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Comparing the traits of fish, reptiles, and amphibians and how they live in different environments.
If you found a mysterious animal near a pond, would you know if it was a fish, a reptile, or an amphibian just by touching it? The secret is all in their skin and how they breathe!
Fish are perfectly built for life in the water. Most fish are covered in scales, which are small, hard plates that overlap like shingles on a roof to protect their bodies. On top of these scales, fish have a thin layer of slime. This slippery coating helps them glide through the water with less friction and protects them from germs. Unlike us, fish don't have lungs to breathe air. Instead, they use gills. Gills are special organs that take oxygen out of the water as it passes over them. Because they have gills and scales, fish can spend of their lives underwater!
Let's look at a common pet goldfish: 1. Observe the body: It is covered in tiny, wet scales. 2. Watch the sides of the head: You will see flaps opening and closing. These are the gills working to pull oxygen from the water. 3. Feel (metaphorically): If you touched one, it would feel slippery because of its slime coat.
Quick Check
What are the two main features fish use to stay protected and move easily in water?
Answer
Fish use hard scales for protection and a slippery slime coat to move easily.
Reptiles, like snakes, lizards, and turtles, have a very different type of skin. Their skin is dry and scaly. Unlike fish scales, reptile scales are thick and tough to keep moisture inside their bodies. This allows them to live in very dry places, like deserts, without drying out. Another big difference is how they breathe. Even sea turtles that live in the ocean must come to the surface because all reptiles have lungs. They breathe air just like humans do! They do not have a slime coat, so they feel dry and bumpy to the touch.
Imagine an iguana sitting on a hot rock: 1. The sun is , but the iguana doesn't dry out because its dry scales lock in water. 2. It holds its breath while it moves, then stops to take a gulp of air using its lungs. 3. Unlike a fish, it has no slime, so sand doesn't stick to its body.
Quick Check
Why do reptiles have thick, dry skin instead of slimy skin?
Answer
To trap moisture inside their bodies so they don't dry out on land.
The word amphibian means 'double life.' These animals, like frogs and salamanders, start their lives in the water and usually move to land as adults. Amphibians have moist, smooth skin. They don't have scales! Their skin is so thin that they can actually breathe and drink water through it. When they are babies (like tadpoles), they use gills to breathe underwater. As they grow up, they go through a change called metamorphosis. Most adult amphibians grow lungs to breathe air, but they must stay near water to keep their skin damp and healthy.
Trace the life of a frog: 1. Stage 1: Starts as an egg in a pond. It hatches into a tadpole with gills. 2. Stage 2: It grows legs and its gills disappear as it develops lungs. 3. Stage 3: The adult frog lives on land but must jump back into the water frequently to keep its moist skin from drying out.
Which animal group has dry, scaly skin and breathes with lungs?
What is the process called when an amphibian changes from a water-breathing baby to a land-breathing adult?
Fish have a slime coat to help them stay dry.
Review Tomorrow
In 24 hours, try to remember: Which of the three groups (fish, reptiles, amphibians) has smooth, moist skin and no scales?
Practice Activity
Draw a picture of a pond and place one fish, one reptile, and one amphibian in the scene. Label their skin type and how they are breathing!