(16) Environmental Science

What is ecology?


What Is Ecology?

CONCEPT 3-1 Ecology is a study of how organisms interact with one another and with their physical environment of matter and energy.

Cells Are the Basic Units of Life

All organisms are composed of cells: the smallest and most fundamental structural and functional units of life.

They are minute compartments covered with a thin membrane and within which the processes of life occur. The idea that all living things are composed of cells is called the cell theory and it is the most widely accepted scientific theory in biology. Organisms may consist of a single cell (bacteria, for instance) or plants and animals that contain huge numbers of cells.

Large and complex organic compounds, called macromolecules, make up the basic molecular units found in cells. Three of these molecules are polymers, formed when a number of simple organic molecules (monomers) are linked together by chemical bonds, somewhat like rail cars linked in a freight train.

The three major types of organic polymers are complex carbohydrates such as cellulose and starch that consist of two or more monomers of simple sugars such as glucose linked together; proteins formed by linking together monomers of amino acids; and nucleic acids (such as DNA) formed by linking monomers called nucleotides.

Lipids are a fourth type of macromolecule found in living organisms. A gene consists of certain sequences of nucleotides found within a DNA molecule that contain instructions, called genetic information, for making specific proteins.

These coded units of genetic information are passed on from parents to offspring during reproduction.

A chromosome is a single DNA molecule, together with a number of proteins. Each chromosome typically contains thousands of genes. Genetic information coded in your chromosomal DNA is what makes you different from an oak leaf, an alligator, or a flea, and from your parents. This genetic information makes you a member of the human species but also allows you to be a unique member of that species.

Species Make Up the Encyclopedia of Life

A species is a group of similar organisms that generally resemble one another in their appearance, behavior, chemistry, and genetic makeup. For sexually reproducing organisms, a species is a set of individuals who can mate and produce fertile offspring. Every organism is a member of a certain species. For example, all humans are members of the species Homo sapiens sapiens. Scientists use a specific system to classify and name each species.

We do not know how many species are on the earth. Estimates range from 4 million to 100 million-most of them microorganisms too small to be seen with the naked eye. The best guess is that there are 10–14 million species in the earth’s encyclopedia of life. So far biologists have identified about 1.8 million species, about 54% of them insects (Core Case Study), and know little about more than 99% of them.

Ecologists Study 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 their living (biotic) environment of other organisms and their nonliving (abiotic) environment of soil, water, other forms of matter, and energy mostly from the sun. In effect, it is a study of connections in nature.

To enhance their understanding of nature, scientists classify matter into levels of organization from atoms to the biosphere. Ecologists focus on organisms, populations, communities, ecosystems, and the biosphere (Concept 3-1). A population is a group of individuals of the same species living in a particular place at the same time. Examples include channel catfish in a pond, white oak trees in a forest, and people in a country. In most natural populations, individuals vary slightly in their genetic makeup, which is why they do not all look or act alike. This variation in a population is called genetic diversity. The place where a population or an individual organism normally lives is its habitat. It may be as large as an ocean or as small as the intestine of a termite.

A community, or biological community, consists of all the populations of different species living in a particular area. For example, the catfish in a pond usually share the pond with other fish species, and with plants, insects, ducks, and many other species that make up the community. An ecosystem is a community of different species interacting with one another and with their nonliving environment of soil, water, other forms of matter, and energy, mostly from the sun. Ecosystems can range in size from a puddle of water to an ocean, or from a patch of woods to a forest. Ecosystems can be natural or artificial (human created). Examples of artificial ecosystems are crop fields, tree farms, and reservoirs.

The biosphere consists of the parts of the earth’s air, water, and soil where life is found. In effect, it is the global ecosystem in which all living organisms exist and can interact with one another.

Relationships among cells, nuclei, chromosomes, DNA, and genes

A human body contains trillions of cells, each with an identical set of genes.

Each human cell (except for red blood cells) contains a nucleus.

Each cell nucleus has an identical set of chromosomes, which are found in pairs.

A specific pair of chromosomes contains one chromosome from each parent.

Each chromosome contains a long DNA molecule in the form of a coiled double helix.

Genes are segments of DNA on chromosomes that contain instructions to make proteins-the building blocks of life.

Which Species Rule the World?

They are everywhere. Billions can be found inside your body, on your body, in a handful of soil, and in a cup of ocean water.

These mostly invisible rulers of the earth are microbes, or microorganisms, catchall terms for many thousands of species of bacteria, protozoa, fungi, and floating phytoplankton-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 protozoa that cause diseases such as malaria. But these harmful microbes are in the minority.

We are alive because of multitudes of microbes toiling away mostly out of sight. Bacteria in our intestinal tracts help break down the food we eat and microbes in our noses help prevent harmful bacteria from reaching our lungs.

Bacteria and other microbes help purify the water we drink by breaking down wastes.

Bacteria also help produce foods such as bread, cheese, yogurt, 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 animals eat. Without these tiny creatures, we would go hungry and be up to our eyeballs in waste matter.

Microbes, particularly phytoplankton in the ocean, provide, much of the planet’s oxygen, and help slow global warming by removing some of the carbon dioxide produced when we burn coal, natural gas, and gasoline.

Scientists are working on using microbes to develop new medicines and fuels. Genetic engineers are inserting genetic material into existing microbes to convert them to microbes that can help clean up polluted water and soils.

Some microbes help control diseases that affect plants and populations of insect species that attack our food crops. Relying more on these microbes for pest control can reduce the use of potentially harmful chemical pesticides.

In other words, microbes are a vital part of the earth’s natural capital.

Critical Thinking

List three advantages that microbes have over us for thriving in the world.


Biosphere - Parts of the earth's air, water, and soil where life is found

Ecosystem - A community of different species interacting with one another and with their nonliving environment of matter and energy

Community - Populations of different species living in a particular place, and potentially interacting with each other

Population - A group of individuals of the same species living in a particular place

Organism - An individual living being

Cell - The fundamental structural and functional unit of life

Molecule - Chemical combination of two or more atoms of the same or different elements

Atom - Smallest unit of a chemical element that exhibits its chemical properties

Genetic diversity among individuals in a population of a species of Caribbean snail is reflected in the variations in shell color and banding patterns. Genetic diversity can also include other variations such as slight differences in chemical makeup, sensitivity to various chemicals, and behavior.



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