Digestion & Body Systems

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Digestion & Body Systems
Life Science
Grades 3-4 | 20 sessions

Students learn about structure and function, systems, and human body systems, with a focus on the digestive system. They also learn to visualize and use text features as they read, and to write scientific descriptions. They learn and use scientific vocabulary, such as interact, nutrients, evidence, and model.

Click Here to Download the Correlation of Digestion and Body Systems with the Common Core State Standards for English Language Arts Grade 3

Click Here to Download the Correlation of Digestion and Body Systems with the Common Core State Standards for English Language Arts Grade 4

» Download Unit Description


Do it:

Students engage in hands-on activities, such as investigating a model of how food moves through the intestines. Students also build their own system that sorts pom-pom balls by size.

Talk it:

Students are provided with many opportunities for small group discussions to help them make sense of science ideas. For example, students share what they’ve learned about a particular body system, and debate which system in the human body is the most important.

Read it:

Students read five science books, including Voyage of a Cracker about what happens to food as it passes through the parts of the digestive system. Students use comprehension strategies such as visualizing, and learn how to navigate informational text.

Write it:

Students write descriptions, including a descriptive paragraph about the stomach. Throughout the unit, students write to record observations and reflect on their learning.

Student Books

Learning Goals

Science Literacy
Science Knowledge
  • Systems
  • Digestive System
  • Body Systems
  • Structure and Function

Science Inquiry

  • Visualizing
  • Making Explanations from Evidence
  • Using Models
  • Comparing and Contrasting Explanations

Nature and Practices of Science

  • Understanding that Science Knowledge is Based on Evidence
  • Recognizing that the Scientific Community Seeks to Improve Explanations
  • Understanding How Scientists Engage in the Practices of Science
  • Visualizing
  • Using and Creating Diagrams
  • Using Nonfiction Text Features
  • Making Explanations from Evidence


  • Writing Descriptions
  • Using Scientific Language and Vocabulary


  • Participating in Scientific Discourse
  • Making Explanations from Evidence
  • Using Scientific Language and Vocabulary

Science Content

The Digestion and Body Systems unit introduces students to the idea of systems- an important way of thinking in science- and to human body systems through a focus on the digestive system.

Systems- A system can be defined as a group of parts that interact or function together as a unit. Systems are less a class of things than a way of thinking about combinations of interacting parts and how they work together. Students learn to think about the ways in which the parts of a system interact, the affects that a change to one part of a system can have on the system as a whole. They learn about systems that are made up of smaller subsystems.

Structure and function: An important concept related to systems is structure and function. The structure (shape and features) of a part is directly related to its function (what it does). This idea is helpful in analyzing systems, including living systems.

Human body systems: Students learn about the circulatory, respiratory, musculo-skeletal, renal, nervous, and digestive systems of the human body. There is a focus on the digestive system in order to allow more in-depth exploration of one body system. In addition, each student works with a group to investigate one of the other body systems as well. Students learn about the basic function and most important organs and parts of each body system. Students learn about the ways in which different body systems work together. They learn how doctors use evidence to diagnose problems in human body systems.

Digestive system: The digestive system brings in food, breaks it into smaller pieces, absorbs nutrients from the food, and eliminates wastes. The mouth tastes food and begins digestion by breaking food down with the teeth and with saliva. The esophagus is a mucus-lined tube that squeezes food down from the mouth to the stomach. In the stomach, acid juices continue to digest the food. As food is squeezed by muscles through the small intestine, nutrients from the food are absorbed into the blood stream. In the large intestine, excess water is absorbed. The waste that is left is excreted through the anus, a sphincter. There are many other sphincters (ring-shaped muscles that open and close) in other places in the digestive system as well.