Plant Form and Function

Root Systems are the parts of a plant that grow under the ground. Roots are very important because they help a plant live and grow.

Have you ever pulled a weed or looked at a carrot? The part under the soil is the root system. Some roots are big and thick. Some are thin and spread out like a net. Even though roots can look different, they all do important jobs for the plant.

In this lesson, you will learn about two kinds of root systems: taproots and fibrous roots. You will also learn what roots do.

What do roots do?

• Anchor the plant. This means roots hold the plant in the soil so it does not fall over easily.
• Absorb water. Roots take in water from the soil.
• Take in nutrients. Nutrients are tiny bits in the soil that help plants grow.
• Store food. Some roots save food for the plant to use later.

You can think of roots like a plant's underground helper. They hold, drink, gather, and store.

Two main kinds of root systems

1. Taproot

A taproot has one main root that grows straight down into the soil. Smaller roots grow out from the sides of the main root.

Taproots are often thick and strong. They can go deep into the ground. This helps the plant reach water far below the surface.

Some taproots also store food. That is why some roots are big and thick.

Examples of taproots:

• Carrot
• Radish
• Beet
• Dandelion

If you look at a carrot, you are really looking at a taproot that stores food.

2. Fibrous roots

A fibrous root system has many thin roots that spread out in different directions. There is no one big main root.

Fibrous roots stay closer to the top of the soil. They spread out like a mat or a web.

These roots are very good at grabbing water from the top layer of soil. They also help hold the soil in place.

Examples of fibrous roots:

• Grass
• Wheat
• Rice
• Corn

If you pull up a small patch of grass, you may see lots of skinny roots all tangled together. That is a fibrous root system.

How are taproots and fibrous roots different?

• A taproot has one main root with smaller side roots.
• A fibrous root system has many thin roots and no one main root.
• Taproots often grow deeper into the ground.
• Fibrous roots often spread wide and shallow near the top of the soil.
• Some taproots store food very well.

Why do plants need roots?

Without roots, a plant would have a hard time standing up. Wind or rain might knock it over. Roots keep the plant steady in the ground.

Without roots, the plant would also have trouble getting water and nutrients. The roots pull these in from the soil so the rest of the plant can use them.

Some plants use their roots like a storage place. They keep extra food in the roots. Later, the plant can use that stored food to keep growing.

Worked Example 1: Finding the taproot

A plant has one big root going down and a few smaller roots coming out of it. What kind of root system is it?

Step 1: Look for the main root.

There is one big root.

Step 2: Match it to what you know.

One big main root means it is a taproot.

Answer: The plant has a taproot.

Worked Example 2: Finding the fibrous roots

A plant has lots of thin roots spreading out under the soil. There is no one big root. What kind of root system is it?

Step 1: Look at the roots.

There are many thin roots.

Step 2: Check for a main root.

There is no one big main root.

Answer: The plant has fibrous roots.

Worked Example 3: What job is the root doing?

A carrot plant has a thick root under the ground. The root holds extra food for the plant. What job is the root doing?

Step 1: Think about root jobs.

• Hold the plant in place
• Take in water and nutrients
• Store food

Step 2: Match the clue.

The clue says the root holds extra food.

Answer: The root is storing food.

Worked Example 4: Comparing two plants

Plant A is a carrot. Plant B is grass. Which plant most likely has a taproot, and which has fibrous roots?

Step 1: Remember the examples.

Carrot is an example of a taproot. Grass is an example of fibrous roots.

Answer:

• Plant A (carrot) has a taproot.
• Plant B (grass) has fibrous roots.

Let’s remember the big idea

Root systems help plants survive. They hold the plant in place, take in water, take in nutrients, and sometimes store food.

There are two main root systems to know:

• Taproot: one big main root, often deep, sometimes stores food
• Fibrous roots: many thin roots, spread out near the top of the soil

When you see a carrot, think taproot. When you see grass, think fibrous roots.

Summary

Roots are the underground parts of plants. They help plants stay in the soil, get water and nutrients, and sometimes store food.

Taproots have one main root, and fibrous roots have many thin roots. Both kinds of roots help plants grow strong and healthy.

Seed Development and Dispersal

Plants make new plants by making seeds. A seed is a tiny plant baby with food stored inside. When a seed gets what it needs, it can grow into a new plant.

But how does a seed get made? And how does it travel to a new place? In this lesson, we will learn how seeds grow inside fruits and how they are moved by wind, water, and animals.

1. How a seed begins

Many plants make flowers. Flowers help plants make seeds. Inside a flower are tiny parts that help start a new seed.

After the flower is helped by pollen, a tiny part inside the flower called an ovule begins to change. The ovule grows and becomes a seed.

At the same time, another part of the flower grows bigger and becomes the fruit. The fruit holds and protects the seeds.

So we can remember it like this:

• Ovule becomes a seed.
• Flower part around it becomes a fruit.

2. What is inside a seed?

A seed is small, but it has important parts inside.

• A baby plant
• Stored food for the baby plant
• A seed coat on the outside to protect it

The seed coat is like a little jacket. It helps keep the inside safe until the seed is ready to grow.

3. Why fruits are important

Fruits do more than taste good. Their job is to protect seeds and often to help seeds travel.

Some fruits are soft and juicy, like apples, peaches, and berries. Some are dry, like pods and nuts. No matter what they are like, fruits help keep seeds safe.

4. What is dispersal?

Dispersal means seeds are spread out and moved away from the parent plant.

This is important because if all seeds fell in one tiny spot, the new plants would fight for the same sunlight, water, and space.

When seeds spread out, they have a better chance to grow into healthy plants.

5. Seed dispersal by wind

Some seeds are very light. Some have fluff, wings, or tiny shapes that help them float in the air. The wind can carry these seeds away.

Dandelion seeds are a good example. Their fluffy tops act like little parachutes. Maple seeds are another example. They spin as they fall and can be blown away.

• Wind-dispersed seeds are often small and light.
• They may have wings or fluffy parts.

6. Seed dispersal by water

Some seeds and fruits can float. Water carries them to a new place.

A coconut is a famous example. It can float on water and travel far away. Seeds near rivers, ponds, or oceans may be moved this way.

• Water-dispersed seeds often have a way to float.
• They can travel across streams, rivers, or ocean water.

7. Seed dispersal by animals

Animals help move seeds in different ways.

Sometimes an animal eats a fruit. The seeds inside may be dropped later in a new place. This helps the seeds spread out.

Other seeds have hooks or sticky parts that cling to fur or feathers. The animal walks to another place, and the seeds fall off there.

Squirrels also help. They carry and bury nuts. Sometimes they forget where they put them. Then the nut may grow into a new plant.

• Animals may eat fruits and move the seeds.
• Seeds may stick to fur.
• Animals may carry and bury seeds.

8. Why different seeds travel in different ways

Plants live in many different places. A plant near water may have seeds that float. A plant in a windy field may have light seeds. A plant with tasty fruit may depend on animals.

These are called adaptations. An adaptation is a feature that helps a living thing do its job well. For seeds, the job is to stay safe and get to a good place to grow.

Worked Example 1: Finding the seed and fruit

A peach grows on a tree. Inside the peach is a hard pit with a seed inside it.

1. The part that became the seed was the ovule inside the flower.
2. The part that became the fruit was the flower part around it.

Answer: The seed formed inside the flower, and the peach fruit grew around it to protect it.

Worked Example 2: Which seed uses wind?

Look at these two seeds:

• Seed A is tiny and fluffy.
• Seed B is heavy and round.

Which seed is more likely to travel by wind?

Step 1: Think about what wind can carry best. Wind carries things that are light.

Step 2: Look for a helpful shape. Fluffy parts can help a seed float.

Answer: Seed A is more likely to travel by wind because it is tiny and fluffy.

Worked Example 3: Which seed uses water?

A seed has a thick outside and can float on a pond without sinking. How might it be dispersed?

Step 1: Notice the clue: it can float.

Step 2: Floating helps a seed move on water.

Answer: It is likely dispersed by water.

Worked Example 4: How do animals help?

A dog walks through grass. Later, burrs are stuck to its fur. The burrs fall off in another place.

How were the seeds dispersed?

Step 1: The seeds stuck to an animal.

Step 2: The animal moved to a new place.

Answer: The seeds were dispersed by animals.

Let’s compare the three main ways seeds spread

• Wind: light seeds, fluffy seeds, winged seeds
• Water: floating seeds or fruits
• Animals: seeds eaten, carried, buried, or stuck to fur

Important ideas to remember

• Seeds begin as ovules inside flowers.
• After they begin to grow, the ovules become seeds.
• The flower part around them grows into a fruit.
• Fruits protect seeds.
• Seeds are dispersed by wind, water, and animals.
• Dispersal helps plants grow in new places.

Brief Summary

Plants make seeds inside flowers. The ovule becomes a seed, and the flower part around it becomes a fruit. Fruits protect seeds and can help them travel. Seeds are spread by wind, water, and animals so new plants can grow in new places.

Germination Conditions means the things a seed needs to start growing. When a seed begins to sprout, it is called germination.

Seeds may look small and quiet, but they are alive. Inside a seed is a tiny baby plant. It waits until the conditions are right to begin growing.

Just like people need food, water, and a safe place to grow, seeds need certain things too. If a seed does not get what it needs, it may stay asleep and not sprout yet.

Let’s learn the main conditions that help many seeds germinate.

1. Water

Water is one of the most important things a seed needs. When a seed gets water, it softens. The seed coat, which is the outside covering, begins to open.

Then the tiny plant inside can start to grow. The first little root usually comes out first. This root helps the plant take in more water from the soil.

If there is too little water, the seed may stay dry and not sprout. If there is too much water, the seed may not grow well either.

2. Warmth

Many seeds need warmth to germinate. Warmth helps the seed wake up and begin growing.

If it is too cold, the seed may wait. That is why many plants sprout in spring, when the weather becomes warmer.

Different seeds like different temperatures, but many seeds need a place that is not too cold and not too hot.

3. Air

Seeds also need air. Even though seeds are in soil, tiny spaces in the soil hold air.

The seed uses air while it starts growing. If the soil is packed too tightly or filled with too much water, the seed may not get enough air.

4. Light or Darkness

Some seeds need light to germinate. Some seeds need darkness. Many seeds can germinate underground in the dark.

This means not all seeds are the same. A seed’s kind helps decide what it needs.

For 2nd grade, it is important to remember this: some seeds need light, and some do not.

5. Special Triggers

A few seeds need special things to start growing. Some seeds may sprout after a fire has passed through an area. Some may need very bright light. These are called special triggers.

This does not happen for every seed. It only happens for some kinds of plants. Nature has many different ways to help plants grow in the right place and time.

What happens when a seed germinates?

1. The seed gets water.
2. The seed begins to swell and soften.
3. The seed coat opens.
4. A tiny root comes out first.
5. A shoot begins to grow upward.
6. The young plant keeps growing.

This is the beginning of a new plant’s life.

What a seed needs and does not need at first

• Needs: water, air, and the right temperature
• Sometimes needs: light, darkness, or another special trigger
• Does not need right away: a lot of space or big leaves

The baby plant has stored food inside the seed to help it get started.

Worked Example 1

Mia puts one bean seed in dry soil by a sunny window. She never waters it.

Question: Will the seed probably germinate?

Answer: No, it probably will not germinate.

Why? The seed has sunlight, but it does not have water. Water is one of the main things a seed needs to start sprouting.

Worked Example 2

Leo plants two seeds. He gives both seeds water and air. One seed is kept in a warm room. The other is kept in a very cold place.

Question: Which seed is more likely to germinate first?

Answer: The seed in the warm room is more likely to germinate first.

Why? Many seeds need warmth to wake up and begin growing. The cold seed may stay asleep longer.

Worked Example 3

Sara gives a seed water every day, but the pot has no holes on the bottom, and the soil stays very soggy.

Question: What problem might the seed have?

Answer: The seed may not get enough air.

Why? Seeds need air in the soil. If there is too much water, the air spaces can fill up with water, and the seed may not grow well.

Worked Example 4

Two different kinds of seeds are planted. Both get water, air, and warmth. One kind sprouts in the light. The other kind sprouts only when covered by soil in the dark.

Question: What does this show?

Answer: It shows that different seeds can need different conditions.

Why? Some seeds need light to germinate, and some do not. Seeds are not all exactly the same.

Let’s compare

• A dry seed usually does not sprout.
• A watered seed may sprout.
• A warm seed often sprouts faster than a cold seed.
• A seed with air in the soil can grow better.
• Some seeds need light, but some need darkness.

Easy way to remember

Many seeds need water + air + warmth to begin growing.

We can think of it like this:

Seed + water + air + warmth = sprout

In math symbols, we can write:

\(1\) seed + water + air + warmth \(\rightarrow\) sprout

This is not regular math to solve. It is just a simple way to show what helps a seed start growing.

Summary

Germination is when a seed begins to sprout and grow. Most seeds need water, air, and the right temperature to germinate. Some seeds also need light, darkness, or another special trigger. When the conditions are right, the tiny plant inside the seed wakes up and begins to grow.

Plant Tropisms are ways plants grow in response to things around them. A plant cannot walk to a better spot, so it changes the way it grows. This helps the plant get what it needs to live.

Plants need sunlight, water, air, and space. A plant may bend, stretch, or curl as it grows. These growth changes are called tropisms.

Think of a plant like a quiet helper in nature. It does not talk or move from place to place, but it is always responding to the world. If light is on one side, the plant may grow toward it. If roots are in the soil, they grow downward. If a vine touches a fence, it may wrap around it.

There are three main plant tropisms to learn:

• Light tropism: a plant grows toward light.
• Gravity tropism: roots grow down, and stems grow up.
• Touch tropism: a plant changes how it grows when it touches something.

Let’s learn about each one.

1. Light Tropism

Plants use light to make their food. Because light is so important, many stems and leaves grow toward the light. This is called light tropism.

If a plant sits near a sunny window, you may notice it leaning toward the window. The plant is not trying to be silly. It is growing in the direction where it can get more light.

Example: A bean plant is on a table. The window is on the left side. After a few days, the stem bends left. The plant is showing light tropism.

2. Gravity Tropism

Gravity pulls things down toward the ground. Plants respond to gravity as they grow. This is called gravity tropism.

Roots usually grow downward into the soil. Growing down helps roots find water and hold the plant in place.

Stems usually grow upward. Growing up helps the plant reach light and air.

So, one plant has different parts doing different jobs:

• Roots grow down.
• Stems grow up.

Example: You plant a seed in a cup of soil. Soon, the root grows down and the shoot grows up. This is gravity tropism.

3. Touch Tropism

Some plants respond when they touch something. This is called touch tropism.

Vines are a great example. A vine may touch a stick, string, or fence. Then it begins to wrap around it as it grows. This helps support the plant.

Example: A pea plant vine touches a garden pole. After some time, the vine curls around the pole. The vine is showing touch tropism.

Why are tropisms important?

Tropisms help plants survive. They help plants get the things they need.

• Light tropism helps plants get sunlight.
• Gravity tropism helps roots get water and keeps the plant steady.
• Touch tropism helps some plants get support.

Without these growth responses, plants would have a harder time living and growing well.

Plant Parts and Tropisms

Different plant parts can respond in different ways.

• Roots: usually respond to gravity by growing down.
• Stems: usually respond to gravity by growing up and to light by growing toward it.
• Vines: often respond to touch by curling around objects.

This means one plant can show more than one tropism at the same time.

Worked Example 1

A flower pot is placed near a bright window. After one week, the stem leans toward the window.

Question: What tropism is this?

Answer: This is light tropism.

Why? The stem is growing toward the light from the window.

Worked Example 2

A seed starts to grow in the soil. The root goes down into the dirt. The stem grows up above the soil.

Question: What tropism is this?

Answer: This is gravity tropism.

Why? The root responds by growing down, and the stem responds by growing up.

Worked Example 3

A vine plant is growing next to a fence. When the vine touches the fence, it wraps around it.

Question: What tropism is this?

Answer: This is touch tropism.

Why? The plant changed its growth after touching the fence.

Worked Example 4

A small plant near a window has roots growing down into the soil and a stem bending toward the window.

Question: How many tropisms do you see?

Answer: You see two tropisms.

We can show it like this:

$$1\text{ gravity tropism} + 1\text{ light tropism} = 2\text{ tropisms}$$

Why? The roots growing down show gravity tropism. The stem bending toward the window shows light tropism.

How to remember the three tropisms

• Light = grow toward sunshine.
• Gravity = roots down, stems up.
• Touch = curl or wrap after touching something.

Try thinking about these questions:

1. If you turn a plant so the window is on the other side, which way might the stem grow?
2. If a root grows downward, what tropism is it showing?
3. If a vine wraps around a stick, what tropism is it showing?

Answers:

1. The stem may grow toward the new side with light.
2. Gravity tropism.
3. Touch tropism.

Brief Summary

Plants respond to the world by changing how they grow. These growth responses are called tropisms. Plants may grow toward light, roots may grow with gravity, and vines may respond to touch. Tropisms help plants get light, water, and support so they can live and grow.

Seasonal Adaptations are ways plants change or stay safe during different times of the year. Plants do not walk to a new place when weather changes. Instead, they use special parts and behaviors to help them live through winter, dry times, and shorter days.

Some plants lose their leaves. Some keep their leaves all year. Some slow down and rest. These changes help plants save water, save energy, and stay alive until better growing weather returns.

In this lesson, you will learn about deciduous plants, evergreen plants, dormancy, drought, and how plants respond to changing daylight.

What is a seasonal adaptation?

A seasonal adaptation is a helpful change that lets a plant survive during a certain season. Seasons bring changes in temperature, rain, snow, and sunlight. Plants must be ready for these changes.

For example, winter can be very cold. Water may freeze, and there is less sunlight each day. In summer, some places may get very dry. Plants need ways to handle both cold and dry conditions.

Deciduous plants

Deciduous plants are plants that lose their leaves during part of the year, usually in fall before winter. Many trees, such as maple and oak, are deciduous.

Leaves are important because they help a plant make food from sunlight. But leaves also lose water. In winter, when the ground may be frozen and water is hard to get, keeping many leaves can be a problem.

So, deciduous plants drop their leaves to save water and save energy. This helps the plant survive until spring.

Before leaves fall, they may change color. Then the plant lets the leaves go. During winter, the branches may look bare, but the plant is still alive.

Evergreen plants

Evergreen plants keep their leaves all year long. Many evergreens have leaves shaped like needles, such as pine and fir trees.

Needle-like leaves are helpful because they lose less water than big, flat leaves. Many evergreens also have a waxy coating on their needles. This coating helps keep water inside the plant.

Evergreens do not keep each leaf forever. They lose old needles a little at a time, not all at once. That is why they stay green through the seasons.

Dormancy

Dormancy is a resting time for a plant. During dormancy, the plant slows down. It does not grow much. It saves its energy for a better time, like spring.

Winter dormancy helps many plants survive cold weather. A tree may look like it is not doing anything, but inside, it is protected and waiting.

Some plants also become dormant during very dry times. If there is not enough water, resting can help the plant stay alive until rain comes.

Drought

A drought is a long time with very little rain. During a drought, plants may not get enough water.

Plants have different ways to handle drought. Some plants have deep roots to reach water far underground. Some have thick stems or leaves that store water. Some plants stop growing for a while. Some drop leaves to lose less water.

These are all adaptations that help plants survive dry weather.

Changing daylight hours

Plants also respond to how much sunlight they get each day. In fall and winter, days become shorter. In spring and summer, days become longer.

Shorter days can signal a plant that winter is coming. This can help the plant get ready by slowing growth, dropping leaves, or becoming dormant.

Longer days can signal that spring is coming. Then plants may begin to grow new leaves, make flowers, and grow faster again.

Plants do not think like people do, but they do respond to changes in the world around them. Daylight helps tell them what season it is.

How plant parts help with seasonal adaptation

• Leaves: May be dropped to save water, or may be needle-shaped to hold water better.
• Roots: Can grow deep to find water during dry times.
• Stems and trunks: Help support the plant and move water and food. Some can store water.
• Buds: Tiny new leaves or flowers may stay protected inside buds during winter.

Why these adaptations matter

If plants could not adapt to seasons, many would not survive. Cold, ice, dry weather, and less sunlight can make life hard for plants.

Seasonal adaptations help plants live through tough times. Then, when the weather becomes warmer or wetter, plants can grow again.

Worked Example 1: Deciduous or evergreen?

Question: A tree loses all of its leaves in fall and has bare branches in winter. Is it deciduous or evergreen?

Step 1: Think about what deciduous means. Deciduous plants lose their leaves during part of the year.

Step 2: Compare the tree to that meaning. This tree loses all its leaves in fall.

Answer: The tree is deciduous.

Worked Example 2: Why do leaves fall?

Question: Why might a deciduous tree drop its leaves before winter?

Step 1: Remember that winter can be cold and water may be harder for plants to get.

Step 2: Leaves lose water. Keeping many leaves in winter can make it harder for the plant.

Answer: The tree drops its leaves to save water and energy.

Worked Example 3: What helps an evergreen?

Question: A pine tree stays green in winter. What leaf trait helps it survive?

Step 1: Think about evergreen leaves. They are often thin like needles.

Step 2: Needle-like leaves and a waxy covering help keep water in.

Answer: Its needle-like, waxy leaves help it survive.

Worked Example 4: Daylight and dormancy

Question: In fall, the days get shorter. How might a plant respond?

Step 1: Shorter days can tell a plant that winter is coming.

Step 2: The plant may slow down, drop leaves, or go dormant.

Answer: The plant may become dormant or get ready for winter.

Let’s compare deciduous and evergreen plants

• Deciduous plants: Lose leaves during part of the year.
• Evergreen plants: Keep leaves all year.
• Deciduous plants: Often have broad, flat leaves.
• Evergreen plants: Often have needle-like leaves.
• Both: Have adaptations that help them survive changing seasons.

Signs of seasonal adaptation you can observe

• Leaves changing color and falling in autumn
• Evergreen trees staying green in winter
• Trees with bare branches in winter
• New buds and leaves growing in spring
• Plants looking dry or resting during hot, dry weather

Think about it

If two plants live in the same place, they may still adapt in different ways. One may drop leaves. Another may keep waxy needles. Both ways can help plants survive.

This shows that plants are living things with many smart survival features. Their roots, stems, leaves, and buds all help them through the seasons.

Brief Summary

Seasonal adaptations help plants survive winter, drought, and changing daylight. Deciduous plants drop their leaves to save water and energy. Evergreen plants keep special leaves, often needles with a waxy covering, to help them hold water. Many plants also go into dormancy, a resting time, until conditions are better for growing again.