Grade by Grade
B. Life Systems · Growth and Changes in Plants

Plant Parts at Work: Roots, Stems and Leaves

B2.2 A1.1 A1.5About 35 minutes
Learning goals
  • I can identify the root, stem and leaf of different plants.
  • I can describe how roots, stems and leaves help a plant survive.
  • I can compare roots, stems and leaves of different plants.
  • I can find and share facts about plant parts.

Words to know

root
The part of a plant that holds it in the ground and soaks up water and nutrients.
stem
The part that holds the plant up and carries water and food between the roots and leaves. A tree trunk is a stem.
leaf
The part that uses sunlight to make food for the plant.
taproot
One big, thick main root that grows straight down, like a carrot.
fibrous roots
Many thin roots that spread out like a messy mop, like grass roots.
bark
The tough outer layer of a woody stem, like a tree trunk. It protects the tree.

Remember from Grade 1

In Grade 1 you learned that plants have parts, like roots, stems, leaves and flowers. Now you are a Grade 3 scientist! Let's look closely at how each part does its job to help the plant survive in its environment.

Think about a dandelion

Have you ever tried to pull a dandelion out of the lawn? It is hard! Often the top breaks off and the root stays in the ground. A few weeks later, the dandelion grows back.

Why? Its long, strong root holds on tight and stores food. Every part of a plant has a job like this.

A whole dandelion pulled from the soil, showing its long thick root, jagged leaves and yellow flower on a stem.
Look at how long and thick the dandelion's root is. It anchors the plant and stores food, which is why dandelions are so hard to pull out. AI-generated image
groundflowerleafstemroots
The main parts of a flowering plant: flower, leaf, stem and roots. The dashed line shows the top of the ground.

Roots: the anchors and drinking straws

Roots grow under the ground. They:

  • hold the plant in place so wind and rain cannot knock it over,
  • soak up water and nutrients from the soil,
  • in some plants, store food for later (a carrot is a root full of stored food).

There are two main kinds of roots.

taproot (carrot)fibrous roots (grass)
Left: a taproot, one thick main root with tiny side roots. Right: fibrous roots, many thin roots spreading out.

A taproot goes deep to find water far down. Carrots, dandelions and beets have taproots.

Fibrous roots spread out near the top of the soil. They catch rain quickly and hold soil together so it does not wash away. Grass and corn have fibrous roots.

Stems: the holders and highways

The stem grows up from the roots. It:

  • holds the plant up so the leaves can reach the light,
  • carries water up from the roots to the leaves through tiny tubes,
  • carries food made in the leaves to other parts of the plant.

Some stems are soft and green, like a bean plant's stem. Some are hard and woody, like a tree trunk. A tree trunk is a giant stem covered with bark, which protects it from insects, heat and cold.

Leaves: the food makers

Leaves catch sunlight. They use light, air and water to make food for the whole plant. Leaves also have tiny openings that let air in and out.

Leaves come in many shapes:

  • Broad, flat leaves (like a maple leaf) catch lots of sunlight.
  • Needles (like on a pine tree) are thin and waxy. They lose less water, so they can stay on the tree all winter.
  • Thick, fleshy leaves (like an aloe plant) store water.
PartMain jobsExamples
rootholds plant in the ground; takes in water and nutrients; can store foodcarrot (taproot), grass (fibrous roots)
stemholds plant up; carries water and foodbean stem (soft), maple tree trunk (woody)
leafmakes food using sunlight; lets air in and outmaple leaf (broad), pine needles
Roots, stems and leaves and how they help a plant survive.
Worked example

Let's look closely at a plant

Look at a dandelion (or picture one). Identify its root, stem and leaves, and tell how each one helps it survive in a lawn.

  1. Root: a long taproot. It goes deep for water, so the dandelion survives dry weather. It stores food, so the plant can grow back after being cut.
  2. Stem: the flower stalk is hollow and bendy. It holds the flower up high where insects can see it.
  3. Leaves: long leaves with jagged edges that lie flat in a circle close to the ground. They catch sunlight, and a lawn mower often passes right over them.

Each part helps the dandelion survive in a lawn: a deep root for water and regrowing, a tall stem to hold up the flower, and low leaves that make food and escape the mower.

Worked example

Let's watch water travel up a stem

What happens if we put a stalk of celery in coloured water?

  1. Put a fresh celery stalk (with its leaves) in a glass with water and a few drops of food colouring.
  2. Wait a day.
  3. Look at the leaves: they have spots of the colour.
  4. A grown-up cuts the stalk across. You can see small coloured dots: these are the ends of the tiny tubes.

Water travels up the stalk through tiny tubes, all the way to the leaves. That is how a stem carries water.

Just for fun

Ever had a celery string stuck in your teeth? Those strings are bundles of the stem's tiny water tubes. You were flossing with a plant's drinking straws!

Hands-on activity

Be a plant detective

You need: 3 different plants you are allowed to look at (a house plant, a weed from the yard and a vegetable like a carrot with its top, or green onions), a magnifying glass if you have one, paper and pencil crayons.

  1. For each plant, draw it and label the root, stem and leaves.
  2. Look closely. Is the root a taproot or fibrous? Is the stem soft or woody? Are the leaves broad, needles or thick?
  3. Use a book or a website a grown-up helps you choose to find one fact about one of your plants.
  4. Make a small poster called "How each part helps my plant survive" and explain it to someone in your family.

Grown-up note: Help choose plants that are safe to touch (no poison ivy, which has leaves in groups of three, and no wild parsnip or giant hogweed, whose sap can burn skin in sunlight). Any cutting of celery or roots is done by a grown-up. Wash hands afterward.

Your turn

1

Name two jobs of the roots.

2

What is a tree trunk?

3

What is the main job of leaves?

4

What kind of root does a carrot have?

5

How does water get from the roots to the leaves?

6

Why are pine needles good for staying on a tree in winter?

7

What does bark do for a tree?

More practice: warm-up

1

Which part grows under the ground: roots or leaves?

2

Which part holds the plant up?

3

Which part catches sunlight?

4

What kind of roots does grass have?

5

Name a plant with needles.

More practice: on your own

1

Why is it hard to pull out a dandelion?

2

A big storm blows hard. Which part keeps a tree from falling over? Explain.

3

Why do farmers sometimes plant grass on a hill to stop soil from washing away?

4

Is the stem of a sunflower more like a bean's stem or a tree trunk? Explain.

5

A plant's stem was snapped in half. Why will the leaves at the top soon wilt?

Challenge

1

An aloe plant has thick, fleshy leaves. What kind of environment do you think it comes from? Why?

2

When you eat a carrot, which plant part are you eating, and why is it full of food?

3

Compare the roots of a maple tree and a grass plant. Give one way they are the same and one way they are different.

Check your understanding

Quiz

1.

Which part of a plant holds it in the ground?

2.

Which part makes food for the plant using sunlight?

3.

What does a stem do?

4.

A carrot is an example of a...

5.

Celery in coloured water gets coloured leaves. This shows that...

6.

Why do pine needles help a pine tree survive winter?

For parents and teachers

Big idea (B2.2, part 1): Each plant part helps the plant survive: roots anchor and absorb water and nutrients (and sometimes store food), stems support and transport, and leaves make food. The plant detective activity practises research (A1.1) and communicating with labelled diagrams and correct vocabulary (A1.5). Flowers, seeds, fruits and cones come in the next lesson.

Accuracy note: The celery "stalk" is botanically a leaf stalk (petiole), not a true stem, but it has the same water-carrying tubes and is the classic way to show water moving up. A white carnation in coloured water works too.

Common difficulties:

  • Thinking a tree trunk is not a stem. Point out that it holds the tree up and carries water, just like a small plant's stem.
  • Thinking all roots look like a carrot. Pull up a clump of grass or a weed together to see fibrous roots.

How to help: On a walk, ask, "Is that stem soft or woody? Are those leaves broad or needles?" At dinner, name the plant part you are eating. Avoid poison ivy ("leaves of three, let it be") and supervise any cutting.