Science fair projects based on bananas are a great idea because the costs are low and the results can be fascinating. All you need are a few bananas, so parental assistance canl be kept to a minimum. Although each of these projects is described separately, consider performing all four as a larger scale project about the factors in banana ripening.
One experiment that tests the ripeness of bananas is as simple as placing one in a refrigerator. Leave a second banana on a counter and, after a week, compare the two. Although the cold banana's skin will have turned brown, it will still be firm inside. The banana left on the counter, however, will be soft.
Another condition which affects the ripeness of bananas is exposure to air. To observe the effects, place one banana in an air-tight container and compare it each day with a banana left out in the open. For the experiment to be successful, the container must be truly air-tight, such that no air can escape. Ideally, it should be transparent so that you can observe the effects without opening it. After a week, you will observe that the banana in the container ripened more slowly than the one left out in the open.
In addition to air exposure, bananas can also be affected by their proximity to one another. To test this, collect five bananas and three bags. Only one banana should be ripe. In the first bag, place one unripe banana and your single ripe banana. In the second bag, place just one unripe banana. In the third bag, place two unripe bananas. Check the bags each day to observe the conditions of the bananas. You will observe that bag one ripens first. The reason for this is that ripe fruit emits ethylene -- a gas that will increase the ripening of other fruit nearby or, in this case, sharing the same bag. This is why bananas bought on different days should not be kept together.
Light and Dark
In this experiment, the effect of light on the ripening of a banana is observed. One banana should be wrapped in a black bag and placed in a dark cupboard to ensure that no light can reach it. The other should be kept under a lamp, but not so close that the heat of the lamp has any effect on it. The results of this experiment show that exposure to light has no difference on the time it takes for a banana to ripen.