The Living Environment

The environment consists of all the living and nonliving components that affect all
forms of life on Earth.

Ecology

Ecology is the study of the interactions between and among organisms and their
environment. An organism is any form of life.
Organisms are broken into two major types:
Prokaryotes: Organisms whose cells lack nuclei
Eukaryotes: Organisms whose cells have nuclei

Traditionally, taxonomists classified organisms into five kingdoms. Recent evolutionary

research, however, has led to a new classification system that places organisms in three
domains.

Archaea: Prokaryotic, single-celled organisms that exist in harsh environments, such as

oxygenless swamps, very salty bodies of water, and near deep-sea vents and sulfur
springs
Bacteria: Includes all other prokaryotes
Eukarya: Encompasses all eukaryotic organisms, including all members of kingdoms
Protista, Fungi, Plantae, and Animalia

Biomes and Ecosystems

A biome is a large region characterized by certain forms of life. Most biomes are determined
by their characteristic weather pattern or climate.

Major terrestrial biomes include:

Tropical rain forest: Infertile soil but heavy rainfall; dense vegetation; greatest
biodiversity of any land biome
Savannah: Open grassland with scattered trees; transitional between rainforest and
desert
Desert: Minimal precipitation; sparse vegetation; extreme daily temperature fluctuation
Chapparal: Coastal area with short evergreen shrubs; mild, rainy winter; hot, dry
summer
Temperate grassland: Abundant precipitation; rich soils; agriculturally productive
Temperate deciduous forest: Deciduous trees (have leaves that drop every winter);
warm, rainy summer; cool winter
Temperate coniferous forest: Coniferous trees (have year-round needles); warm, rainy
summer; cool winter

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 Taiga: Northern coniferous forest; long, cold winter
Tundra: Cold; little precipitation or vegetation; permafrost exists near the surface

Major aquatic biomes include:

Intertidal (littoral): Shorelines and coasts; subject to periods of wet and dry
Neritic: Shallow waters to the continental shelf
Oceanic (pelagic): Surface layers of the open ocean
Aphotic (abyssal): Deep-water areas where no sunlight penetrates
Freshwater: Ponds, lakes, rivers, etc.; tied closely to surrounding terrestrial biomes

Every biome is home to many ecosystems. An ecosystem is a characteristic community of

abiotic (nonliving) elements and biotic (living) organisms and the interactions between
them. The ecosphere consists of all the Earth’s ecosystems and is defined as all the living
organisms and the nonliving elements with which they interact.
Ecosystems may be broken down in many ways. A community consists of all of the species
living in an area; a population consists of all the organisms of one species living in an area.

Communities are not static but change over time through a process of ecological
succession or community development.
Primary succession: Colonization of an abiotic area by organisms for the first time.
Secondary succession: Recolonization of an area that has been seriously disturbed (e.g.
by a forest fire) by new organisms.
Pioneer species: The first organisms to enter (in either primary or secondary
succession).

Restoration: The recovery of a site that was disturbed by humans. Restoration may rely
on natural succession processes or may utilize more active management.

The Food Chain

In any ecosystem, matter and energy are transferred between organisms: some organisms
produce energy themselves, while others obtain it by feeding on or decomposing other
organisms. Organisms thus are classified according to their trophic level—the step that they
occupy in their ecosystem’s food chain or food web. A food chain or web details the order
of trophic interactions in an ecosystem, showing how energy is transferred between
organisms- basically who eats whom.

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Producers (autotrophs): Organisms that can make organic (carbon-containing) energy
resources (e.g., sugar) from abiotic, inorganic (non-carbon-containing) components of the
environment. Producers are considered to be in the first trophic level.
Biomass: The organic material that plants produce.
Primary productivity: The rate at which an ecosystem’s producers create biomass.
Photosynthesis: The process by which a producer converts energy from the sun, along
with carbon dioxide (CO2) and water (H2O), to sugar (glucose) and oxygen (O2).
Photosynthesis is the primary means of production in most ecosystems.
Chemosynthesis: Another, less common form of production that relies on energy from
chemicals, rather than solar energy, to create organic energy resources.

Consumers (heterotrophs): Organisms that gather energy by consuming organic material

from other organisms. Rather than perform photosynthesis or chemosynthesis, consumers
perform aerobic respiration, which converts sugar (glucose) and oxygen into carbon
dioxide and water to give them energy. Consumers are considered to be in the second or
higher trophic level.
Primary consumers: Organisms that consume mainly producers. Primary consumers are
also known as herbivores because they consume mainly plants.
Secondary consumers: Organisms that consume mainly primary consumers. Secondary
consumers are also known as carnivores because they consume mainly animals.
Tertiary consumers: Organisms that consume secondary consumers. Like secondary
consumers, tertiary consumers are carnivores.
Some organisms cannot be classified in one trophic level because they consume organisms
from multiple trophic levels.
Omnivores: Organisms that consume both producers and other consumers. Omnivores
may be in the second and higher trophic levels depending on their level of
consumption.

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 Detritivores: Organisms that consume detritus (the tissues of dead organisms, either
producers or consumers) and organic waste.
Decomposers: Organisms that break down detritus through digestion.

Energy is lost during each energy transfer from one trophic level to the next, so more
energy is needed to support higher trophic level feeders.
As a result of energy loss, there is less biomass at high trophic levels than at low trophic
levels.
Biomass pyramid: A graphical representation of biomass in an ecosystem at various
trophic levels. The pyramid shows that most of the Earth’s biomass exists in producers,
less in primary consumers, and increasingly less in higher trophic levels. In some
circumstances, the pyramid shape can vary.

Carrying capacity: The number of organisms that can be supported by the resources
available within a given area. Carrying capacity is determined by the level of primary
productivity and other factors.
Overshooting: A situation in which the number of organisms in an area exceeds the area’s
carrying capacity.
Dieback: The death of many individual organisms in an area, which occurs if carrying
capacity is exceeded. Dieback continues until the area is returned to carrying capacity.

Many types of species interactions may occur within an ecosystem.

Mutualism: Interaction between two species in which both species benefit.

Commensalism: Interaction between two species in which one species benefits while the
other experiences neither harm nor benefit.
Predation: Interaction between two species in which one species preys upon or consumes
the other.
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 Parasitism: Interaction between two species in which one species (the parasite) uses or
consumes part of another organism (the host) over some time, harming the host but
not necessarily killing it.
Interspecific competition: Competition among organisms of different species for some of
the same resources. Both species suffer from this competition.
Competitive exclusion: Principle stating that no two species will use exactly the same
resources, as the superior competitor will always outcompete and eventually kill
off the inferior competitor.
Niche: A species’ specific habitat, lifestyle, and resource usage habits. As a result of
competitive exclusion, each species must occupy its own niche.

Important Cycles in the Environment

Many important biogeochemical cycles are constantly at work in the biosphere,

recirculating nutrients and other elements through both the biotic and abiotic portions of
ecosystems.
Carbon cycle: Carbon is the primary element of life and is found in all living organisms. The
carbon cycle describes the movement of carbon through the environment.

Carbon is found in the atmosphere (primarily as CO2) and is also found dissolved in water.
Producers convert carbon dioxide, through photosynthesis, to organic (carbon-containing
compounds) that store energy.
Consumers and decomposers use these carbon compounds to produce energy, breaking
them down through respiration, thereby returning them to the atmosphere or to the
water in the form of carbon dioxide.
Carbon also can be stored in organic material, such as trees or fossil fuels.
The process of taking carbon from the environment and storing it in another form is
known as carbon sequestration.
Fossil fuels, such as coal, oil, and natural gas, are partially broken-down plant or animal
tissues that have been stored and transformed on the Earth’s surface for long
periods under high levels of heat or pressure.

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 Carbon can then be released from the above stored forms through combustion, or
burning.

Nitrogen cycle: Nitrogen is an important nutrient commonly found as a gas in the

atmosphere.

Because plants and animals cannot use the gaseous form of nitrogen easily, it must first be
converted to other usable forms by bacteria through nitrogen fixation.
Some plants, called legumes, have nitrogen-fixing bacteria known as rhizobium in their
roots. These plants take up the converted nitrogen and use it to form organic
compounds, and then animals obtain these compounds by consuming the plants.
After the plant or animal tissue dies or is discarded, the remaining nitrogen, usually in
simple forms, is converted back into atmospheric form by specialized bacteria.

Phosphorus cycle: Phosphorus is a crucial element required for energy transfer in

organisms, but much of the Earth’s phosphorus is contained in rocks.

When rocks containing phosphorous break down because of erosion or other factors, plants
then take up this phosphorus directly, and animals consume the plants.
Dissolved phosphorus and phosphorus waste eventually settle back to the ocean floor to
become rock again.

Sulfur cycle: Another mineral, sulfur, is cycled like phosphorus.

Hydrologic cycle (water cycle): Water, the most vital requirement for most organisms,
cycles through liquid, solid, and gaseous states throughout the Earth.

Water evaporates (changes from liquid to gas) from surface water on the Earth and is
taken into the atmosphere.
It then condenses (changes from gas to liquid or solid) and falls as precipitation (rain,
snow, or ice) to the Earth’s surface.
Some of this precipitated water ends up as runoff (moving from the land back into water

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 bodies), while some is taken up by plants.
Plants may either transpire the water (pass it out through their pores back into the
atmosphere), or the plants may die or be consumed, passing that water onto higher-
level organisms, detritivores, or back onto land.
In addition to being stored in surface water, much of the Earth’s water exists as
groundwater, below the Earth’s surface.

Source: http://sparkcharts.sparknotes.com/gensci/envsci/