Biological Structures and Functions

Fruit Development and Seed Protection

Plants make new plants by making seeds. A seed is like a tiny baby plant with food packed inside.

But seeds need help while they grow. They need something around them to protect them. That is where fruit comes in.

When a flower is pollinated, the part of the flower called the ovary begins to grow bigger. It swells and turns into a fruit. Inside the fruit, the seeds grow and stay safe.

So, fruit is not just a tasty snack. A fruit has an important job: it covers, protects, and helps move seeds.

How a fruit begins

Many plants start with a flower. Flowers help plants make seeds.

After pollination, the flower changes. The ovary starts to grow. As it gets bigger, it becomes a fruit.

The seeds develop inside. The fruit forms around them like a cover.

• Flower comes first.
• Pollination happens.
• The ovary swells.
• A fruit forms.
• Seeds grow inside.

What fruit does

Fruit has two big jobs.

1. Protect the seeds
2. Help the seeds travel

1. Fruit protects the seeds

Seeds are small and need protection while they grow. The fruit wraps around the seeds and helps keep them safe.

Some fruits are soft and juicy. Some are hard and dry. Both kinds help protect the seeds inside.

• An apple protects its seeds in the center.
• A peach has a soft outside and a hard pit around the seed.
• A pea pod holds the seeds in a long case.
• A pumpkin protects many seeds inside its thick fruit.

2. Fruit helps seeds travel

Plants cannot walk from place to place. So their seeds need help moving away from the parent plant.

Fruit can help seeds travel in different ways.

• Animals eat fruit and carry seeds away.
• Animals drop fruit or carry it to new places.
• Dry fruits may split open and let seeds fall out.
• Some fruits are light and can be moved by wind or water.

When seeds move to a new place, they may get room, water, and sunlight to grow into new plants.

Examples of fruits and seeds

An apple is a fruit. The little brown seeds inside are the seeds it protects.

A tomato is also a fruit. It has seeds inside, too.

An orange is a fruit with seeds inside its sections.

A bean pod is a fruit. The beans inside are seeds.

This can feel surprising because we often think of fruit only as sweet foods. In science, a fruit is the part that forms from the flower ovary and holds the seeds.

Worked Example 1

A flower is pollinated. Later, the ovary gets bigger and seeds are growing inside. What is the ovary turning into?

Answer: It is turning into a fruit.

Why: After pollination, the ovary swells and becomes the fruit. The seeds grow inside it.

Worked Example 2

A child cuts open an apple and sees small brown seeds in the middle. What job is the apple doing for the seeds?

Answer: The apple is protecting the seeds.

Why: The fruit covers the seeds and keeps them inside while they develop.

Worked Example 3

A bird eats a berry and flies to another place. Later, the seeds from the berry end up far away from the plant. How did the fruit help?

Answer: The fruit helped the seeds travel to a new place.

Why: Animals can eat fruit or carry it, which helps move seeds away from the parent plant.

Worked Example 4

Look at these plant parts:

• flower
• fruit
• seed

Which order shows what happens first, next, and last?

Answer: flower → fruit → seed inside the fruit

Why: The flower comes first. After pollination, the ovary becomes fruit. Then the seeds grow inside the fruit.

Let’s remember

• A seed can grow into a new plant.
• A flower helps the plant make seeds.
• After pollination, the flower’s ovary swells.
• The ovary becomes a fruit.
• The fruit protects the seeds.
• The fruit can also help seeds spread to new places.

Brief Summary

Fruits grow from flowers after pollination. The ovary swells and becomes the fruit.

The fruit protects the seeds while they grow. It can also help the seeds move to new places, where new plants may grow.

Vertebrate vs. Invertebrate Classification

Animals come in many shapes and sizes. Some animals are big, and some are small. Some fly, some swim, and some crawl.

Scientists sort animals into groups. One important way to sort animals is by asking: Does the animal have a backbone?

A backbone is a row of small bones down the middle of the back. It helps hold the body up and protect the body.

If an animal has a backbone, it is called a vertebrate.

If an animal does not have a backbone, it is called an invertebrate.

Let’s learn about both groups.

1. Vertebrates

Vertebrates are animals with a backbone. You can often think of the backbone as part of the animal’s inside support.

Many animals you know are vertebrates. People are vertebrates too.

• Dog
• Cat
• Fish
• Bird
• Frog
• Snake
• Human

These animals may look very different, but they all have one thing in common: they have a backbone.

2. Invertebrates

Invertebrates are animals without a backbone.

Some invertebrates have soft bodies. Some have hard shells on the outside. But they do not have a backbone inside their bodies.

• Ant
• Butterfly
• Spider
• Worm
• Snail
• Octopus
• Jellyfish

These animals are all invertebrates because they do not have a backbone.

How to Tell the Difference

When you want to classify an animal, ask this question:

Does it have a backbone?

• If yes → vertebrate
• If no → invertebrate

You can think of it like this:

Backbone = vertebrate

No backbone = invertebrate

Why This Helps

Sorting animals into groups helps us learn about them. It helps us notice how animals are alike and how they are different.

For example, a bird and a fish do not look the same. But both are vertebrates because both have backbones.

A worm and a butterfly do not look the same either. But both are invertebrates because neither has a backbone.

Worked Example 1: Dog

Let’s classify a dog.

1. Ask: Does a dog have a backbone?
2. Yes, a dog does have a backbone.
3. So, a dog is a vertebrate.

Answer: Dog → vertebrate

Worked Example 2: Worm

Now let’s classify a worm.

1. Ask: Does a worm have a backbone?
2. No, a worm does not have a backbone.
3. So, a worm is an invertebrate.

Answer: Worm → invertebrate

Worked Example 3: Fish

Let’s try a fish.

1. Ask: Does a fish have a backbone?
2. Yes, a fish has a backbone.
3. So, a fish is a vertebrate.

Answer: Fish → vertebrate

Worked Example 4: Snail

This one can be tricky because a snail has a shell.

1. Ask: Does a snail have a backbone?
2. No, a shell is not a backbone.
3. So, a snail is an invertebrate.

Answer: Snail → invertebrate

Remember These Important Ideas

• A backbone is inside the back.
• Animals with a backbone are vertebrates.
• Animals without a backbone are invertebrates.
• A shell is not the same thing as a backbone.

Let’s Practice Thinking

Classify these animals by asking if they have a backbone:

• Cat → vertebrate
• Butterfly → invertebrate
• Frog → vertebrate
• Spider → invertebrate

Quick Summary

Animals can be sorted into two big groups: vertebrates and invertebrates.

Vertebrates have a backbone. Invertebrates do not have a backbone.

To classify an animal, ask one simple question: Does it have a backbone? If yes, it is a vertebrate. If no, it is an invertebrate.

Insects are tiny animals with special body parts. We can learn a lot by looking closely at how an insect is built.

Insects have body parts that help them live, move, find food, and stay safe. One very important insect body part is its exoskeleton. An exoskeleton is a hard outer covering on the outside of the body.

Let’s learn the main parts of an insect and what each part does.

What makes an insect an insect?

An insect has 3 main body parts:

• Head
• Thorax
• Abdomen

An insect also has 6 legs. We can count them as:

$$2 + 2 + 2 = 6$$

The legs are attached to the thorax, which is the middle body part.

The head

The head is the front part of the insect. The head helps the insect sense the world around it.

• It has eyes to help the insect see.
• Many insects have compound eyes. That means their eyes are made of many tiny parts that work together.
• The head also has a mouth for eating.
• Many insects have antennae on the head. Antennae help insects feel and smell.

The thorax

The thorax is the middle part of the insect’s body. This part helps the insect move.

• All 6 legs are attached to the thorax.
• Some insects also have wings attached to the thorax.

If you want to know where the legs are, look at the thorax.

The abdomen

The abdomen is the back part of the insect’s body.

The abdomen holds important parts inside the insect’s body. It helps the insect live and grow.

The exoskeleton

An insect does not have skin like we do on the outside. Instead, it has a hard outer covering called an exoskeleton.

Exo means outside. So an exoskeleton is a skeleton on the outside.

The exoskeleton helps an insect in many ways:

• It protects the insect’s body.
• It gives the insect shape.
• It helps support the insect when it moves.

You can think of an exoskeleton like a little suit of armor on the outside.

Why is the exoskeleton important?

Because insects are small, they need strong protection. Their exoskeleton helps keep them safe from bumps and from being hurt easily.

The exoskeleton also helps the insect keep its body together and gives it a firm outside.

How to remember insect body parts

1. Head = seeing, smelling, eating
2. Thorax = moving with 6 legs
3. Abdomen = back body part

Examples of insects

Many animals are insects if they have the right body parts.

• An ant is an insect.
• A bee is an insect.
• A butterfly is an insect.
• A beetle is an insect.

These insects may look different, but they all share the same basic body plan: head, thorax, abdomen, and 6 legs.

Worked Example 1: Counting insect legs

A bug has 6 legs. Is it built like an insect?

Let’s check:

• Insects have 6 legs.
• This bug has 6 legs.

So, yes, it could be an insect.

Worked Example 2: Finding the body part

A bee uses its eyes and antennae to notice flowers. What body part is it using most?

Eyes and antennae are on the head.

So the answer is head.

Worked Example 3: Where are the legs attached?

A student points to the middle part of an ant and says, “This is where the legs are attached.” Is the student correct?

Yes. The middle part is the thorax, and insect legs are attached there.

So the student is correct.

Worked Example 4: What protects the insect?

A beetle bumps into a leaf. What hard outside part helps protect its body?

The hard outside covering is the exoskeleton.

So the answer is exoskeleton.

Let’s compare the parts

• Head: eyes, antennae, mouth
• Thorax: 6 legs, helps movement
• Abdomen: back body part
• Exoskeleton: hard outside covering that protects the insect

Quick check

Ask yourself these questions:

• Does an insect have 3 body parts?
• Does an insect have 6 legs?
• Are the legs attached to the thorax?
• Does the insect have a hard outside covering called an exoskeleton?

If you can say yes, you are thinking like a scientist!

Summary

Insects are animals with a special body plan. They have a head, thorax, and abdomen.

They also have 6 legs, and the legs are attached to the thorax. Many insects have compound eyes and antennae on the head.

An insect’s hard outer covering is called an exoskeleton. The exoskeleton protects the insect and helps give its body shape.