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Chapter 5/Section 1—
Energy Flow in Ecosystems
Where do organisms get the energy to survive?
 MOST energy originates from the sun; is captured by plants
through process of photosynthesis:
o Carbon dioxide + water + solar energy  sugar + oxygen
o
6CO2 +
6H2O + solar energy  C6H12O6 + 6O2
o The sugars/carbohydrates produced by plants can then
be eaten by animals to provide energy to move, grow &
reproduce
o When animals eat any food, its energy is released
through the process of cellular respiration (the reverse
of photosynthesis):
sugar + oxygen  carbon dioxide + water + ENERGY
 Producer (autotroph): an organism that makes its own food
 Consumer (heterotroph): an organism that gets its energy
from eating other organisms
 SOMETIMES, bacteria can produce energy without the sun
o Break down chemicals on the seafloor to release energy
and produce their own food
What eats what?
 4 different types of consumers:
o Herbivores eat producers (plants)
o Carnivores eat consumers (other animals)
o Omnivores eat both producers and consumers
o Decomposers break down dead organisms
HOW is energy transferred in an ecosystem?
 Food chain shows how energy is transferred from a single
sequence of organisms
 Food web shows multiple food chains linked together
 Each step (or link) in a food chain is called a trophic level
 Producers are at the lowest trophic level; top predators are at
the highest
 Only 10% of the energy from each trophic level is passed on
to the next level
o 90% of energy consumed by an organism gets burned off
while carrying out functions of life—moving, staying
warm, etc.
o That leaves only 10%--the part that is stored in the
organism’s body as cells and molecules (that’s what the
next level eats)
o This relationship is shown in an energy pyramid: each
level represents a trophic level, with the most energy at
the bottom (producers)