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Chapter 5
How Ecosystems Work
Energy Flow
Energy from the sun enters an
ecosystem when a plant uses
sunlight to make sugar
molecules
Photosynthesis
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This process in which sunlight, carbon
dioxide, and water are used by plants, algae
and bacteria to make carbohydrates, oxygen,
and water
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
Energy Flow
 Organisms use carbohydrates to
carry out daily activities such as
movement, growth, and
reproduction
Producer
 Organisms that makes its own food
 Also known as:
 Autotrophs- are at the base of the food
chain
Ex. Plants, algae, and some bacteria
Consumers
 Organisms that get their energy
from eating other organisms
 Also known as: Heterotrophs
Primary Consumers
Also known as herbivores; these
organisms eat autotrophs
Ex. Insects, fish, rabbits, cows
Secondary Consumers
 Known as carnivores; these
organisms eat herbivores
Ex. Chameleon, fish, rats
Tertiary Consumer
 a carnivore which eats a carnivore
which eats a herbivore
Ex. Snake, fish, seal
Quaternary Consumer
 eat tertiary consumers; have no
natural enemies
 Hawks and a shark
Omnivore
 eat both plant and animal (primary
consumers and secondary consumers)
Ex. Bears, pigs, and humans
Decomposers
 Decomposers eat dead plants and animals
to help break down complex compounds
into simpler ones.
 fungi, bacteria,
*So how do organisms use the energy
they get?
 By a process called cellular respiration
 C6H12O6 + 6O2 = 6CO2 + 6H2O + energy (ATP)
 -during cellular respiration cells absorb oxygen and
use it to release energy from food occurs within the
mitochondria of the cell
Energy Transfer
 A way to visualize this loss of energy from
one trophic level is through an:
 energy pyramid- with the lowest trophic
level on the bottom (pg. 131)
Energy Transfer
 Also visualize the transfer of energy
through food chains and food webs
 also helps us determine which
organisms in an ecosystem depend
on other organisms to survive
Food Chain
 a sequence in which energy is
transferred from one organism to
the next as each organism eats
another
Food Web
shows many feeding
relationships that are possible in
an ecosystem
Energy loss
 Decreased amount of energy at each
trophic level results in fewer organisms
at the higher trophic levels and also
limits the number of trophic levels
 Only 10% of the energy is available at
each level
Cycling of Materials
 3 Main Cycles
 Carbon Cycle
 Nitrogen Cycle
 Phosphorus Cycle
Carbon Cycle
 Essential for proteins fats and carbohydrates
 Carbon enters ecosystem by way of plants; convert carbon
dioxide into carbohydrates
 Consumers eat the producers and get carbon from the
carbohydrates
 Some of the carbon is then released back into the air as
carbon dioxide
 Cycle (pg. 132)
Nitrogen Cycle
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Needed to build proteins
78% of gases in atmosphere
Must be altered or fixed from the atmosphere
Nitrogen-fixing bacteria accomplish this task
Excess nitrogen is released into the soil
Animals get nitrogen by eating plants
Cycle (pg. 134)
Phosphorus Cycle
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Needed for bones and teeth
Plants get it from soil and water; absorb through roots
Animals get it by eating plants or from herbivores
Added to soil and water by decomposition
Some washes off the land into the ocean
Some comes from the erosion of rocks
Some from fertilizers
Cycle (pg. 135)
Ecological Succession
 A gradual process of change and replacement of the
types of species in a community
 can take hundreds or thousands of years
 each new community that arises often makes it harder
for the previous community to survive or the new
community will not survive at all
Primary Succession
 Succession that occurs on a surface where
no ecosystem has existed before; such as on
rocks, cliffs, newly formed islands, sand
dunes,
 occurs in areas where there is no soil
Secondary Succession
 Occurs on a surface where an ecosystem
has previously existed
 occurs in ecosystems that have been
disturbed by humans, animals, or by natural
processes (fires, volcano’s, etc.)
 occurs faster than primary succession
Pioneer Species
 Plants that will colonize the area and
begin the process of ecological
succession
 make the new area habitable for other
species
Succession
 Over time, pioneer species and other species
will continue to grow and inhabit the disturbed
ecosystem
 Eventually it will form a final and stable
community:
 Climax community
Old Field Succession
 Occurs when farmland is abandoned
 First pioneer species take over (grasses and weeds)
 taller grasses and perennial plants grow in the area
(eventually killing the pioneer plants)
 over time the taller plants are taken over by taller
growing trees
 Finally, the land returns to the community that existed
before the farmers cleared it for farmland