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Energy Flow Through an
Ecosystem
Food Chains, Food Webs, Energy
Pyramids
BIO.B.4.2.1 Describe how energy flows through an
ecosystem (e.g. food chains, food webs, energy pyramids)
•Begins with the SUN
•Photosynthesis
6CO2 + 6H2O + sunlight & chlorophyll
C6H12O6 + 6O2
• The chemical reaction by which green
plants use water and carbon dioxide and
light from the sun to make glucose.
• ENERGY is stored in glucose; glucose is
stored as starch.
Organisms that can make
glucose during
photosynthesis are called
PRODUCERS or
AUTOTROPHS.
Producers use most of the
energy they make for
themselves.
Producers use cellular
respiration to supply the energy
they need to live.
6O2 + C6H12O6 --> 6H2O + 6CO2 + energy
CELLULAR RESPIRATION is the
chemical reaction that releases the
energy in glucose.
The energy that is not used by
producers can be passed on to
organisms that cannot make
their own energy.
Self-Sustained Ecosystems
Organisms that cannot make their
own energy are called
CONSUMERS or
HETEROTROPHS.
Types of Heterotrophs
• Saprophytes: plants, fungi and bacteria which live on
dead matter (AKA = decomposers).
• Herbivores : plant-eating animals
• Carnivores: meat-eating animals
• Types of Carnivores
» Predators – animals which kill and consume
their prey
» Scavengers – those animals that feed on
other animals that they have NOT killed.
• Omnivores: plant AND meat eaters
Trophic Levels
Trophic Levels = locations within a food chain:
• Primary producers: photosynthetic organisms (plants,
algae, some bacteria)
• Primary consumers: consume primary producers
• Secondary consumers: consume primary consumers
• Tertiary consumers: consume secondary consumers
Energy flows through ecosystems in one direction, typically from the
sun, through photosynthetic organisms, including green plants and
algae, through herbivores, to carnivores and finally decomposers.
SUN  PHOTOSYNTHETIC ORGANISMS 
HERBIVORES  CARNIVORES  DECOMPOSERS
Trophic Level Nutrition
• Autotrophic nutrition – Photosynthesis (from CO2 & H2O)
• Heterotrophic nutrition – Respiration (from eating food)
Most of the energy passed from
one consumer to the next is used
by the consumer.
Some of the energy is lost and
moves into the atmosphere as
heat.
Some energy is stored
and can be passed on to
another consumer.
Food Chains and Food Webs
• If an ecosystem is to be self-sustaining it
must contain a flow of energy.
• The pathways of energy through the living
components of an ecosystem are
represented by food chains and food
webs.
• Producers initiate the flow of energy by
converting solar energy (sunlight) into the
chemical energy (ATP) from food.
A food chain involves the transfer
of energy from green plants
through a series of organisms with
repeated stages of eating and
being eaten.
Food Webs:
• A group of
interconnected food
chains
• They show the
feeding relationships
in an ecosystem
Energy Transfer Is Also Modeled
Through Pyramids
•Energy Pyramids – indicates the amount of energy
transferred to each trophic level
•Biomass Pyramids – indicates the total mass for all
species at each trophic level
•Pyramid of Numbers – indicates the number of
organisms at each level
Energy Pyramids
•
•
•
•
•
•
An Energy Pyramid is a diagram
that shows the relative amounts of
energy or matter contained within
each trophic level in a food web or
food chain.
Energy Pyramid only 10% of the
energy available within one trophic
level is transferred to organisms at
the next trophic level.
There is much more energy in the
producer level of a food chain than
at the consumer levels.
Energy input usually = SUN.
Only 10% of the energy from the
sun is captured by producers.
Only 10% of the energy available
in producers is transferred to
consumers
Biomass Pyramid
Pyramid of Numbers
Which One????
• Shows an
ecosystem
containing one
tree, many
herbivores, many
omnivores, and
one carnivore
(eagle)?
Biotic Interactions In An
Ecosystem
Symbiotic Relationships
BIO.B.4.2.2 – Describe biotic interactions in an ecosystem (eg.,
competition, predation, symbiosis)
Symbiotic Relationships
• Symbiotic relationship = relationship between two organisms
• Types of Symbiotic Relationships
1. Mutualism
2. Parasitism
3. Commensalism
MUTUALISM
PARASITISM
COMMENSALISM
Mutualism
• Mutualism – a type of symbiotic relationship in which
both organisms benefit
• Examples:
– Oxpecker feeds on the ticks of rhinos.
– Acidophilus bacteria in the human digestive tract.
Bacteria get nutrients from the human and the human
digestive process is assisted.
Parasitism
• Parasitism – a type of symbiotic relationship in which
one organism benefits and the other is harmed
• Examples:
– A tick feeds off a deer’s blood.
– A tapeworm feeds off a human stripping it off valuable nutrients.
Commensalism
• Commensalism – a type of symbiotic relationship in
which one organism benefits and the other organism
does not benefit or is not harmed.
• Examples:
– Hermit crab lives in a snail shell.
– Barnacles attach themselves to whales.
Habitat vs. Niche
• Habitat: an area that provides an organism with its basic
needs for survival. (Like food, shelter, temperature, moisture,
etc...)
• Niche: the role an organism plays in its ecosystem (aka - an
organisms job)
• An organisms location in a food chain helps to
determine its niche.
• An organisms structure or shape determines its
function which influences its niche.
• Fitness: a measure of an organisms
health as determined by its ability
to produce offspring (a measure
of population size)
Competition
• Competition: occurs when two different species or
organisms living in the same environment (habitat)
and use the same limited resources such as:
»Food
»Water
»Space
»Light
»Minerals
Competition
• Competition reduces fitness (population size) of one or
both species.
• Types of competition:
– Intraspecific competition 
Competition between members
of the same species
– Interspecific competition
Competition between members
of different species
• The more similar the requirements of the organisms
involved, the more intense the competition.
• Two organisms can share the same HABITAT but not
occupy the same NICHE!
Predator-Prey Relationships
• Predation: one species feeds on another
• Predation will improve the fitness of the
predator, but reduces the fitness of the prey.
Ecological Roles
• Specialist: organism that eats a particular type of food and/or lives
in a specific environment (small range)
• Examples:
– Koalas
– Cactus
– Giraffes
• Generalist: organism that eats many types of food or lives in a wide
range of environments
• Keystone Species: a species that is at the center of a food web and
has an unusually large impact on its ecosystem
– American Alligator: makes “alligator holes” in
the Everglades that serve as a source of food
and water for other animals during droughts
Recycling Matter in Ecosystems
Water Cycle, Carbon Cycle, Oxygen Cycle
And Nitrogen Cycle
BIO.B.4.2.3 – Describe how matter recycles
through an ecosystem (ie. Water cycle, carbon
cycle, oxygen cycle, and nitrogen cycle)
Recycling Matter
• In a self-sustaining ecosystem, materials must
be cycled between organisms and the abiotic
environment…this is where processes like
photosynthesis and cellular respiration play
important roles.
• Materials constantly need to be recycled from
the living and non-living environment so that
materials can be reused by different living
organisms in order to maintain biogeochemical
cycles and hydrologic cycles like the water cycle,
oxygen cycle, carbon cycle and nitrogen cycle..
Water Cycle
Involves the following processes:
•Precipitation
•Evaporation
•Condensation
•Transpiration
Water Cycle Terminology
• Evaporation – water separates into hydrogen and oxygen molecules
due to a rise in temperature
• Condensation – water collects due to a drop in temperature
• Precipitation – water falls from the clouds due to changes in
temperature and pressure
• Surface Water and Groundwater – water collects or runs from one
region to another
• Transpiration – plants draw water up from
the ground and release it through their
stoma (openings) in the leaves
Carbon
Cycle
Carbon is added to the atmosphere (CO2) by the following:
•Combustion - Burning of Fossil Fuels (exhaust)
•Respiration – From ALL organisms, aquatic and terrestrial
•Natural Events – Volcanism
Carbon is removed from the atmosphere (CO2) by the following:
•Photosynthesis – From aquatic and terrestrial organisms
Carbon is transferred between the earth and living organisms by:
•Consumption - Carbon is transferred from plants to animals
through organic molecules like carbs, lipids and proteins.
In other words….Carbon passes through food chains and food webs as one
organism consumes the next.
•Decomposition – Carbon molecules from dead organisms form fossil fuels.
Carbon Cycle
Oxygen Cycle
•
•
•
Oxygen is added to the atmosphere by the following:
– Photosynthesis - From aquatic and terrestrial organisms
Oxygen is removed from the atmosphere:
– Respiration - From ALL organisms, aquatic and terrestrial
– Decomposition – Oxygen is needed to allow this process to continue
– Combustion – Oxygen is required to fuel the fire!
Oxygen is also found in organic compounds in living things:
– Carbohydrates
– Lipids (Fats)
– Proteins
Oxygen Cycle
Nitrogen Cycle
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•
•
•
•
•
•
All life requires nitrogen-compounds like amino acids, proteins & nucleic acids.
The majority of nitrogen, 79%, is supplied by the air, but the nitrogen in the air is
not a usable form for most organisms.
Nitrogen fixation = process of bacteria converting nitrogen gas (N2) into usable
nitrogen compounds. Usable forms of nitrogen include:
– Nitrates (NO3-)
– Nitrites (NO2-)
– Ammonia (NH3)
Different types of bacteria help us convert nitrogen into different forms:
– Nitrification = converts ammonia into nitrites OR nitrites into nitrates
– Denitrification = converts nitrates back into nitrogen gas
Plants get usable nitrogen compounds
from nitrogen fixing bacteria. Animals get
their nitrogen by consuming plants.
Decomposing plant and animal matter
supplies a source of nitrogen.
Nitrogen fixing
Animal waste also provided a source
bacteria forming
of nitrogen.
root nodules on
legumes.
Nitrogen Cycle
Nitrogen Gas  Ammonia  Nitrates/Nitrites  Nitrogen Gas
A
B
C
A = Nitrogen Fixation
B = Nitrification
C = Denitrification