The Respiratory System for Middle School Science

You breathe in and out every moment without even thinking about it. But have you ever wondered what’s really happening when you take a breath? Your body depends on a constant supply of oxygen to keep its cells alive and working, and that job belongs to your respiratory system.

The respiratory system is a group of organs and tissues that work together to help you breathe. It takes in the oxygen your cells need and removes the carbon dioxide they no longer want.

In this reading passage, you'll explore how air travels through your body, how your lungs exchange gases, and how the respiratory system works closely with the circulatory system to deliver oxygen where it’s needed most. You’ll also learn how exercise, pollution, and diseases can affect your breathing—and how to keep your lungs healthy.

You can check out the pages of my body system unit from Teachers Pay Teachers below. You can also continue on to read more about the respiratory system.

The Respiratory System

Every second, your body needs oxygen to work properly. That’s where the respiratory system comes in. It’s the system that helps you breathe, bringing oxygen into your body and getting rid of carbon dioxide, a waste gas your body doesn’t need.

Even though breathing feels automatic, it’s actually a complex process involving your nose, windpipe, lungs, and even muscles like your diaphragm. These parts work together to move air in and out and to make sure oxygen gets into your blood.

Functions of the Respiratory System

The respiratory system is essential for life. Its main job is to bring oxygen into your body and remove carbon dioxide. But it does even more than that. Here are the key functions of the respiratory system:

1. Breathing

Breathing is the process of moving air in and out of your lungs. When you inhale (breathe in), your lungs fill with oxygen-rich air. When you exhale (breathe out), your lungs release carbon dioxide. Muscles like the diaphragm and the rib muscles power this movement of air.

2. Gas Exchange

Inside your lungs are tiny air sacs called alveoli, where oxygen passes into the blood and carbon dioxide passes out. This exchange of gases happens in the capillaries that surround each alveolus. Oxygen is then carried by the blood to your cells, and carbon dioxide is brought back to the lungs to be exhaled.

3. Oxygen Delivery

The oxygen you breathe in doesn’t just stay in your lungs—it travels through the bloodstream. The respiratory system works closely with the circulatory system to deliver oxygen to every part of your body so your cells can make energy.

4. Removal of Waste Gases

Your body creates carbon dioxide as a waste product when it uses oxygen. The respiratory system gets rid of this carbon dioxide by moving it from the blood to the lungs and then out of the body when you exhale.

5. Protection and Filtration

Your respiratory system also helps protect you from harmful particles. Your nose hairs, mucus, and tiny hairs called cilia trap dust, germs, and other particles so they don’t reach your lungs.

6. Speaking and Making Sounds

Your respiratory system helps you talk! Air from your lungs passes through the larynx (voice box), making the vocal cords vibrate. This creates sound when you speak, sing, or laugh.

The respiratory system does more than help you breathe—it helps your cells make energy, removes waste, protects your lungs, and even helps you communicate!

Parts of the Respiratory System

The respiratory system is made up of organs and structures that work together to help you breathe. Each part has a special job in moving air into your body, exchanging gases, and protecting your lungs. Let’s take a look at the major parts:

Nose and Nasal Cavity

Air usually enters your body through the nose. Inside the nose, hairs and mucus trap dust, pollen, and germs. The air is also warmed and moistened, so it’s easier on your lungs.

Mouth

The mouth is another way air can enter and leave your body, especially when you’re breathing heavily during exercise.

Pharynx (Throat)

The pharynx is a passageway for both air and food. Air from the nose and mouth passes through the pharynx on its way to the lungs.

Larynx (Voice Box)

The larynx is located below the pharynx. It contains the vocal cords, which vibrate to create sound when you speak. It also helps ensure air goes into the lungs and food goes into the stomach.

Trachea (Windpipe)

The trachea is a tube that carries air from the larynx to the lungs. It is lined with tiny hairs called cilia and mucus to trap dust and germs.

Bronchi and Bronchioles

The trachea splits into two tubes called bronchi—one for each lung. These tubes branch into smaller tubes called bronchioles inside the lungs, like branches of a tree.

Alveoli

Millions of tiny air sacs called alveoli are at the ends of the bronchioles. This is where gas exchange happens—oxygen goes into the blood, and carbon dioxide comes out.

Lungs

The lungs are the main organs of the respiratory system. They contain the bronchi, bronchioles, and alveoli. They expand and contract as you breathe.

Diaphragm

The diaphragm is a dome-shaped muscle below the lungs. When it contracts, it creates space for the lungs to expand and fill with air. When it relaxes, it pushes air out of the lungs.

Together, these parts help you breathe, talk, and stay healthy by delivering oxygen and removing carbon dioxide. They work like a well-organized team to keep your body running smoothly!

Gas Exchange Within the Capillaries

Your body needs a steady supply of oxygen to make energy, and it must get rid of carbon dioxide, which is a waste gas. This gas exchange happens in the lungs and at the cells in your body. The process that makes this exchange possible is called diffusion.

What Is Diffusion?

Diffusion is the movement of particles—like gases—from an area where they are crowded (high concentration) to an area where they are less crowded (low concentration). It doesn’t require any energy; it happens naturally. In your body, oxygen and carbon dioxide move by diffusion during gas exchange.

Diffusion in the Lungs

When you breathe in, air fills tiny air sacs in your lungs called alveoli. These sacs are surrounded by capillaries, which are small blood vessels. The air in the alveoli has a lot of oxygen because you just inhaled, while the blood coming into the lungs has very little oxygen. Because of this difference in concentration, oxygen diffuses from the alveoli into the capillaries and enters the bloodstream. At the same time, carbon dioxide, which is more concentrated in the blood, diffuses from the blood into the alveoli so it can be exhaled.

Diffusion at the Cells

After picking up oxygen from the lungs, the blood carries it to cells all over the body. In the capillaries near the cells, the blood has more oxygen than the cells do, so oxygen diffuses from the blood into the cells. The cells use this oxygen to make energy. As they work, the cells produce carbon dioxide, which builds up inside them. Now, the carbon dioxide is at a higher concentration in the cells than in the blood, so it diffuses into the capillaries to be carried away and eventually removed by the lungs.

What Is Cellular Respiration?

Every cell in your body needs energy to do its job—whether it's helping you move, think, grow, or heal. But where does that energy come from? It comes from a process called cellular respiration, which happens inside your cells.

Cellular respiration is the process by which cells use oxygen and nutrients (like glucose from food) to make energy. This energy is stored in a molecule called ATP (adenosine triphosphate), which cells use to power all their activities.

Here’s a simple version of the formula:

Glucose (from food) + Oxygen → Energy (ATP) + Carbon Dioxide + Water

That means the food you eat and the oxygen you breathe in are turned into usable energy, and the leftovers—carbon dioxide and water—are waste products. The carbon dioxide is carried away by the blood and sent to the lungs to be exhaled.

Without cellular respiration, your cells wouldn’t get the energy they need to survive. It’s like charging your phone’s battery—but for your body! This is why breathing and eating healthy food are both essential—oxygen and nutrients are the fuel for life.

Air-Breathing Animals and Water-Breathing Animals

Animals need oxygen to survive, but different species have evolved different ways to get it based on where they live. Air-breathing animals, such as humans, birds, and most mammals, use lungs to take in oxygen from the air. When they inhale, air travels through their nose or mouth, down the trachea, and into the lungs, where tiny air sacs called alveoli allow oxygen to pass into the bloodstream while removing carbon dioxide. Breathing air is generally more efficient than breathing water because air contains a higher oxygen concentration.

In contrast, many aquatic animals, like fish, breathe using gills. Gills are thin, feathery structures that absorb oxygen directly from the water. As water flows over the gills, oxygen diffuses into the blood while carbon dioxide is released into the water. Since water holds much less oxygen than air, fish must constantly move water across their gills—either by swimming or by pumping water through their mouths. Some amphibians, such as frogs, can even breathe through their skin while underwater, adding another respiration method.

Despite their differences, both systems perform the same basic function: exchanging gases to keep the animal alive. Both lungs and gills provide moist surfaces for oxygen to enter the blood and carbon dioxide to exit. They also both rely on the circulatory system to transport gases throughout the body. While air-breathing animals tend to breathe more efficiently, water-breathing animals have specialized structures to survive in low-oxygen environments.

The respiratory systems of air- and water-breathing animals differ in structure and environment, but they share the common goal of delivering oxygen to the body and removing waste gases to support life.

How the Respiratory System Interacts with Other Body Systems

The respiratory system doesn’t work alone—it teams up with other systems in the body to keep you healthy and alive. Its main job is to bring in oxygen and remove carbon dioxide, but to do this effectively, it must work closely with other systems.

Circulatory System: The respiratory and circulatory systems work together to move oxygen and carbon dioxide throughout the body. After you breathe in oxygen, it enters the lungs and passes into the blood through tiny air sacs called alveoli. The circulatory system, made up of the heart and blood vessels, then transports that oxygen-rich blood to every cell. At the same time, the blood carries carbon dioxide (a waste gas made by cells) back to the lungs, where you breathe it out. Without the heart pumping blood, the oxygen wouldn’t reach the body’s cells.

Muscular System: You need your muscular system to breathe! The diaphragm, a dome-shaped muscle at the bottom of your chest, moves down when you inhale to pull air into your lungs. It moves up when you exhale to push air out. Other muscles, like those between your ribs, also help expand and shrink your chest to move air in and out.

Nervous System: The nervous system controls your breathing automatically. A part of your brain called the brainstem tells your body when to breathe, even when you're sleeping. It monitors how much carbon dioxide is in your blood and adjusts your breathing rate to keep everything balanced.

Digestive System: The digestive system provides the nutrients that the body’s cells need to make energy. The respiratory system supplies the oxygen needed for that process. Together, oxygen and nutrients are used by cells to release energy through a process called cellular respiration. Without oxygen from the respiratory system, the digestive system’s nutrients couldn’t be turned into usable energy.

In short, the respiratory system works closely with other systems—especially the circulatory, muscular, nervous, and digestive systems—to ensure your body gets the oxygen it needs and can release waste gases. This teamwork helps keep every part of your body functioning properly.

Flashcards on the Respiratory System

Flashcards are the best way to practice remembering new information. You can get digital and printable flashcards at Teachers Pay Teachers, or you can use the flashcards here for free!

The Human Body

Middle School Science