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Name: Mia
Status: student
Grade: 12+
Location: N/A
Country: Norway
Date: Summer 2011

I read the question about pine cones wet and dry. My question is : what is the structural mechanism in detail, that is at the origin of opening and closing ?

You might want to look into it as a result of the ripening and breakdown (oxidation and decomposition) of the fruit.

Anthony Brach
Missouri Botanical Garden
c/o Harvard University Herbaria

Weight loss of a ripening banana is correlated with its ripening, not the cause. Look at what is going on. Ethylene gas is released by the chemical reactions involved in the ripening process. This results in a slight weight loss. More importantly, the banana skin and the inside of the banana become softer and more permeable to water loss.

The ripening process also releases other chemicals into the air. You can smell the volatile compounds. All of the evaporations result in weight loss, which is a consequence of the ripening process.

Vince Calder

Both! Banana is one of many fruits that undergo ripening. Ripening is a physiological maturation catalyzed by the plant hormone ethylene (C2H4). Ethylene starts a cascade of reactions leading to a respiratory climacteric (basically a brief but significant spike in respiration). Carbohydrates are used as substrate, hence the decrease in weight. Thus there is a direct correlation between weight loss and ripening.

However, weight loss is also a cause of the ripening process. During the climacteric, ethylene is produced in situ as one product of respiration. This induces the production of more ethylene, which further ratchets up the process.

Dr. Tim Durham
Instructor, Office of Curriculum and Instruction University Colloquium
Department of Biological Sciences Florida Gulf Coast University

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