How do Bacteria Use Acids to Spoil Food? — Reading Comprehension

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"This science reading passage, titled 'How Bacteria Use Acids to Spoil Food,' is designed for middle school students to explore the chemical processes behind food spoilage. It aligns with NGSS standards related to matter and its interactions (MS-PS1-1, MS-PS1-2), and matter and energy in organisms (MS-LS1-7). The passage details how bacteria metabolize nutrients, producing acids like lactic and acetic acid, which alter the food's pH, taste, and texture. Key vocabulary terms such as metabolism and pH level are highlighted to build a strong foundation in scientific language. The text also connects this phenomenon to real-world examples, like spoiled milk and fermented foods, and explains common preservation methods like refrigeration and pasteurization. The accompanying multiple-choice questions assess a range of skills from factual recall to application and main idea comprehension."

CONTENT PREVIEW

Bacteria are tiny, single-celled organisms found almost everywhere, including on and in our food. While many bacteria are harmless or even beneficial, some are responsible for food spoilage. This process is often driven by a chemical reaction that produces acids. Bacteria consume the nutrients in food, such as sugars and proteins, for energy. As a byproduct of this process, known as metabolism, they release waste products. In many food-spoiling bacteria, these waste products are various types of acids, including lactic acid and acetic acid.

The production of these acids is the primary reason why food spoils. The presence of a high concentration of acid changes the food's pH level, making it more acidic. This change in pH alters the texture, flavor, and appearance of the food. For example, the sour taste in spoiled milk is caused by lactic acid produced by bacteria breaking down lactose, the sugar in milk. The clumping of milk proteins, which thickens and sours the milk, is also a direct result of this increased acidity. This chemical change makes the food undesirable and unsafe to consume.

This process is not limited to dairy. Other foods, like fruits, vegetables, and even meat, can be spoiled by acid-producing bacteria. For instance, bacteria can ferment sugars in fruit, producing acetic acid (the main component of vinegar) that gives a pungent, sour smell. Understanding this process helps us prevent spoilage through methods like refrigeration, which slows down bacterial metabolism, and pasteurization, which kills existing bacteria.

Fun Fact: Some acid-producing bacteria are intentionally used in food production to create foods like yogurt, cheese, and sauerkraut.

What is the primary reason that bacteria cause food spoilage?

They increase the food's temperature.They introduce air into the food.They produce acids as waste products.They add sugar to the food.

What is the term for the process where bacteria consume nutrients for energy?

DigestionPhotosynthesisMetabolismFermentation

How does the production of acids change the food?

It lowers the food's temperature.It makes the food less acidic.It changes the food's pH level.It removes all bacteria.

According to the passage, what specific substance is responsible for the sour taste in spoiled milk?

Acetic acidLactoseLactic acidProtein

Which of the following is a real-world example of bacterial acid production mentioned in the passage?

The sweet taste of ripe fruit.The clumping of milk proteins.The freezing of water in food.The darkening of a cut apple.

What is the main idea of the reading passage?

Bacteria are always harmful to food.Refrigeration is the only way to prevent food spoilage.Bacteria spoil food by consuming nutrients and producing acids.All sour foods are spoiled.

If a batch of homemade pickles has a very sour, vinegar-like smell, what is the most likely cause, based on the passage?

The presence of lactic acid from bacteria.The pickles were not refrigerated properly.The production of acetic acid by bacteria.The pickles were not sealed correctly.

What is the main purpose of methods like refrigeration and pasteurization, as described in the passage?

To add new flavors to food.To slow down or kill bacteria.To increase the acid level in food.To make food less acidic.