Wait for one hour and watch: What is happening to the scales?
Remove the pinecone and use a towel or a paper towel to dry it.
Insert the closed pinecone into the bottle. If the pinecone doesn’t fit through, use a bottle with a wider mouth or a smaller pinecone.
Wait for a few days for the pinecone to completely dry (speed up this process by putting the bottle in the sun to dry). When the pinecone reopens, it is impossible to take it out of the bottle.
Show the bottle to your family and friends, and watch them as they try to puzzle out how you got the pinecone in the bottle in the first place!
If you can’t find a bottle with a wide enough mouth or a pinecone small and narrow enough to fit through the bottle, perform only the first part of the experiment – soak the pinecone in water and wait for it to close. After it closes, dry it in a microwave. After a few minutes, it will reopen! Important note: do not put the plastic bottle in the microwave!
What’s the science behind this?
Pinecones grow on coniferous trees (such as pine trees) and they have a special ability: they open in hot and dry weather and close in moist and cold weather. This ability is attributed to several factors, most of which are related to the ability of the cone seeds to pollinate, grow new pinecones and protect them.
How do the scales open and close? They are made of wood, which tends to swell when it gets wet or is in a high humidity environment. Wood is mostly made of cellulose, which is a polymer (a large molecule made up of many small molecules linked in a long chain) that can absorb water. When wood gets wet, the small water molecules wedge in between the cellulose chains and push them off each other, making the wood swell.
It is the structure of the scales that enables them to close when they get wet and open when it’s dry. The lower part of each scale has more wood than the upper part and so it moves more - either contracting or expanding the scale.
Some of the scales open only in extremely hot and dry conditions, like those created in a forest fire. Following fires, pinecones open and their seeds, which were kept safe from destruction, fall into the ground, enabling the woods to regenerate in the upcoming winter.