Energy Flow in Ecosystems
3.4
Energy Flow
When an animal eats a plant, energy is
transferred from plant to animal
 The same thing happens when an animal
eats another animal
 The transfer of energy through an
ecosystem can be traced
 This helps scientists see how organisms
are connected and how much energy is
transferred

Food Chains
Show how organisms in an ecosystem get
their food
 Each organism is a link in the chain and
provides food for the next link
 Always starts with a producer
 Always ends with a consumer
 Example:

Grasslands of Africa pg. 96
Acacia trees  producer
 As producers, the trees make their own
food using sunlight
 Giraffes  primary consumer
 They eat the leaves and get some of the
energy stored in them
 Lions  secondary consumer
 Lions feed on giraffes and get the energy
stored in their cells

Food Webs
Most organisms are a part of more than
one food chain
 This network of feeding relationships is
called a food web
 Eating many different foods can help a
consumer make sure it can find enough
food
 Pg. 97

Trophic Levels

Feeding level in a food chain or web

Producers make up the first trophic level

Green plants in a grassland ecosystem

Algae in an ocean ecosystem

In few ecosystems, bacteria form the first
level
Primary, Secondary, and Tertiary

The second trophic level is made up of
herbivores (primary consumers)

The third trophic level is made up of
carnivores (secondary consumers)
These feed on primary consumers

In some food chains, there is a fourth or fifth
level of consumers (tertiary consumers)
 These consumers eat other consumers

Energy Pyramids
Which are there more of: producers or
consumers? _________________
 Trophic levels form a pyramid because
there are many more producers than
primary consumers
 Producers form the bottom of the
pyramid
 There are more primary consumers than
secondary consumers

Think about it this way…
A field of grass can only support a certain
number of rabbits
 The number of rabbits can only support a
smaller number of bobcats
 The bobcats can only support an even
smaller number of cougars

Energy Transfer
pg. 99
An energy pyramid shows the amount of
energy available at each trophic level
 Each time energy is transferred, about
90% is lost
 Some is lost to heat and escapes into the
atmosphere
 Only 10% gets stored in the consumer
 As you move up the pyramid, less food
energy is available

The pyramid break down
The first trophic level is the largest and
has the most energy
 Each level above it has less energy and
fewer species
 The top level (tertiary) has the smallest
amount of energy
 This is why there are more small animals
than large animals in an ecosystem
 Food chains only have 4-5 links

Vocabulary
Food Chain
 Food Web
 Trophic Level
 Primary Consumer
 Secondary Consumer
 Tertiary Consumer
