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Digestive System — Reading Comprehension

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MS-LS1-3
MS-LS1-7

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This comprehensive science passage for grades 6-8 explores the digestive system, tracing the step-by-step journey of food through the human body. Aligned with NGSS standards MS-LS1-3 and MS-LS1-7, students discover how food is broken down in the mouth, stomach, and intestines, and how nutrients are absorbed for energy production. The passage explains the role of organs like the liver, pancreas, and gallbladder, integrates key vocabulary, and connects digestion to the broader concept of cellular respiration. With audio support, Spanish translation, quizzes, writing prompts, and graphic organizers, this resource is ideal for diverse learners in middle school science classrooms. Key concepts are reinforced through activities and accessible explanations, making it perfect for teaching body systems and life science.

CONTENT PREVIEW

Digestion is the process by which the body changes food into substances it can use for energy, growth, and repair. When a person eats, the food must be broken down into smaller molecules that can be absorbed and delivered to cells. The digestive system is a complex network of organs and specialized chemicals that work together to accomplish this task. Understanding how the digestive system functions reveals how our bodies extract nutrients and energy from what we eat—and why this process is essential for life.

Mouth to Stomach: The Start of Digestion

The journey of food begins in the mouth, where both mechanical digestion and chemical digestion occur. Teeth break food into smaller pieces (mechanical), while saliva, containing enzymes, starts to break down carbohydrates (chemical). The chewed food, now called a bolus, moves to the esophagus. Muscular contractions called peristalsis push the food toward the stomach. In the stomach, powerful gastric acid and digestive enzymes further break down proteins, turning the mixture into a semi-liquid called chyme. The stomach’s strong muscles churn the food, increasing the efficiency of chemical breakdown. On average, food spends 2-4 hours in the stomach.

Small Intestine: Absorption of Nutrients

Chyme enters the small intestine, which is over 6 meters long in adults. Here, most nutrient absorption takes place. The small intestine is lined with millions of tiny fingerlike structures called villi, which increase the surface area for absorption. Accessory organs—the liver, pancreas, and gallbladder—release substances that help digestion: bile from the liver breaks down fats, pancreatic enzymes digest proteins, fats, and carbohydrates, and the gallbladder stores and releases bile as needed. Nutrients like glucose, amino acids, and fatty acids pass through villi into the bloodstream. About 90% of nutrient absorption occurs in the small intestine.

Large Intestine and Beyond: Water Absorption and Waste Removal

After leaving the small intestine, indigestible food material moves into the large intestine. Here, water and minerals are absorbed, and the remaining material is turned into solid waste called feces. Helpful bacteria in the large intestine also produce some vitamins. Waste is stored in the rectum and eliminated through the anus. The end result of digestion is that nutrients are delivered to cells, where they are used in cellular respiration to create energy the body needs for all activities. This connection between digestion and cellular respiration is why eating is vital for survival.

Modern science has uncovered the details of digestion through experiments, technological advances like endoscopy, and biochemical analysis. Understanding the digestive system helps doctors treat illnesses, improve nutrition, and develop new food technologies.

Interesting Fact:
The surface area of the small intestine, thanks to villi and microvilli, is about the size of a tennis court—allowing maximum absorption of nutrients!

What is the main function of the digestive system?

To break down food and absorb nutrientsTo pump blood throughout the bodyTo protect the body from germsTo control body movements

Which organ releases bile to help break down fats?

PancreasLiverStomachEsophagus

Where does most nutrient absorption occur in the digestive system?

MouthStomachSmall intestineLarge intestine

What is the main purpose of villi in the small intestine?

To churn foodTo increase surface area for absorptionTo produce acidTo store waste

What happens to food in the stomach?

It is absorbed into the bloodIt is broken down by acid and enzymesIt is eliminated as wasteIt is turned into bile

What is peristalsis?

A type of enzymeA muscular action that moves food through the digestive tractA nutrient found in foodA part of the small intestine

Based on the passage, why is digestion important for cellular respiration?

Digestion provides nutrients that cells use to produce energyDigestion helps the lungs get oxygenDigestion controls body temperatureDigestion removes waste from the blood

If the villi in the small intestine were damaged, what might happen?

More bile would be producedNutrient absorption would decreaseDigestion would speed upThe stomach would get larger

True or False: The large intestine is mainly responsible for absorbing most nutrients from food.

TrueFalse

True or False: Enzymes in saliva start the chemical breakdown of food in the mouth.

TrueFalse