Life-forms We Can’t Live Without
Plants are one of two major Kingdoms of
life forms. There are about 300,000 plant species on
Earth. Plants are the only life forms that can produce their own food using
energy from sunlight. Plants produce almost all of the oxygen in
the air that humans and other animals breathe. Plants are also an important
source of food, building materials, and other resources that make life possible
for Earth’s animals.
The plant kingdom consists of a wide range
of species. New plant species are being discovered every day. All fit into
Mosses & Liverworts: Mosses and liverworts are green
plants that are usually small. Their leaves are often just one cell thick.
Neither mosses nor liverworts have any woody tissue, so they never grow very
large. There are about 14,000 species.
Ferns: Ferns are a very ancient family
of plants. Early fern fossils show
that ferns are older than land animals and
far older than the dinosaurs. They were thriving on Earth for 200 million
years before flowering plants evolved.
Ferns live in sheltered areas under the forest canopy,
along creeks and streams, and in other wet places. They cannot grow well
in dry areas. There are about 12,000 species.
Cone Plants: Most cone plants, or conifers, are trees.
They represent some of the oldest and largest living species on Earth. Conifers
are often called evergreen trees,
because their leaves (thin needles) usually remain on the trees all year.
They have no flowers or fruits. Instead, seeds appear on cones and are scattered
by the wind or by animals. There are about 650 species.
Flowering Plants: Flowering plants include many of the
most familiar plants. The distinctive feature of this plant group is the
flower, a cluster of specialized leaves that help in reproduction.
Not all flowers are as bright and obvious as the sunflower blossoms in the
picture. Oaks, ivy, and grasses also produce flowers. Their flowers are not
as showy, so people don’t always notice them. All flowering plants
produce seeds from which new plants grow. There are about 270,000 species.
Shoots, Roots, and Other Important Plant Parts
The basic plant structure includes two organ systems:
the shoot system and the root system. The shoot system consists of the parts
of the plant that are above ground such as leaves, buds, and stems. In flowering
plants, flowers and fruits are also part of the shoot system. The root system
is made up of those parts of the plant below ground, such as the roots, tubers,
Click on the picture below to learn where these plant parts are found and
what they do.
Ready, Set, Grow!
Most plants grow from seeds, bulbs, or spores.
Since plants cannot move, they use animals, birds,
and the wind to scatter, or disperse, their seeds. Seeds come in all sizes.
Some flower seeds are as small as grains of salt. Others, such as coconuts,
are quite large.
After it germinates,
the first thing a growing seed does is send out a root. The root anchors the
plant and absorbs nutrients and
water from the soil. Next, a sprout with the first leaves grows. The leaves
reach toward the sunlight.
Food from the Sun
Plants are the only organisms that
have a green pigment called chlorophyll in
many of their cells. Chlorophyll is found mainly in the leaves. It allows plants
to make food (types of starch)
from sunlight, water, and a gas called carbon
dioxide. This special plant process is called photosynthesis.
Plants release the gas oxygen during photosynthesis.
Minerals from the Soil
Minerals from the soil help build the solid material in plant roots, stems,
and leaves. Carbon, hydrogen, and oxygen from the air and water make up over
90% of most plants.
Plants Make Life Possible
One of the most important things plants do
is create oxygen. This makes life on Earth possible for animals. Large areas
of plants such as forests and grasslands are needed for creating oxygen. Scientists
and conservationists worry that if large areas of uncut forest are not protected,
the whole planet’s survival system could be harmed.
Food for Life
A cluster of fruit ripens on this grapevine. Each grape contains seeds for
a new plant. Many animals, including people, love to eat the fruit of many
different plant species.
In addition to making food for themselves, plants make food for animals. Animals
eat many different plant parts. For example, cows, horses, and antelope eat
the leaves of grass. Primates, such as monkeys, eat fruits and leaves. People
eat almost all parts of a plant including underground roots and tubers (potatoes,
carrots, and radishes). We also eat leaves (lettuce, spinach), fruits (oranges,
apples, bananas), and seeds (rice, wheat, and corn). Even the bark can be good!
The cinnamon on a breakfast roll comes from the bark of a cinnamon tree. However,
not all plants are good to eat. Some plants are poisonous.
Plants are the largest and oldest organisms on Earth. The tallest plant is
a coast redwood tree in California in the United States. It stands 112
m tall. The oldest organism on Earth is thought to be the creosote bush.
This plant lives in California’s Mojave Desert. One of these small circular
bushes was found to be nearly 12,000 years old!
Plants and People
People are able to live all over the Earth
because plants make seeds that can be stored and carried to other places. This
has helped various species of plant spread to many parts of the world. Think
of wheat, rice, corn, and beans. These plants are grown all over the world.
Without these important foods, people’s lives would be very different.
The seeds of these plants are good to eat, full of nutrients, and can be made
into many different foods.
The Source of Many Things
For centuries, plants have been one of the most useful natural
resources in the world. Even today, plants are one of the most important
materials people use for building houses, making clothes, cooking, and heating.
If you take a moment to think about all the things that you use each day,
you’ll find that plants are the source of many of them. Here are some
- Breakfast cereal (rice, corn, wheat, soy)
- The cardboard box the cereal came in (wood fiber from trees)
- The chair and table you sat at for breakfast (wood from trees)
- The books and paper you use at school (wood fiber from trees)
- The air you are breathing now (oxygen from plants)
- The clothes you are wearing (cotton, linen, and hemp from plants)
More than Just a Pretty Face
Many drinks we enjoy are made from plants and their seeds – coffee,
cocoa, cola, and fruit juices such as orange juice and apple juice.
People around the world give beautiful flowers as gifts for birthdays and
weddings. Not a day goes by in which our lives are not affected by flowering
plants. Nearly all of our food comes from flowering plants. Useful products
such as rope and burlap are also made from the fibers of flowering plants.
A large number of widely used drugs, including medicines such as aspirin, come
from flowering plants. Many commercial dyes are extracted from flowering plants.
Plants and the Environment
It is impossible to think about an environment without
plants. Even environments like the hot desert or freezing polar regions have
plants. These plants have adaptations that
help them survive the harsh conditions. Plants create the base for most environments.
All of the different types of plants in an environment are commonly referred
to by scientists as “plant communities.”
Over the past few decades, people have begun to think more about the important
relationship plants have to people, animals, and the overall health of the
environment. Here are a few of the important ways plants help the environment.
Can you think of other ways?
- Trees and other plants hold the soil in place so that wind and rain don’t
create severe erosion.
- Fallen leaves and rotting wood help enrich the soil other plants need to
- Shade from trees and large bushes keeps us cool. Shade also provides places
for wildlife to live and hide.
- Trees create homes. A large old tree 40
m tall may be the home of over 1,000 species!
Plants in Peril
Rosy periwinkle is an important plant from the tropical forests of Madagascar.
The plant produces chemicals that help fight the disease cancer.
Plants are disappearing. Every year over 11.5
million hectares of tropical forest is cut and then burned to clear land
for farming and cattle grazing. This kind of change is called deforestation.
With fewer trees and other plants to convert carbon dioxide to oxygen, too
much carbon dioxide builds up. Deforestation is one cause of global
warming. The conservation of plants and forests is now something more
people and governments are beginning to discuss very seriously as one way
to protect the environment.