Materials & Prep
Prepare a board or projected chart with columns Before exercise, After exercise, and What it shows. Copy one heart-and-lungs organizer per student with arrows labeled lungs, blood, heart, muscles and sentence frames. Have a timer available. Choose a safe movement such as marching in place, with seated arm movements or another teacher-approved option available. Remind students to follow school procedures, use a comfortable pace, and stop or choose the alternate movement if they feel pain, dizziness, or unusual discomfort.
Opening observation
Ask“After a minute of marching or another comfortable movement, what do you predict will change: your breathing, your heartbeat, both, or neither? Why?” Students first show a prediction with fingers or a quick sketch, then do 45 seconds of teacher-led movement. Students may march, move arms while seated, or use another accessible movement.
Have students notice without needing new vocabulary: place a hand on the chest or wrist if comfortable, notice how quickly the chest rises, and compare these sensations with rest. Partners share one observation. All students can succeed by observing and comparing their own bodies; no pulse-counting accuracy is required yet.
Connect“You noticed that exercise makes your breathing and heartbeat change. Those changes are clues about what is happening inside. Today we will explain what the heart and lungs are doing to help working muscles.” Record two or three observations for use later.
Mini-lesson and model
DisplayDraw this sequence: air enters lungs → oxygen moves into blood → heart pumps blood to muscles. Add a return arrow: muscles send carbon dioxide-containing blood back toward the lungs → lungs remove carbon dioxide when we breathe out.
ExplainDuring exercise, muscles need more oxygen to release energy for movement and produce more carbon dioxide. The lungs move oxygen from the air into the blood and move carbon dioxide from the blood into the air we breathe out. The heart pumps the blood so these materials can travel between the lungs and muscles. The heart does not make oxygen, and the lungs do not push blood through the body.
ModelUse the opening observations as evidence. Say, “If the muscles are working harder, they need supplies more quickly and make waste more quickly. The lungs increase breathing to exchange more gases, and the heart beats faster and pumps more blood to the muscles.” Avoid presenting faster breathing as the lungs “making” oxygen. Emphasize that the heart and lungs work together, not separately.
Worked exampleDisplay this teacher-created observation: “At rest, a student counted 15 heartbeats in 15 seconds and 4 breaths in 30 seconds. After one minute of comfortable marching, the student counted 24 heartbeats in 15 seconds and 8 breaths in 30 seconds.” Think aloud: “The heartbeat count rose from 15 to 24, so the heart was pumping faster. The breaths rose from 4 to 8, so the lungs were moving air more often. My explanation must connect these changes to the muscles’ needs: more oxygen had to reach the muscles, and more carbon dioxide had to return to the lungs.” The common error is to say, “The heart needs more oxygen, so it pumps faster.” Correct it: “The working muscles are the main reason for the increased demand in this example.”
Guided practice
Students complete the first two rows of the organizer with the teacher: lungs to blood, then heart to muscles. They draw arrows and use the sentence frame, “During exercise, the lungs so that .” Invite responses such as “take in more air so more oxygen can enter the blood.”
Check for understandingShow three cards or write three choices: lungs, heart, or muscles. Read each statement and have students point to the correct choice, then explain the connection with a partner: “moves blood,” “brings oxygen into the blood,” and “needs more oxygen when it works harder.” For the final statement, “removes carbon dioxide from the blood,” students may point to lungs. Listen for students who confuse oxygen with carbon dioxide, and immediately trace each gas through the diagram.
Model one complete explanation aloud: “During exercise, the muscles work harder. The lungs bring more oxygen into the blood and remove more carbon dioxide. The heart pumps the blood faster so oxygen reaches the muscles and carbon dioxide can return to the lungs.”
Collaborative body-systems investigation
Have students work in pairs or groups of three with the organizer and the two observations from the worked example. Assign roles of reader, arrow-drawer, and explainer, with roles changeable for access. Students complete these steps:
- Circle what changed after exercise: heartbeat, breathing, or both.
- Draw an arrow from lungs to blood and label it oxygen.
- Draw an arrow from muscles back toward lungs and label it carbon dioxide.
- Add the heart to the route and write what it does.
- Write a four-sentence explanation using the frames: “Exercise makes the muscles . The lungs . The heart . This helps because .”
ScaffoldKeep the labeled diagram visible and provide a word bank: muscles, oxygen, carbon dioxide, blood, pump, breathe in, breathe out, faster. Students may explain by pointing to the diagram and saying one sentence at a time before writing. Pair students so one partner traces the arrows while the other reads the sentence frames.
CirculateAsk, “Where does oxygen enter the blood?” “Which organ pumps the blood?” and “What returns to the lungs?” Require students to point to evidence on the diagram before answering.
ExtensionStudents add a fifth sentence explaining why breathing and heartbeat usually return closer to resting levels after the movement stops, using the idea that the muscles no longer need as much oxygen as during exercise.
Closing explanation
Students complete an exit ticket: “Explain what the heart and lungs do during exercise. Include what happens to oxygen, what happens to carbon dioxide, and why breathing or heartbeat changes.” Students may write, draw and label arrows, or give the explanation orally to the teacher if that is an established classroom response option.
Check the response for three required ideas: the lungs move oxygen into the blood, the heart pumps blood to and from working muscles, and the lungs remove carbon dioxide as muscles work harder. Invite two students to share different parts of the explanation, then return to the opening prediction and ask students to revise it with one new reason.