---
title: "Gas Exchange & Breathing"
description: "Describe the structure of the human gas exchange system (trachea, bronchi, bronchioles, alveoli) and explain how the mechanism of breathing — using pressure changes from rib and diaphragm movement — m"
canonical: https://lightmysky.com/learn/science/gas-exchange-and-breathing-mt_V9SQS9gLFw
source: https://lightmysky.com/learn/science/gas-exchange-and-breathing-mt_V9SQS9gLFw.md
retrieved: 2026-10-19
---

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# Gas Exchange & Breathing

Describe the structure of the human gas exchange system (trachea, bronchi, bronchioles, alveoli) and explain how the mechanism of breathing — using pressure changes from rib and diaphragm movement — moves air in and out of the lungs

Subject: Science · Area: Organisms & Life Processes · Ages 12 to 13
Page: https://lightmysky.com/learn/science/gas-exchange-and-breathing-mt_V9SQS9gLFw

## Ready when they can

- Labels a diagram of the lungs showing trachea, bronchi, bronchioles, and alveoli
- Explains that breathing in lowers air pressure in the chest and air rushes in
- Describes how the structure of alveoli (large surface area, thin walls, good blood supply) aids gas exchange

## Lesson: How You Breathe: The Journey of Air

When you run for the bus you pull in extra air, and that air follows a clear path. It travels down your throat into the trachea, or windpipe. The trachea splits into two tubes called bronchi, one leading into each lung. Inside the lungs, the bronchi branch again and again into thinner tubes called bronchioles, like the branches of a tree getting smaller and smaller.

*(drawing: Air moves through smaller and smaller tubes until it reaches the alveoli at the very end.)*

**Example.** At the end of each bronchiole sit tiny air sacs called alveoli. They have very thin walls, a huge surface area, and are wrapped in tiny blood vessels. Just like with diffusion, a short distance and a large surface area make gas exchange fast: oxygen crosses into the blood and carbon dioxide crosses out.

Breathing in works by changing the pressure inside your chest. Your diaphragm, a sheet of muscle under your lungs, flattens and pulls down, and your rib muscles pull your ribcage up and out. This makes your chest bigger, so the pressure inside drops below the pressure outside, and air rushes in to even it out.

**Tip.** Breathing out reverses this. Your diaphragm relaxes and curves back upward, your ribs move down and in, your chest gets smaller, and the pressure inside rises above the pressure outside, pushing air back out.

**Recap.** Air flows through the trachea, bronchi, bronchioles, and alveoli, and breathing works by changing the pressure inside your chest so air rushes in or gets pushed out.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Cells to organ systems](https://lightmysky.com/learn/science/cells-to-organ-systems-mt_7hB8s5eOP1)
- [How Diffusion Works](https://lightmysky.com/learn/science/how-diffusion-works-mt_i80I-1MLP2)

## Opens up

- [CPR and the Recovery Position](https://lightmysky.com/learn/personal-and-social-development/cpr-and-the-recovery-position-mt_ahwfva-o1j)
- [Aerobic Respiration](https://lightmysky.com/learn/science/aerobic-respiration-mt_mquPi2IP-J)
- [Heart Structure & Double Circulation](https://lightmysky.com/learn/science/heart-structure-and-double-circulation-mt_TR2oTy9c2M)