Editing PH (section)

=== pH in plants ===
[[File:Lemon_-_whole_and_split.jpg|thumb|[[Lemon juice]] tastes sour because it contains 5% to 6% [[citric acid]] and has a pH of 2.2 (high acidity).]]
Plants contain pH-dependent [[Plant pigment|pigments]] that can be used as [[PH indicator|pH indicators]], such as those found in [[hibiscus]], [[red cabbage]] ([[anthocyanin]]), and grapes ([[red wine]]). [[Citrus]] fruits have acidic juice primarily due to the presence of [[citric acid]], while other [[Carboxylic acid|carboxylic acids]] can be found in various living systems. The [[protonation]] state of [[phosphate]] derivatives, including [[Adenosine triphosphate|ATP]], is pH-dependent. [[Hemoglobin]], an oxygen-transport enzyme, is also affected by pH in a phenomenon known as the [[Root effect]].