Ecosystems: What Are They and How Do They Work? - Environmental Science - page 36

The earth's thin film of living matter is sustained by grand-
scale cycles of chemical elements.
G. E VELYN H UTCHINSON

An organism is any form of life. The cell is the ba-
sic unit of life in organisms. Organisms may consist of
a single cell (bacteria, for instance) or many cells. Look
in the mirror. You will see the result—about 10 trillion
cells divided into about 200 different types.
Organisms are classified into species, groups of
organisms that resemble one another in terms of their
appearance, behavior, chemistry, and genetic makeup.
Organisms that reproduce sexually by combining cells
from both parents are classified as members of the
same species if, under natural conditions, they can po-
tentially breed with one another and produce live, fer-
tile offspring. Scientists use a special system to classify
and name species (see Science Supplement 5 at the end
of this topic).
How many species are on the earth? We do not
know. Estimates range from 3.6 million to 100 mil-
lion—most of them microorganisms too small to be
seen with the naked eye. The best guess is that we share
the planet with 10-14 million other species. So far biol-
ogists have identified and named about 1.4 million
species, most of them insects (Figure 3-2 and Science
Spotlight, below).

This chapter describes the major components of eco-
systems and the processes that sustain them. It dis-
cusses these questions:

What is ecology?

■

What basic processes keep us and other organisms
alive?

■

What are the major components of an ecosystem?

■

What happens to energy in an ecosystem?

■

What are soils, and how are they formed?

■

What happens to matter in an ecosystem?

■

How do scientists study ecosystems?

■

KEY IDEAS
■ Life on earth is sustained by the flow of energy from
the sun, the cycling of matter or key nutrients through
the biosphere, and gravity that keeps the molecules in
the atmosphere from flying off into space.
■ Some organisms produce food; others consume
food.
■ The biodiversity found in the earth's genes, species,
ecosystems, and ecosystem processes is a vital renew-
able resource.
■ Soil supplies most of the nutrients needed for
plant growth, helps purify water, and stores carbon
that helps control atmospheric levels of carbon
dioxide.
■ Human activities are altering the flows of energy
and the cycling of key nutrients through ecosystems.

Science Spotlight: Which Species Rule
the World?
Multitudes of tiny microbes such as bacteria,
protozoa, fungi, and yeast help keep us alive.
They are everywhere and there are trillions of them.
Billions are found inside your body, on your body, in a
handful of soil, and in a cup of river water.
These mostly invisible rulers of the earth are mi-
crobes, a catchall term for many thousands of species of
bacteria, protozoa, fungi, and yeasts—most too small
to be seen with the naked eye.
Microbes do not get the respect they deserve.
Most of us view them as threats to our health in the
form of infectious bacteria or “germs,” fungi that
cause athlete's foot and other skin diseases, and proto-
zoa that cause diseases such as malaria. In reality,
these harmful microbes are in the minority.
You are alive because of multitudes of microbes
toiling away mostly out of sight. Microbes convert ni-
trogen gas in the atmosphere into forms that plants
can take up from the soil as nutrients. They also help
produce foods such as bread, cheese, yogurt, vinegar,
tofu, soy sauce, beer, and wine. Bacteria and fungi in
the soil decompose organic wastes into nutrients that
can be taken up by plants that we and most other ani-
mals eat. Without these wee creatures, we would be up
to our eyeballs in waste matter.
Microbes, especially bacteria, help purify the wa-
ter you drink by breaking down wastes. Bacteria in
your intestinal tract break down the food you eat.

3-1 THE NATURE OF ECOLOGY

What Is Ecology?
Ecology is a study of connections in nature.
Ecology (from the Greek words oikos, meaning “house”
or “place to live,” and logos, meaning “study of”) is the
study of how organisms interact with one another and
with their nonliving environment. In effect, it exam-
ines connections in nature —the house for the earth's life .
Ecologists focus on trying to understand the interac-
tions among organisms, populations, communities,
ecosystems, and the biosphere (Figure 2-3, p. 23).