The climacteric is a stage of fruit ripening associated with increased ethylene production and a rise in cellular respiration. Apples, bananas, melons, apricots, tomatoes (among others) are climacteric fruit. Citrus, grapes, strawberries are non-climacteric (they ripen without ethylene and respiration bursts). However, there are non-climacteric melons and apricots, and grapes and strawberries harbour several ethylene receptors which are active. Climacteric is the final physiological process that marks the end of fruit maturation and the beginning of fruit senescence. Its defining point is the sudden rise in respiration of the fruit and normally takes place without any external influences. After the climacteric period, respiration rates (noted by carbon dioxide production) return to or below the point before the event. The climacteric event also leads to other changes in the fruit including pigmentchanges and sugar release. For those fruits raised as food the climacteric event marks the peak of edible ripeness, with fruits having the best taste and texture for consumption. After the event fruits are more susceptible to fungal invasion and begin to degrade with cell death.