Unit D – Living Systems
Chapter 1
The biosphere of Life
Section 1.3
The Web of Life
Roles of organisms in an ecosystem
• Producers/autotrophs
– organisms using light
energy to synthesis
sugars through
photosynthesis
– produce organic
compounds that will
serve as food for other
organisms
– rely on sunlight, water
and nutrients from the
soil and air
Roles of organisms in an ecosystem
• Consumers/heterotrophs
– organisms that rely upon
producers as a source of
food
– primary consumers
(herbivores)
• rely directly on producers for
food
• only eat green plants, algae
or plankton
Roles of organisms in an ecosystem
• Consumers
– secondary consumers
• feed on primary
consumers
– tertiary consumers
• feed on secondary
consumers
– carnivores
• organisms that kill and
eat other animals
• most carnivores are
animals, but there are a
few carnivorous plants
Roles of organisms in an ecosystem
• Other roles:
– Omnivores
• will feed on both plants and animals depending on availability and
opportunity
– Scavengers
• an animal that feeds on dead and decaying animals it did not kill
itself
– Decomposers
• organisms that break down decaying organic matter into simpler
molecules
• return organic material into inorganic nutrients in the soil
• play a critical role in the cyclic nature of the ecosystem
Energy flow in an ecosystem
• First Law of Thermodynamics
– Energy can be changed from one form to another, but it
cannot be created or destroyed.
– The total amount of energy and matter in the Universe
remains constant
• in order for an ecosystem to persist
– energy must flow from one form to another
– energy flows into an ecosystem in the form of solar energy
– most energy flows out of an ecosystem in the form of heat
Energy storage
• after the sun’s energy is converted by
photosynthesis, the energy in an ecosystem is
stored in chemical bonds
• sugars, starches, fats and proteins are complex
organic compounds that store energy in their
chemical bonds
• when an organism digests its food, it breaks
these bonds and releases usable energy
Energy pyramid
• an energy pyramid divides up all the species in
an ecosystem based on their energy source
• each step in the energy pathway corresponds
to a level on the pyramid called a trophic level
• energy conversions are never very efficient
– moving from one level to another results in most
of the energy being lost as waste
Energy pyramid
Energy pyramid
• solar energy
represents 100% of
the energy available
• much of that energy
is reflected back into
space or absorbed by
the hydrosphere
• of all the sun’s
energy, only 1.0%
used by plants in the
process of
photosynthesis
• only 0.1% is passed
on to the 1o
consumers from the
chemical bonds of
plant matter
Energy pyramid
• only about 10% of the energy available to one level is
passed on to the next level
• the rest of the energy (90%) isn’t destroyed – it is
lost to the environment as heat
• each trophic level requires a greater volume of food
to obtain the necessary energy
– example:
• a grasshopper (a 1o consumer) consumes about 0.1g of grass a day
• a peregrine falcon (a 3o consumer) consumes about 500g of other
birds a day
Other ecological pyramids
• The actual amount of
energy in each trophic level
can be difficult to measure
accurately
• A biomass pyramid
compares the dry mass of
all organisms for each level
• We specify “dry” because
water contains no usable
energy
Other ecological pyramids
• A pyramid of numbers compares
the number of individuals in each
trophic level
• bear in mind that the size of the
individual organisms matters
– typically as you move up the
pyramid the size of the
organisms increases
• the important point to note is
that it takes about a million
producers to sustain two 3o
consumers
– this puts the 3o consumers in an
ecologically fragile situation
– most endangered species are
near the top of the pyramid
Other graphic organizers
• Food chains
– show the flow of energy from producer through to all
levels of consumers
Other graphic organizers
• Food webs
– give a more detailed
account of the
interactions between
species
– food webs are made of
several food chains that
overlap or interconnect
Ecosystems in Alberta
• specific diagrams for Albertan ecosystems are
all available in your textbook
– energy pyramids  page 425-427
– food chains  page 428
– food webs  page 429-431
Worksheet questions for Ecosystem Scavenger Hunt for
Environmental Science:
1. Identify a biogeochemical cycle that is occurring in the poster. Explain which cycle
you found and what is happening. Please use at least three sentences.
2. List an example of each. The organism could be located in Washington’s ocean or
at the shore line.
– Primary Consumer– Secondary Consumer– Tertiary consumer– Decomposer– Producer3. Pick a species that you find most interesting. What do you suppose that specie’s
niche is?
4. Draw a food web of the coastal ecosystem below. Include 5 organisms, and arrows
to show how the energy is flowing.
Answers
1) Students could answer with any of the biogeochemical cycles, as long as
they provide a three sentence explanation to support their choice.
2) Producer- algae, coral, kelp
Primary consumer- some species of insects, birds, shrimp and snails
Secondary consumer- seals, some species of fish, pelican
Tertiary consumer- eagle, sea lion, killer whale
Decomposer- worms, bacteria, fungi
3) Student could answer with any species in the picture, as long as they
support their answer by describing the niche of that species.
4) Food chain example: plankton -> shrimp -> fish -> sea lion -> fungi. Any
combination of at least one organism for each trophic level is acceptable.