WHAT IS A PLANT?
Plants are one of the five main
groups of living things. These groups are called kingdoms. The plant kingdom
includes such living things as grasses, trees, ferns, bushes, and flowers.
Botanists, the scientists who study plants, have counted more than 260,000
species (kinds) of plants.
Plants vary greatly in size and
shape. Some plants are so small they can hardly be seen. Other plants tower
above the land. The giant sequoia trees of California are one of the largest
living things on Earth. They can grow to heights of nearly 300 feet (90
meters)!
Just like animals, plants are made
up of tiny structures called cells. But unlike animal cells, plant cells are
surrounded by a stiff material called cellulose. Most animals move around and
eat other things. Plants are different. Plants that grow on land usually stay in
one place and make their own food.
Most plants are green because they
have a green chemical called chlorophyll. Plants are different from mushrooms
and other fungi. Fungi do not have chlorophyll.
WHAT ARE THE MAIN KINDS OF PLANTS?
Almost all the members of the
plant kingdom are seed plants. They grow from seeds. Most seed plants are
flowering plants, or angiosperms.
But there are some groups of
plants that do not grow from seeds. Botanists call these groups bryophytes,
ferns, lycophytes, and horsetails.
WHAT ARE FLOWERING PLANTS?
People who plant flower gardens
fill them with flowering plants. Oaks, maples, and other trees that turn bright
colors in autumn are flowering plants. The grasses on lawns are flowering
plants. Almost all the fruits and vegetables you eat come from flowering
plants.
Flowering plants make seeds that
are inside a covering. Angiosperm, the name for flowering plants, means
“enclosed seed.”
You probably have seen many seeds
of angiosperms. The seeds are inside fruit. Bite into an apple, a peach, or a
pear and you will find one or more seeds. The seeds started to grow inside the
beautiful blossoms that covered these fruit trees in the spring.
WHAT ARE OTHER SEED PLANTS?
Unlike flowering plants, some seed
plants make seeds that are not inside a covering. They are called gymnosperms, a
word that means “naked seed.”
The best-known kinds of gymnosperms
are conifers. Conifers are evergreens. They stay green all year long.
Arborvitae, cedar, cypress, fir, hemlock, juniper, pine, and spruce trees are
all conifers.
Conifers and other gymnosperms do
not have flowers. Conifers do have leaves, but they are usually thin like
needles. The seeds of conifers are in cones.
WHAT ARE THE MAIN PARTS OF PLANTS?
Most plants have three main parts:
roots, stems, and leaves. The roots are in the ground. They hold the plant in
the soil. Roots take up water and minerals the plant needs.
Stems usually are above ground.
They carry food and water. The stems of some plants, such as dandelions, are
thin and delicate. Trees have thick, strong stems. The stems are trunks covered
with bark.
Leaves come out of the stems of
plants. Green plants use light, water, minerals, and carbon dioxide (a gas in
the air) to make food in their leaves.
Leaves have many different shapes.
Some are sharp spines that protect the plant from animals. Some leaves are
brightly colored. Flowers are a kind of leaf.
HOW DO PLANTS GROW?
Most plants grow from seeds.
Seeds need soil, water, and light to grow. A bean is a seed. You can make a bean
plant grow. Here’s how.
Put a bean in a paper cup filled
with soil. Set the cup near a window where there is plenty of sunlight. Water
the bean often. A root will grow downward from the bean. A green shoot will
start to grow upward from the bean. Soon you will see leaves start to grow out
of the shoot, or stem.
Wind and water may carry some
seeds far from the plants that made them. Sometimes seeds are “planted” by
animals that eat fruit. Apples, peaches, and cherries are examples of
seed-bearing fruits that animals like to eat.
Cherries, for instance, are a
favorite food of birds. After a bird has eaten the fruit, it may fly off and
drop the cherry stone, or seed, far away. This seed may start to grow and make a
new cherry tree.
WHERE DO SEEDS COME FROM?
Many kinds of plants have male
and female parts. These plants reproduce, or make seeds, sexually. In flowering
plants, the male and female parts are in the flowers. In pine trees and other
conifers, the male and female parts are in the cones. Conifers have male and
female cones.
The male part of a flower is
called the stamen. It gives off a powdery substance called pollen. The female
part is called the pistil. An egg forms in the pistil. Pollination occurs when
some of the pollen gets to the pistil. A pollen grain joins with an egg. When
this happens, a seed begins to grow.
In some species, the pollen and
egg can come from the same plant. In other species, they must come from
different plants. But how does pollen move? Insects, wind, and water can all
help move the pollen.
Have you seen bees or
butterflies around flowers? Bees and butterflies like to drink nectar from the
flowers. As they enjoy their tasty treat, some of the pollen sticks to their
bodies. They carry it with them to other flowers, leading to pollination.
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