Which chemical is known to influence fruit ripening and flower wilting by signaling hormonal changes?

• A. Ethanol
• B. Acetic acid
• C. Methane
• D. Ethylene

Answer: (D)

Ethylene is a gaseous plant hormone that acts as a signal to initiate fruit ripening and flower senescence. In many fruits, its production rises as they mature, triggering a cascade of changes such as increased respiration, expression of cell-wall–degrading enzymes that soften the fruit, and shifts in color and aroma. It also promotes wilting and abscission in flowers by signaling tissue breakdown at petals and pedicels. This hormone can be produced internally or applied externally to regulate ripening in agriculture. The other substances listed aren’t plant hormones involved in this signaling: ethanol and acetic acid are fermentation byproducts, and methane is a simple hydrocarbon with no signaling role in fruit ripening or flower wilting.