Ch 5
How Ecosystems work
Energy in Ecosystems
• What is the source of energy for most ecosystems?
• The sun!
• What kingdom of organisms use this energy first ON
LAND?
• Plants
• What kingdom of organisms use this energy first IN
WATER?
• Protists: Algae
• Phytoplankton: small, mostly microscopic,
photosynthesizing algae that drift in the lighted part
of aquatic ecosystems
– Phyto = plant or plant-like
– Plankton = remainder of above definition
Energy Flow in Ecosystems
• What is the process plants and phytoplankton use
to produce their own food, using energy from the
sun?
• Photosynthesis
• What “food” does photosynthesis produce?
• Glucose, a simple sugar, C6H12O6
• What gas do plants use for photosynthesis?
• Carbon dioxide (CO2)
Energy Flow in Ecosystems
• What else do autotrophs need for photosynthesis?
• water
• What gas is released as a waste product of
photosynthesis?
• Oxygen (O2)
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So, putting it all together, photosynthesis
CO2 + H2O  O2 + C6H12O6
Balancing the reaction, we get
6CO2 + 6H2O  6O2 + C6H12O6
What powers this reaction?
The sun!
Energy Flow in Ecosystems
• What do we call organisms that make their
own food?
• Autotrophs
• Another term?
• Producers
• These make up the base of the food chain for
all other organisms in an ecosystem
Energy Flow in Ecosystems
• What types of organisms are most of the
producers on land?
• Plants
• What types of organisms are most of the
producers in water?
• Phytoplankton
Energy Flow in Ecosystems
• Why do we say the sun powers most (not all)
of the ecosystems on earth?
• Deep ocean vent communities have
autotrophic archaebacteria that use energy
from hydrogen sulfide.
Energy Flow in Ecosystems
• So… producers form the basis of energy of all
ecosytems
• Energy is transferred through ____________
• Eating/consumption
• What types of organisms do the consuming?
• Consumers! – duh!, or heterotrophs
• What had to come first? The autotrophs or
heterotrophs?
• Autotrophs, because heterotrophs had to
have something to eat!
Energy Flow in Ecosystems
• What process do consumers use to break
down the sugars in plants and release the
stored sun energy from them?
• Cellular respiration
• 6O2 + C6H12O6  6CO2 + 6H2O
• The exact opposite of photosynthesis
Energy Flow in Ecosystems
• Every time a consumer consumes, it gets only
10% of the original energy of the organism it
consumed
• So, _________ % is lost with each step along the
way
• Producers get 100% of the sun’s energy
• The organisms that eat producers, ____, get only
10% of that sun’s energy
• Herbivores, 1st level consumers, primary
consumers
• What do we call human herbivores?
• Vegetarians
Energy Flow in Ecosystems
• Organisms that eat the primary consumers are
called
• Secondary consumers
• Another ___ % of the sun’s energy is lost in
the transaction
• So, secondary consumers only get ____ % of
the original sun’s energy
• 1 %  (that’s us, when we eat beef, chicken
or pork)
Energy Flow in Ecosystems
• Some secondary consumers can also be
primary consumers. How?
• They eat plants and animals; i.e. steak and
salad
• Organisms that eat both plants and animals
are called
• Omnivores
Energy Flow in Ecosystems
• At the top of the food chain are organisms
that consume only other consumers
• These are called
• Carnivores
• Top carnivores are usually few and far
between in an ecosystem because there isn’t
enough of the sun’s energy left to go around
at that level
Energy Flow in Ecosystems
• Third level, or _______ consumers, get only ___%
• .1%   of the sun’s energy that went to the
producers in the ecosystem
• Most ecosystems cannot support more than 4 or
5 trophic levels
• Organisms that feed on organisms at the top level
are usually small and need small amounts of
energy, like
• Decomposers, or parasites like fleas
Energy Flow in Ecosystems
• So…, the more producers in an ecosystem, the
more of the sun’s energy can be absorbed
• And the more ___ can be supported by the
producer level
• consumers
• All food chains start with ___
• producers
Energy Pyramid
Tertiary consumer
Secondary consumer
What’s missing in this
picture?
Primary consumer
Producer
Energy Flow in Ecosystems
Tertiary consumer
Secondary consumer
Primary consumer
Producer
Each level of
consumerism is called
a TROPHIC LEVEL
Food chain vs. food web
• Food chains show one path of energy from the
sun to the last consumer (decomposer)
• Food webs show the many interconnected
paths of energy through an ecosystem
• The arrows represent ____________________
• Energy transfer from one organism to the next
Food Chain vs. Food Web
Food chain- straight line
flow of energy
Food web- complex flow
of energy made up of
many food chains