What Causes Ocean Acidification — Reading Comprehension

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Dive into the critical topic of ocean acidification with this comprehensive reading passage. Tailored for science students, the passage explains how the absorption of excess carbon dioxide (CO2) from the atmosphere is changing the chemistry of the ocean. It defines key terms such as pH, carbonic acid, and calcium carbonate in simple language, making complex concepts easy to understand. The passage details the chain of chemical reactions that lead to a decrease in ocean pH and the dire consequences for marine organisms that rely on calcium carbonate to build their shells and skeletons. This resource, aligned with NGSS standards, is designed to enhance student comprehension and critical thinking about this important environmental issue. The included questions are audio-integrated for a richer learning experience.

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A visual representation of the process of ocean acidification. — Excess CO2 from human activity dissolves in the ocean, harming marine life.

Our oceans are massive, covering over 70% of Earth’s surface. They play a vital role in regulating the planet's climate, but they are also facing a major threat: ocean acidification. This is a process where the pH of the ocean water is decreasing, making it more acidic. It is primarily caused by the absorption of excess carbon dioxide (CO2) from the atmosphere.

Since the Industrial Revolution, human activities, such as burning fossil fuels and deforestation, have released enormous amounts of CO2 into the atmosphere. The ocean acts as a huge CO2 "sink," absorbing about one-quarter of the CO2 that we release each year. When CO2 dissolves in seawater, a chemical reaction occurs. The CO2 combines with water (H2O) to form carbonic acid (H2CO3). This carbonic acid then quickly breaks apart, releasing hydrogen ions (H+).

The increase in hydrogen ions (H+) is what makes the ocean more acidic and lowers its pH. This change in pH has a serious impact on marine life, especially organisms that build shells and skeletons out of calcium carbonate (CaCO3), such as corals, clams, and oysters. The higher acidity reduces the availability of carbonate ions, which these animals need to build and maintain their protective structures. It can also cause existing shells to dissolve. This process is a significant challenge for marine ecosystems worldwide.

Fun Fact: The term "acidification" can be misleading because the ocean is still basic on the pH scale (its average pH is around 8.1), but it is becoming less basic, or more acidic, compared to its historical state.

What is the primary cause of ocean acidification?

Volcanic eruptionsAbsorption of carbon dioxideOil spillsUnderwater earthquakes

What term describes the process of the ocean becoming more acidic?

Ocean warmingEutrophicationOcean acidificationCoral bleaching

What substance is formed when carbon dioxide (CO2) dissolves in seawater?

Hydrogen ionsCalcium carbonateCarbonic acidOxygen

How does ocean acidification affect organisms like clams and oysters?

It makes their shells strongerIt helps them grow fasterIt makes it harder for them to build shellsIt increases their food supply

Based on the passage, which human activity contributes to ocean acidification?

Recycling plasticBurning fossil fuelsGrowing vegetablesHiking and camping

Why is the term "acidification" potentially misleading for the ocean's pH?

The ocean's pH is already acidicThe ocean is still basic, just becoming less soThe process happens very quicklyIt only affects certain parts of the ocean

Imagine a scientist discovers a new species of coral that has a skeleton made of a substance other than calcium carbonate. How would this species likely be affected by ocean acidification?

It would thrive in the more acidic waterIt would be unaffected by the change in pHIts skeleton would dissolve, similar to other coralsThe scientist cannot determine the effect without more information

A diver notices that the shells of many snails in a coral reef are unusually thin and brittle. What is the most likely cause, based on the passage?

An increase in ocean temperatureA decrease in ocean acidityA decrease in available calcium carbonateAn increase in fish population