with bananas in open air, with no air whatsoever, and with air restricted. After Beckett labeled and assembled the three groups we photographed each set. They were all uniformly green and hard as a rock. We put them aside. We decided to check on them every twenty four hours and note what happened.

Day 2: Group 1
Day 2: Group 2
Day 2: Group 3
Day 4: Group 1
Day 4: Group 2

On the first day there was little change to any of the bananas. The group in open air and the group in the paper bag had lost just a bit of their green and were just a tiny bit softer. The vacuum group was still very green and hard.

We took photos of each and I helped Beckett create his first 'lab notebook'. The notes were short and to the point, but as he learned on subsequent nights, his memory could not be trusted to remember which bananas had changed. This is what a scientist would call data -- a set of observations about something that we could refer to later and use to draw our conclusions.

On the second day we began by trying to remember what we had observed the day before. Then we inspected our three groups and took notes. The group in open air (Group 1) was now yellowing nicely, the group in the paper bag (Group 3) was changing, and the group in the vacuum seal (Group 2) was as green as can be. We compared our memory to our notes and decided that 'data' and lab notebooks were excellent tools for scientists.

Enjoying the experiment!

On the third day we observed quantitative as well as qualitative progress. Beckett wrote down that the bananas from Group 1 were yellow with 1/4 of the tip green, the bananas from Group 3 were yellow with 1/2 tip green, and the bananas in the vacuum were as green as the first day. Interesting results!

By the fourth day, the first and third groups were yellow with hints of brown. It was time to eat them. I had Beckett create a second set of data -- qualitative. In this case, we would eat bananas from all three groups and rate them for sweetness, firmness, and overall 'yummy-ness'. We had seen what the three scenarios did to the outside of the bananas, now it was time to see what it did to the inside. Surprisingly, Beckett chose a banana from the vacuum seal -- the least ripe and firmest bananas -- as his favorite.

I asked him to form a hypothesis to explain what was going on and without hesitating he said that air was somehow a factor in how fruit ripened. This was a great experiment which taught us a lot about using scientific methods to learn from what we see. We learned how to take and record two kinds of data (three, counting the photo documentation) and form a theory from our hypothesis and data.

We did some research and found out that most plants produce something called ethylene (two atoms of carbon bonded to four atoms of hydrogen) that governs the ripening of fruits and vegetables. It even plays a role in plants shedding leaves -- I don't know why we didn't find out about it when we did our leaf project! It turns out that even Ancient Egyptians and Chinese among others knew something about ethylene -- even if they only knew as much as we had just discovered with our experiment.

We cleaned up the mess we made of the counter and put away our new lab notebook. Looking over our lab notes and photos, we used the data collected and with our hypothesis formed a theory -- fruit needs air to ripen, and ethylene too.

And then we ate the bananas!

About Vince Harriman

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 and Rowan-2 1/2 ask him 'why' approximately 6,542 times a day.

The views expressed are those of the author and are not necessarily those of Science Friday.

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