Using bananas, test how different temperatures and environmental conditions affect the ripening speed of bananas.
Why use bananas?
- can be bought unripe and will ripen
- visible change in ripening
Independent variable is the environment, since it is not dependent on anything but the experiment (we’re not going to conduct this outside).
Dependent variable is the ripening speed of the bananas, because this is changing based on the environment.
Bananas, as most people know, are yellow when ripe and have a soft yellow flesh that is sweet. They can ripen independently from their plant, as can be seen when you buy a green one and leave it on your counter. Like other fruits, there are factors which influence the speed at which they ripen. A major factor influencing the ripening speed of fruit is the presence of ethylene.
Ethylene is a hormone produced by most fruits; it is a colorless gas with the chemical formula H2C=CH2 (the carbons are double-bonded). Ethylene is lighter than air, which makes it diffuse rather rapidly. When a fruit is exposed to ethylene, it ripens at speeds faster than it would without. Oxygen is necessary for this reaction as well. Every fruit reacts differently to ethylene; bananas are heavily affected by it, while most berries are not.
Of course, there are obviously other factors which influence the speed at which all fruit ripen, e.g. disease, temperature, light exposure…
If you place a banana in a warm environment with large amounts of ethylene gas, then the banana will ripen faster.
- 7 unripe (green) bananas – NOT baby bananas or plantains
- a refrigerator or other cool (1 to 6°C) place
- a freezer (-10 to -2°C)
- two plastic bags (not airtight)
- two ripe or half-ripe apples
- a large closeable (not airtight) cardboard box
- Make sure all bananas are about equally unripe; if there is a significant difference between any two, then get new bananas.
- Take one banana. Look it at, note the color, peel it, and take a bite; record the taste (the sweetness) in your data table. Feel the banana; is it hard and firm or soft and mushy?
- Place one banana under normal conditions. This means somewhere around room temperature, good light exposure, on the kitchen counter or some similar place. This will act as the control.
- Place one banana in the refrigerator, away from any clutter (e.g. eggs, parsley, oranges…)
- Place one banana in the freezer, again away from clutter
- Place one banana in each plastic bag. Close one off so that not much oxygen gets in, but make sure to leave a connection with the outside world. In the other bag, place the two apples and close it off like you did with th first.
- Place one banana into the box and close the box, to make that banana in relative darkness compared to the control
- Wait two days, then remove each banana from its environment, making a careful note of where each one came from
- Perform Step 2 with each banana; observe it, taste it and feel it, and record it in your data table.
Note: Do not taste a banana with brown flesh – it is rotten and overripe.
Dispose of the bananas after the experiment.