# The Relay Race

![Figure 1: A teenage runner in track gear stands on a school field, hand on chest, breathing hard after a relay race, with a friendly coach beside her](https://goa-cc-uat-aili-app-001.azurewebsites.net/api/generate/6b01bf94-1e78-4d1a-845b-9bad42bcf1b3/asset/972)

Priya was gasping after the four hundred metre relay. "Why does my heart pound like that?" she asked, hand on her chest.

Coach Dinh grinned. "Your body's a team, just like your relay squad. Right now your muscle cells need more oxygen, so your heart pumps faster and your lungs grab more air."

"So my lungs are like the runner handing off the baton?" Priya asked.

"Exactly. Lungs pass oxygen to your blood, blood carries it to muscle cells, and those cells use it for energy. Skin cells cool you with sweat. Nerve cells send the signal to breathe harder."

"One team, different players," Priya said, catching her breath.

"That's a body system," Dinh said. "Everything balanced, working together."

## Words to know

- **cell**: the basic building block of living things
- **system**: parts working together for a shared job, like the circulatory system
- **stimulus**: a change, such as exercise, that the body responds to
- **tissue**: a group of similar cells working together, such as muscle tissue

Curriculum link: [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17320), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17320), [Outcome](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17321), [Topic](https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17317)

[Listen to the narration](https://goa-cc-uat-aili-app-001.azurewebsites.net/api/generate/6b01bf94-1e78-4d1a-845b-9bad42bcf1b3/asset/979)

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*AILI audio story · language en · model claude-sonnet-5 · generated 2026-09-17 · id 6b01bf94-1e78-4d1a-845b-9bad42bcf1b3*

### Sources

- node:n1: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17319)
- node:n2: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17320)
- node:n3: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17320)
- node:n4: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17321)
- node:n5: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17319)
- node:n6: Sciences › Science (7–9) › Grade 8 (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17317)
- node:n7: Sciences › Science (7–9) › Grade 8 › Unit B: Cells and Systems › Outcomes for Science, Technology and Society (STS) and Knowledge (https://goa-cc-uat-aili-app-001.azurewebsites.net/explore/node/17322)