[2026] PTE Academic Reading - Multiple Choice, Multiple Answers

Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere.Since the beginning of the Industrial Revolution, the oceans have absorbed approximately one-third of the CO2 produced by human activities.While this absorption helps mitigate global warming, it fundamentally alters marine chemistry by increasing the concentration of hydrogen ions, which lowers the water's pH.

The most direct consequence of this chemical shift is the depletion of carbonate ions in the seawater.These ions are essential building blocks for calcifying organisms, such as coral reefs, oysters, and certain species of plankton, which rely on them to construct their calcium carbonate shells and skeletons.As carbonate levels drop, it becomes increasingly difficult for these organisms to maintain their structural integrity, leading to slower growth rates and weakened shells.

For coral reefs, the impact of acidification is particularly devastating.Corals must expend significantly more energy to calcify in acidic waters, leaving them more vulnerable to disease, physical damage from storms, and rising ocean temperatures.The degradation of these complex reef ecosystems poses a severe threat to marine biodiversity, as they provide critical habitat and nursery grounds for a vast array of marine species.