How Do Animal Parts Help Them Live?

But look at a chicken. A chicken has feet too. Yet a chicken does not swim. If a chicken stepped in deep water, it would have trouble!

Why can a duck swim so well, but a chicken cannot? Let's look closely at their feet!

• How are the duck's feet different from the chicken's feet?
• Why do you think the duck's feet help it swim?

All animals have external parts. That means parts on the outside of their body. Eyes, legs, wings, and tails are all external parts.

Each part has a job. The shape of a part helps it do its job. Let's learn two big ideas!

Scientists watch animals closely. They look at how body parts work. Let's do an investigation to see how webbed feet help ducks swim!

What you need: A bowl of water, your hand, and a plastic fork.

• Fill a big bowl with water.
• Spread your fingers apart. Push your hand through the water. Feel how easy it is to push.
• Now hold your fingers tight together so your hand is flat. Push through the water again. What do you feel?
• Try using a plastic fork in the water. Then try a flat spatula or spoon. Which one pushes more water?

When your fingers are together, your hand works like a duck's webbed foot. It pushes more water! That is how ducks swim so fast.

When we tried the investigation, we found something cool! A flat hand pushes more water than spread-out fingers. The water goes right between your fingers when they are apart!

This is just like a duck's webbed feet. The skin between a duck's toes makes each foot wide and flat. When the duck pushes its foot back in the water, it pushes a LOT of water. That is what makes the duck move forward!

A duck's webbed feet help it do three important things:

Here is something really cool. The shape of a body part always tells us about its job. This is true for ALL animals! Scientists call this structure and function. That means the shape of something helps it do its job.

Let's look at more examples!

See the pattern? The shape of a body part matches the job it does! Sharp claws are for grabbing. Long legs are for jumping. A hard shell is for protecting. Webbed feet are for swimming.

People look at animal body parts to get ideas! When people wanted to swim faster, they looked at duck feet. They made swim fins that look just like webbed feet!

When you wear swim fins on your feet, your feet become big and flat like a duck's feet. You can push more water and swim faster. Isn't that cool? People copied the duck!

This is what scientists and engineers do. They look at how animals solve problems. Then they use those ideas to help people!

• External part — A body part on the outside of an animal, like legs, eyes, or wings.
• Webbed feet — Feet that have skin between the toes, making them wide and flat like a paddle.
• Structure — The shape of a body part. What it looks like.
• Function — The job a body part does. What it is for.
• Needs — Things an animal must have to live, like food, water, and safety.