Part 2:
How Ecosystems Work
Chapter 7: Aquatic Ecosystems.
Environmental Science and the Earth
Life Depends on the Sun
• The ultimate source of
energy for almost all living
things is the sun.
• Energy from the sun enters
an ecosystem when a plant
uses sunlight to make sugar
molecules in a process
called photosynthesis.
http://thundafunda.com/DESKTOPS/plogcontent/thumbs/nature/orange-sunsky/small/533-dewy-meadow-sunrise--oaklandcounty--michigan---.jpg
Photosynthesis
• Plants, algae, and some bacteria capture
solar energy and use it to drive a series of
photo-chemical reactions that convert carbon
dioxide and water into glucose and oxygen.
http://www.physicalgeography.net/fundamentals/images/photosynthe
sis.jpg
Photosynthesis
• When an animal eats a plant, some energy is
transferred from the plant to the animal.
• This energy is used to move, grow, and
reproduce.
Photo by R.L. Jowsey
The Chemical Equation for
Photosynthesis
Sunlight
6 CO2
Carbon Dioxide +
6 H2O
Water
C6H12O6
--------------------------------
Sugar
6 O2
+
Oxygen
Autotrophs are Producers
• Plants and other organisms that undergo
photosynthesis are known as Autotrophs.
• Autotrophs have cells with chloroplasts (tiny
organelles within the cell) which are the site
of photosynthesis.
• The green pigment chlorophyll is responsible
for photosynthesis.
Transfer of Energy
• When a rabbit eats a
clover plant, the rabbit
gets energy from the
carbohydrates (glucose)
the clover plant made
through photosynthesis.
http://1.bp.blogspot.com/_fBOxZ22TEZ8/S6CCNVURHTI/A
AAAAAAAACY/B_HbP71gkYk/s400/Quietland+Bunny+eati
ng+clover.jpg
Transfer of Energy
http://www.nationalgeographicstock.com/comp/MI/001/12
41723.jpg
• When a coyote eats a
rabbit, some of the
energy is transferred
from the rabbit to the
coyote.
• Rabbits and Coyotes
are heterotrophs –
also called consumers.
What Eats What?
Producer
Consumer
What Eats
What in an
Ecosystem
Energy Source
Makes its own food
through
photosynthesis or
chemical sources
Gets energy by
eating producers
and other
consumers
Examples
Grasses, ferns,
flowering plants,
trees, some
bacteria
Mice, starfish,
elephants, turtles,
humans, and ants
Types of Consumers in an Ecosystem
• Herbivores – eat autotrophs
(producers).
• Carnivores – eat other
heterotrophs (consumers).
Photo by R.L. Jowsey
http://1.bp.blogspot.com/_fBOxZ22T
EZ8/S6CCNVURHTI/AAAAAAAAACY/B
_HbP71gkYk/s400/Quietland+Bunny+
eating+clover.jpg
Types of Consumers in an Ecosystem (cont)
• Omnivore – eat both producers and
consumers.
Photo by R.L. Jowsey
• Decomposer – breaks down dead organisms in
an ecosystem and returns nutrients to the soil,
water, and air.
http://www.ucmp.berkeley.edu/fungi/basidio
/mushroomsismall.jpg
Types of Consumers in an Ecosystem
Photo by R.L. Jowsey
Energy Transfer
• Each time an organism eats another organism,
a transfer of energy occurs.
• We can trace the flow of energy as it travels
through an ecosystem by studying food
chains, food webs, and trophic levels.
Food Chains and Food Webs
• A food chain follows the flow of energy from
one organism to the next as each organism
eats another organism.
http://www.sheppardsoftware.com
Food Chains and Food Webs
• A food web includes multiple food chains
interconnected within an ecosystem.
http://www.biologycorner.com/resources/foodweb01.gif
Trophic Levels
• Each step through which energy is transferred
in a food chain is known as a trophic level.
http://images.tutorvista.com/content/environment/trophic-levelsfood-chain.jpeg
Trophic Levels
http://images.tutorvista.com/content/enviro
nment/trophic-levels-food-chain.jpeg
• Each time energy flows into
the next trophic level, some
is lost and less energy is
available to the next
trophic level.
• Only about 10% of energy
transferred is available to
the next trophic level.
Energy Pyramids
• One way to visualize the loss of energy at each
trophic level is to draw an energy pyramid.
Trophic Levels and
Energy Pyramid
http://www.etap.org/demo/biology_files/lesson6/kep26.jpg