Oxygen Coloring Sheet

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Learning about How Do Fish Breathe Underwater? was made possible by: Award-winning science curriculum by Apologia.

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How Do Fish Breathe Underwater?

Have you ever wished you could swim underwater for a long time? Many years ago, people invented scuba diving gear so they could explore beneath the water’s surface. But long before scuba suits, fish were already doing this with no challenge at all! How exactly did God design fish to breathe underwater? That’s what we’re diving into today. We’ll also look at some other amazing creatures with unique ways of breathing!

Why Is Breathing Important?

Before we talk about how fish, frogs, and spiders breathe, let’s first ask: Why is breathing important?

Have you ever stopped to think about your breathing? Probably not—you just do it! God designed our bodies to take around 16-30 breaths per minute without us even noticing. But why?

Because our bodies, and all living things, need oxygen to survive.

Oxygen is a chemical element that is essential for life. It gives us the energy we need for everything we do. We get oxygen by breathing air, but not all creatures breathe the same way. Some animals, especially those in the water, have incredible ways of getting oxygen.

How Do Fish Breathe Underwater?

Breathing underwater is tricky because, while creatures need oxygen, there isn’t much of it in the water. In fact, while air contains about 21% oxygen, water contains less than 1% dissolved oxygen! That means fish need an extremely effective way to get oxygen.

God designed fish with gills to help them do this.

Gills are special organs full of blood vessels that pull oxygen from the water. When a fish scoops up water in its mouth, that water flows over the gills. The oxygen from the water moves into the fish’s blood, which then carries oxygen throughout its body.

Fish also have a special system called the countercurrent exchange system that helps them get the most oxygen possible. This means that as water flows over the gills in one direction, the blood inside the gills flows in the opposite direction. This system allows fish to absorb more oxygen than if the blood and water flowed the same way. It’s an incredible design by our great engineering God!

How Do Frogs Breathe Through Their Skin?

Frogs spend a lot of time in the water, but they don’t have gills. Instead, frogs breathe in two ways:

• On land: Frogs breathe using lungs, just like we do.
• In water: Frogs can breathe through their skin!

This process is called cutaneous respiration. Because frogs have thin, moist skin, oxygen from the water diffuses straight through their skin and into their blood vessels.

Diffusion is a process where substances spread from areas of high concentration to low concentration. Think about dropping food coloring into a glass of water—it starts in one spot and then spreads. That’s diffusion!

Since there is more oxygen in the water than in the frog’s blood, the oxygen naturally spreads into the frog’s body. What an incredible design!

How Do Spiders Breathe Using Book Lungs?

Now let’s jump out of the water and look at an amazing way land creatures breathe. Did you know spiders don’t have lungs like we do? Instead, they have book lungs!

Book lungs are thin, plate-like structures inside a spider’s body that look like the pages of a book. Air flows between these plates, and oxygen moves into the spider’s hemolymph (which is similar to blood).

This unique breathing system is another example of God’s creative design in nature. Book lungs help spiders survive in different environments, even in tiny spaces where regular lungs wouldn’t fit!

What Is the Breath of Life?

God created so many different ways for His creatures to breathe—including us. Right now, take a deep breath in. Hold it for a second. Now let it out.

Breathing gives life to our bodies, just like it did when God created the first human.

Genesis 2:7 says, “Then the Lord God took dust from the ground and formed a man from it. He breathed the breath of life into the man’s nose, and the man became a living person.”

Imagine God carefully forming Adam’s body, then breathing His own breath into him. That breath gave Adam life!

Job 33:4 also says, “The Spirit of God created me, and the breath of the Almighty gave me life.”

Every breath we take is a gift from God. Even the amount of oxygen in our air is perfectly designed—if it were slightly higher, wildfires would be out of control; if it were lower, large creatures wouldn’t survive.

Psalm 150:6 says, “Let everything that breathes praise the Lord.”

So today, let’s thank God for the breath of life and for His incredible design in nature!