What it shows
Ripening fruits release a gas called ethylene that makes nearby fruit ripen faster. Green bananas sealed with a ripe fruit ripen sooner than bananas left on their own.
The science
Ethylene is a plant hormone that is a gas. Ripe fruits make more of it, and it triggers changes in other fruit: starch turns to sugar, chlorophyll breaks down so the skin turns yellow, and the flesh softens. Enclosing fruit in a bag keeps the gas close to the fruit, so ripening is faster. Fruit in an open place, where the gas spreads away, ripens more slowly. Cold storage slows ripening by reducing the fruit’s activity.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 6 green bananas of the same bunch (or small raw mangoes)
- 1 ripe banana or apple
- Three paper bags or loosely tied plastic bags
- A marker and labels
- A colour chart of 1 to 7 stages (green to brown speckled), which you draw
- A notebook
- A camera or phone for daily photos
Safety
For this project: Wash hands after handling fruit. Do not eat any fruit that smells fermented or has gone mouldy; ask an adult to throw it away.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Label the bags A, B and C and put two green bananas in each.
Add one ripe banana or apple to bag A and close the bag loosely.
Close bag B with just the two green bananas, and leave bag C open on the table with two green bananas beside it.
Place all three in the same room away from direct sun.
Each day at the same time, photograph the bananas and rate the colour of each on your 1 to 7 chart.
Record the daily rating for each in a table, and note the day on which each reached yellow.
Draw a line graph of the average colour stage against the day for the three setups.
Write a conclusion on which setup ripened first and explain it with the idea of ethylene.
What you should see
The bananas sealed with the ripe fruit usually turn yellow first, those in a closed bag alone next, and the open ones last. The graph lines cross the yellow stage on different days.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What gas helps fruit ripen?
Ethylene.
2What kind of chemical is ethylene in plants?
A plant hormone.
3Why did you keep a bag with only green bananas?
As a control, to show what happens without the ripe fruit.
4What changes inside a fruit as it ripens?
Starch turns to sugar, the colour changes and the flesh softens.
Take it further
Compare ripening in a refrigerator and at room temperature, and record how cold changes the speed.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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