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Chapter 3
The Biosphere
Ecology

The scientific study of interactions among
organisms and between organisms and their
environment, or surroundings.
 Biosphere: contains the combined portions of
the planet in which all of life exists, including
land, water, and air.
 Interactions within the biosphere produce a
web of interdependence between organisms
and the environment in which they live.
Levels of Organization that
Ecologists Study



Species: a group of
closely related
organisms that can
breed and produce
healthy, fertile, offspring.
Populations: groups of
individuals that belong
the same species and
live in the same area.
Communities: different
populations that live
together in a defined
area.

Ecosystem: a collection
of all of the organisms
that live in a particular
place, together with their
nonliving environment.
 Biome: a group of
ecosystems that have
the same climate and
similar communities.
 Biosphere: the largest
level of study.
Ecological Methods

Scientists conduct ecological research using 3
basic approaches:

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
Observing: Ask an ecological question
Experimenting: Test the hypothesis which answers
the question.
Modeling: Many ecological events occur over long
periods of time so ecologists make models to gain
insight into complex events such as global
warming. Many models consist of mathematical
formulas based on data which allow for predictions.
Energy Flow

Sunlight is the main energy source for
life on Earth.

Less than 1% of all of Sun’s energy that
reaches the surface of the Earth is used by
living things.
Autotrophs (Producers)

Use energy from the environment (usually the
sun) to make food (organic compounds, like
glucose).


Ex. Plants, some algae, and some bacteria.
Photosynthesis: the process by which
autotrophs use sunlight to convert CO2 and
H2O into glucose (C6H12O6) and O2.
 This process is responsible for adding O2 toand removing CO2 from-Earth’s atmosphere.
Chemosynthesis

Some autotrophs can produce food in the
absence of light.
 These autotrophs rely on energy within the
chemical bonds of inorganic molecules such
as hydrogen sulfide H2S.
 When organisms use chemical energy to
produce carbohydrates, the process is called
chemosynthesis.

Ex. Bacteria living in volcanic vents and hot springs
in Yellowstone Park and other remote locations.
Heterotrophs: (Consumers)

Organisms that rely on other organisms for their
energy and food supply are heterotrophs.
 Herbivores: Cows
 Eat plants
 Carnivores: Lions
 Eat other animals
 Omnivores: Humans
 Eat both plants and animals
 Detritivores: Earthworms
 Eat dead plant and animal matter
 Decomposers: Mushrooms
 Break down organic matter
Food Chains

The energy stored by producers can be
passed through an ecosystem along a
food chain, a series of steps in which
organisms transfer energy by eating and
being eaten.
 Ex: grass → antelope → coyote
Food Webs
The feeding relationships among various
organisms in an ecosystem that form
complex interactions.
 A food web links all of the food chains in
an ecosystem together.
 Food Web Activity

Trophic Levels
Each step in a food chain or food web is
a trophic level.
 Producers make up the first trophic level.
 Consumers make up the second, third,
or higher trophic levels.
 Each consumer depends on the trophic
level below it.

Ecological Pyramids

Ecological pyramids show the decreasing
amounts of energy, living tissue, or number of
organisms at successive feeding levels.
 The pyramid is divided into sections that
represent trophic levels.
 The area of each level represents the amount
of energy or matter remaining at that level.
 3 Types:



Energy Pyramid
Biomass Pyramid
Pyramid of Numbers
Energy Pyramid

Shows the amount of energy available at each
trophic level.
 Organisms use about 10% of this energy for
life processes.
 The rest is lost as heat.
 Percentage of light or chemical energy
available at each trophic level:

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Producers (Plants): 100%
Primary consumers (cows): 10%.
Secondary consumers (humans): 1%.
Tertiary consumers (lions): 0.1% and so on.
Biomass Pyramid
Represents the amount of living organic
matter at each trophic level
 Typically the greatest biomass is at the
base of the pyramid.
 Biomass is usually measured in grams.
 A biomass pyramid represents the
amount of potential food available for
each trophic level in an ecosystem.

Pyramid of Numbers

Shows the relative number of individual
organisms at each trophic level.
Cycles of Matter
Unlike the one-way flow of energy (nonrecyclable), matter is recycled within and
between ecosystems.
 3 cycles we will talk about:

The Water Cycle
 The Carbon Cycle
 The Nitrogen Cycle

The Water Cycle

Water moves between the
ocean, atmosphere, and
land.
 Water molecules enter the
atmosphere as water
vapor when they
evaporate from the ocean,
or other bodies of water.
 During the day the sun
heats the atmosphere.
 As the warm, moist air
rises, it cools causing it to
condense into droplets
that form clouds.

When the droplets become
large enough, the water
returns to Earth’s surface
in the form of precipitation:
rain, snow, sleet, or hail.
 On land, much of the
precipitation runs along the
surface of the ground until
it enters a river or stream
that carries the runoff back
to a lake or ocean.
The Carbon Cycle

4 main processes move carbon through its
cycle:

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Photosynthesis, respiration, decomposition.
 Photosynthesis: Plants (chloroplasts)
 6CO2 + 6H2O + sunlight → C6H12O6 + 6O2
 Respiration: Plants and animals (mitochondria)
 C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP energy
Erosion and volcanic activity.
Burial and decomposition of dead organisms and their
conversion under pressure into coal and petroleum.
Mining, cutting, and burning forests and burning fossil fuels.
The Nitrogen Cycle
Organisms require nitrogen for making
amino acids, which are used to make
protein.
 Many forms of nitrogen exist on Earth:

Nitrogen gas (N2) (78% of Earth’s
atmosphere)
 Ammonia (NH3)
 Nitrate ions (NO3-)
 Nitrite ions (NO2-)

The Nitrogen Cycle
The Nitrogen Cycle (continued)

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Only certain bacteria can
use N2 gas directly.
These bacteria are found
in the roots of plants called
legumes.
These bacteria convert N2
gas to ammonia (NH3) in a
process called nitrogen
fixation.
Other bacteria convert
ammonia into nitrates
(NO3-) and nitrites (NO2-).
Once these products are
available, producers
(plants) can use them to
make proteins.

Consumers then eat the
producers and reuse the
nitrogen to make their own
proteins.
 When organisms die
decomposers turn nitrogen
to the soil as ammonia.
 Other soil bacteria convert
nitrates into nitrogen gas in
a process called
denitrification, releasing
nitrogen into the
atmosphere again.