Chapter 5: Energy
Part 1: Food Chains, Food Webs,
and the Transfer of Energy
Autotrophs
• An organism capable of making its own
organic substances from inorganic
compounds
• Also called Producers
• Without autotrophs, there would be no
life on this planet
There are 2 types of autotrophs: The first type is the…
Photoautotrophs
A group of organisms that can
change light energy into
chemical energy (glucose) –
Photosynthesis!
– Example: green plants, algae,
cyanobacteria
Photoautotrophs
The second type of autotrophs are the …
Chemoautotrophs
Autotrophs that get their energy from
inorganic substances, such as sulfur
• Live deep down in the ocean where there is no
sunlight
• Ex. Some bacteria
Heterotrophs
• Organisms that do not make their own food
(needs to eat)
• Another term for Heterotroph is Consumer
because they consume other organisms in
order to live. Heterotrophs give off carbon
dioxide, which is required for green plants in
photosynthesis
Ex. Rabbits, Deer, Mushrooms
Heterotrophs
Heterotrophs: Herbivores
1st Order Consumer = Herbivore
Herbivores – eat ONLY plants
Ex. – Cows, Elephants, Giraffes
Heterotrophs
2nd Order Consumer
They are carnivores (eat meat)
Eats first order consumers
Ex. – Lions, Tigers, Sharks
Heterotrophs
3rd Order Consumer
eats 2nd order consumers
4th Order Consumer
eats 3rd order consumers
Heterotrophs: Omnivores
Omnivores – eat BOTH plants and
animals
Ex. – Bears and Humans
Heterotrophs: Scavengers
Scavengers – feed on the tissue of
dead organisms (both plants and
animals)
Ex. – Vultures, Crows, and Shrimp
Heterotrophs: Decomposers
Decomposers – absorb any dead material
and break it down into simple nutrients or
fertilizers
Ex. – Bacteria and Fungi (such as mushrooms
Ok, now that we know the
words…
Let’s put them together to show the flow
of energy through the ecosystem …
Food web video
Transfer of Energy
When a zebra eats the grass, it does
not obtain all of the energy the
grass has (much of it is not eaten)
When a lion eats a zebra, it does not
get all of the energy from the zebra
(much of it is lost as heat)
Transfer of Energy
No organism EVER receives all of the
energy from the organism they just ate
Only 10% of the energy from one trophic
level is transferred to the next – this is
called the 10% law
Trophic level = energy level (each step
of the food chain is a trophic level)
Transfer of Energy: The 10% Rule
– Who eats who in the food chain
– Steps along which materials & energy pass
The 10% Rule
Food Chains
The energy flow from
one trophic level to the
other is known as a
food chain
It involves one organism
at each trophic level
Food
Chain
Identify:
Source of the energy
Producer
Herbivore
Carnivore
Food
Chain
Identify:
Source of the energy
Producer
Herbivore
Carnivores
1st order consumer
2nd order consumer
3rd order consumer
Food Web
• Food Web – all of the feeding
relationships in an ecosystem
• Food webs are more complex and
involve lots of organisms
Food Web
Food Web
Notice the direction the arrow
points 
The arrow points in the direction of
the energy transfer, NOT “what ate
what”
Marine Food Web
Ecological Pyramids
4th order consumers
3rd order consumers
2nd order consumers
1st order consumers
(herbivores)
Producers
Ecological Pyramid
• An ecological pyramid shows the relationship
between consumers and producers at
different trophic levels in an ecosystem
• Shows the relative amounts of energy or
matter contained at each trophic level
• The Pyramid shows which level has the most
energy and the highest number of organisms
Ecological Pyramids
Illustrates:
Food Chain
of numbers
of biomass
of energy
Pyramid of Numbers
Biomass
• The total mass of the organic matter at each
trophic level is called biomass
• Biomass is just another term for potential
energy – energy that is to be eaten and used.
• The transfer of energy from one level to
another is very inefficient (10% Law)
Pyramid of Biomass
Energy Pyramid
Which
Which
Which
Which
level
level
level
level
has
has
has
has
the
the
the
the
most energy?
most organisms?
least organisms?
least energy?