Food Chain, Webs, and Pyramids
H. Biology
Relationship of Organisms
• Organisms are resources /
“food” for other organisms
• Food is energy which
allows the survival and
reproduction of
populations
• Food chains and food webs
show how energy is
transferred from one
organism to another
Energy Roles
• The sun is the original source of all energy!
• Producers: “Harness” energy from the sun
– Ex. plants
• Consumers: Organisms that eat something else
– Ex. animals
• Decomposers: return energy to the environment
– Ex. fungus, bacteria
Vocab You Need to Know!
• Producer - usually a green plant that produces its own food by
photosynthesis
• First-order Consumer - the organism that eats the producer
• Second-order Consumer - the organism that eats or derives
nutrients from the first-order consumer
• Herbivore - a plant eater
• Carnivore - an organism that obtains nutrients from the blood or
flesh of an animal
• Omnivore - an organism which eats both plant and animal matter
• Scavenger - an consumer that eats dead animals (e.g. crab)
• Detritivore - a consumer that obtains its nutrients from detritus
• Decomposer - an organism such as bacteria and fungi that breaks
down dead organisms and their wastes
Ecosystems
Trophic Structure
Ecosystems divided into trophic levels (feeding
levels)
Primary producers—autotrophs (mostly
photosynthetic but can be chemosynthetic)
Primary consumers—herbivores
Secondary consumers—carnivores that eat
herbivores
Tertiary consumers—carnivores that eat other
carnivores
Detrivores/Decomposers—consumers that
eat dead or decaying matter
Producers
• Plants harness energy from the sun through
photosynthesis
• Producers are the base of every food chain
– Meaning they are the source of food for all other
animals
Consumers
• 4 Types of Consumers:
– Herbivore: Eat only plants
• Ex. Cows, horses
– Carnivore: Eat only meat
• Ex. Polar bear
– Omnivore: Eat plants and animals
• Ex. Humans, grizzly bears
– Scavenger: Carnivores that feed on bodies of dead
organisms
• Ex. Vultures
Decomposer
• Decomposers break down waste and dead organisms
and return the raw materials to the environment
– Ex. Bacteria, fungi
Energy Flow through Biological
Systems
Which Way Will the Energy Flow
Go?!
Grass ------ Cow ------ Human
Plant ------ Mouse ------ Snake
Food Chain
• Food Chain – series of
organisms showing
feeding relationships.
– almost always begins with
a green plant (producer)
which is eaten by an
animal (consumer).
– The arrow means 'is eaten
by', and points to the
animal doing the eating!
– This shows the flow of
matter and energy along
the food chain.
– There are no decomposers
in a food chain.
Food Web
• Food Web is a network of interrelated food chains in a
given area
– Includes decomposers
Toxins in the Environment
Concentration of PCBs
Herring
gull eggs
124 ppm
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
• In some cases, harmful
substances persist for long
periods in an ecosystem
• One reason toxins are
harmful is that they become
more concentrated in
successive trophic levels
• In biological
magnification, toxins
concentrate at higher
trophic levels, where
biomass is lower
Biomagnification
What happens as levels of
toxins (like DDT and
mercury) as they move up
trophic levels?
• Toxin INCREASES in
concentration from one
link in a food chain to
another
– B/c they’re insoluble
Energy Pyramid
• 2nd Law of Thermodynamics: 100% of the
energy from one organism is NOT transferred
to the next
– Most of the energy (90%) is lost to the
environment / used by the organism to carry out
its life processes or it is lost to the environment
• Energy Pyramid shows the amounts of energy
that moves from one level to the next
Sample Energy Pyramid
Pyramid of Net
Productivity:
~10% of energy at
each level converted
to new biomass
CALLED 10% rule
(trophic efficiency)
LOTS OF BIOMASS
HERE
What
happens as
levels of
toxins (like
DDT) move
up trophic
levels?
Only 10% is passed on from one level to the next…the
rest is LOST (usually as heat)