Science High School Reviewer | Grade 4 Science | Life Science | Kingdoms of Life | Lesson 6: Parts of a Plant

A plant has different parts. Each part plays
a role in helping the plant survive in its environment.

6.1 The role of roots

Roots take up water and nutrients
from the ground. They also keep
plants firmly in the soil. Some roots
even store food.
Roots are covered with root hairs.
These are thin cells that look like
thread. Root hairs take in the water
and nutrients that plants need.
All roots do the same jobs, but
different plants have different kinds
of roots. Carrots and dandelions
have one large root called a taproot.
Grasses have fibrous (FY•bruhs) roots
that spread out into the soil.

The role of roots

If you have ever tried to pull up a large weed, you
know one of the main jobs that roots do—they anchor
the plant firmly in the ground. Because most roots are
underground, they can absorb, or take in, water and
mineral nutrients from the soil around them. One thing
that roots do not do is make food. Root cells do not
contain chlorophyll. However, some roots store food.
The plant uses this food when it cannot produce enough
during photosynthesis.

Fibrous roots

Roots grow away from the stem in search of water and
nutrients. In some plants, the roots spread out in many
directions, forming a fibrous root system. They are able
to absorb water and mineral nutrients from a large area.
The plant can take in the water before it runs off.
The plant stores the extra water in its stem. The
roots in a fibrous system are all about
the same size. They grow longer, but
they don’t grow very thick or very
deep. Most grasses and trees have
fibrous roots. Plants that grow in
hot, dry areas also have fibrous roots.

Carrots, turnips, and dandelions
have a taproot system. This system has
a large main root called a taproot.
It grows straight down. The taproot
absorbs water and nutrients from
the soil. As it stores food for the
plant, it grows thicker. Some smaller
roots grow from the side of the taproot.
Root hairs extend from the sides of
the main taproot and the smaller roots.
Each of the tiny root hairs also absorbs
water and nutrients from the soil. They help
the plant get the materials it needs to grow
and to make food.

Plants Without
Roots
Some plants do not have
true underground roots.
Yet they are able to get
what they need to make
their own food. These
air plants, as they are
called, absorb moisture
directly from the air.
They take the nutrients
they need from dust in
the air. Spanish moss is
an air plant that grows
in many parts of the
southern United States.
You can see clumps of it
hanging from the tree in
the photo.

6.2 The Roles of Leaves and Stems

You know that most plants are made of cells—millions of
them. Similar cells are grouped to do certain jobs. For example,
some cells make food, and some store it. Some cells provide
support for the plant, and some help carry nutrients throughout
the plant. Groups of similar cells form tissues, such as wood and
the outer covering of plants. Different tissues work together
to form organs, such as leaves, stems, and roots.
Most plants have all these parts, whether the
plant is a redwood tree or a dandelion.

Leaves
All leaves have the same
role. Their job is to produce
food so the plant can
survive in its environment.
To make that job easier,
leaves are different
shapes and sizes. For
example, the leaves
of plants, such as pine
trees, are thin, sharp needles.
The narrow shape prevents the
tree from losing too much water.
Other plants, such as the banana plant,
grow in places with plenty of water.
Their leaves can be almost as wide
as a kitchen table.

Stems
What does a tree trunk have in common
with the thin stalk of a grass plant? They
both are stems. Stems vary greatly in size
and shape, but they all have the same two
basic functions. They carry water, minerals,
and food between the roots and the leaves.
The stems also support the plant, holding the
leaves up so they can get sunlight.
Some stems are soft and flexible. You can
bend them in your hand. Examples include
the stems of daisies, dandelions, and tomato
plants. These stems are usually green and
carry out photosynthesis just like leaves do.
Some stems grow strong and thick. They
can support larger plants such as trees. The
tree’s outer layer of dead cells forms bark that
protects the plant.

The Role of Stems
A plant’s stem grows above the
ground. The stem moves food, water,
and nutrients throughout the plant.
Stems also hold the plant upright so
it does not fall over.
There are two kinds of stems. Most
trees and shrubs have woody stems.
Woody stems protect the plant and
give it extra support. Smaller plants
have stems that are soft, green, and
bendable. They rely on the pressure
of watery sap for support.
tap root
Nonwoody
stems are soft
and bendable.

Why are leaves important?

Like all living things, plants need energy. Animals
eat food to get energy. Plants make their own food.
Most plants use leaves to collect light from the Sun.
Photosynthesis
Plants use the energy in sunlight to make food
from water and carbon dioxide. This is the process
of photosynthesis (foh•toh•SIN•thuh•sis). Most
photosynthesis takes place in the leaves of plants.
Photosynthesis begins when sunlight hits the leaf.
The light energy goes into the plant cells. From there
it enters the chloroplasts. Inside the chloroplasts,
chlorophyll collects the light energy.
When the chloroplasts gather enough energy,
a change takes place. Water and carbon dioxide
combine to form plant sugars, or food. The cells let
oxygen out as a waste product.

Parts of a leaf

Collecting Carbon Dioxide
Where do leaves get carbon
dioxide gas for photosynthesis?
Carbon dioxide enters through
tiny holes on the bottom of leaves.
The holes are called stomata
(stoh•MAH•tuh). A single one is a
stoma (STOH•muh).
Collecting Water
The roots of a plant take up
water from soil. Small tubes called
veins (VAYNZ) carry the water from
the roots to the stem. Veins also
move the water into each leaf.
Leaves have a thin covering to
keep water in. This layer is called
the epidermis. It protects leaves the
way skin protects your body.
Transpiration
If a plant has too much water,
its stomata stay open. The extra
water escapes. This process is called
transpiration. If a plant has too
little water, it closes its stomata.
The water stays inside the leaf.
Respiration
Like all living things, plants
need energy. They get it from the
sugars made during photosynthesis.
The sugars provide plants with food.
Veins carry the sugars from
the leaves to the rest of the plant.
Inside the cell, mitochondria break
down the sugars. The energy stored
inside the sugars is released. This
process is called respiration. During
respiration, cells take in oxygen and
give off carbon dioxide.
Photosynthesis takes place only in
the light. Respiration happens both
day and night. It takes place in all
living cells, not just plant cells.

epidermis
vein
Parts of a Leaf stoma

What are mosses and ferns?

What are mosses
and ferns?
In the cool forests of North
America, the ground is a moist,
green carpet. When you walk on
this carpet, it feels spongy. If you
look closely, you will see small
structures in the carpet. They are
mosses. Look around the forest
and you will find the delicate
leaves of ferns.
Spores
Both ferns and mosses are
seedless plants. Instead of using
seeds to make new plants, they
make spores. A spore is a cell in a
seedless plant that can grow into a
new plant.

How Spores Grow
Spores grow inside tough spore
cases. The cases protect the spores
from too much heat or too little
water. When the spore cases open,
the spores are released. They drift
through the air and then settle.
Spores that land on damp ground
can grow into new moss or fern
plants. Like all plants, spores need
light, nutrients, and water to grow.
If their needs are met, the cycle of
life starts all over again.

How do we use plants?

Plants do much more than just
add beauty to our world. Plants give
us the food we eat and are useful in
many other ways.
Plants as Food
Lettuce and spinach are the leaves
of plants. If you eat carrots or beets,
you are eating roots. Celery and
asparagus are stems. Broccoli and
cauliflower are flowers. Rice and
beans are seeds. You may think all
fruits are sweet, but tomatoes and
cucumbers are fruits, too.
Medicines and More
People have used certain plants
as herbs or medicines for a long
time. Today, we are finding more
medicines that come from plants.
We use trees to build things like
furniture and toys. Plants can
be burned as fuel for heating
or cooking. Plants are used for
clothing, too. Woven shirts and
denim come from the cotton plant.