The
Importance of Plants
Close to 2.5 billion
years ago, the earth's surface and atmosphere were stable
enough to support primitive life. Single-cell organisms
began to develop in the seas that covered the planet. A
simple organism known as blue-green algae appeared and
spread across the seas. Blue-green algae used sunlight and
water to make food, and in the process, created oxygen. As
the blue-green algae grew in the earth's seas, they began to
fill the atmosphere with oxygen. The oxygen that blue-green
algae produced made it possible for other types of organisms
to develop.
Plants play the most
important part in the cycle of nature. Without plants, there
could be no life on Earth. They are the primary producers
that sustain all other life forms. This is so because plants
are the only organisms that can make their own food.
Animals, incapable of making their own food, depend directly
or indirectly on plants for their supply of food. All
animals and the foods they eat can be traced back to plants.
The oxygen we
breathe comes from plants. Through photosynthesis, plants
take energy from the sun, carbon dioxide from the air, and
water and minerals from the soil. They then give off water
and oxygen. Animals and other non-producers take part in
this cycle through respiration. Respiration is the process
where oxygen is used by organisms to release energy from
food, and carbon dioxide is given off. The cycles of
photosynthesis and respiration help maintain the earth's
natural balance of oxygen, carbon dioxide, and water.
Leaves are the main
food-making part of most plants. They capture energy from
sunlight, and turn water and carbon dioxide into sugar and
starch. This sugar and starch becomes the food that provides
plants with energy to grow, to produce flowers and seeds,
and carry on their other life processes.
Plant
Facts
Scientists believe
there are over 260,000 species of plants. Some plants are so
small they can barely be seen. Others are taller than people
or animals. One of the largest living plants on the earth
are the sequoia trees of California. Some stand over 290
feet (88 meters) high and measure over 30 feet (9 meters)
wide.
Certain
characteristics of plants set them apart from other living
things. Both plants and animals are complex organisms that
are made up of many types of cells, but plant cells have
thick, rigid walls that consist of a material called
cellulose. Animal cells do not have this material. The
cellulose enables plants to stand upright without the aid of
an internal or external skeleton.
Plants and
Their Environment
Plants require a
reasonable level of heat to grow. The most favorable
temperature at which photosynthesis takes place ranges from
near freezing to 20 to 25° C (70 to 80° F). The
rates of photosynthesis and respiration increase with rising
temperatures. Any temperatures above or below these levels
limit plant growth. The climate of a region determines what
types of plants can survive in that region.
A plant's
environment is made up of many factors. One of the most
important is the weather--sunlight, temperature, and
precipitation (rain, melted snow, and other moisture). Soil
and other plants and animals that live in the same area are
also included in the environment of a plant. All these
factors form what is called a natural community.
No two natural
communities are exactly alike, but many resemble one another
more than they differ. Botanists divide the world into
biomes--natural communities of plants, animals, and other
organisms.
Medicine
Plants provide many
useful drugs. Some of these plants have been used as
medicines for hundreds of years. The bark of the cinchona
tree was used 400 years ago to reduce fever. It is still
used to make quinine, a drug used to treat malaria and other
diseases. Another drug, called digitalis, is used in
treating heart disease. It is made from the dried leaves of
the purple foxglove plant. The roots of the Mexican yam are
used in producing cortisone, a drug useful in treating
arthritis and a number of other diseases.
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