Chapter 18, section 3
Interactions of living things
What is the
difference between
a food chain and a
food web?
How does energy
flow through
ecosystems?
What makes the
first link of a food
chain different
from all the rest?
Compare and
contrast producers,
consumers, and
decomposers.
Energy Flow Through Ecosystems
Most of the interactions among members of different species occur when
one organism eats another. Food contains nutrients and energy needed for
survival. Energy pass from one organism to the other. Producers take
energy from the Sun to produce Carbohydrates through a process called
photosynthesis. Consumers take energy when they feed on producers or
other consumers. When an organism dies, decomposers take leftover energy
as they break down the remains. This movement of energy is shown in food
chains and food webs.
Food Chains
A food chain is a model to illustrate how energy passes from one organism
to another organism. The arrows point in the direction energy is traveling.
The amount of available energy decreases at each level.
Food Webs
A food web is a series of overlapping food chains that exist in an ecosystem.
A food web is a more complex and complete model of how energy moves
through an ecosystem.
Ecological pyramids
Most of the energy in the biosphere comes from the Sun. Producers take in
this light energy to make (produce) an organic form of energy that can be
consumed by herbivores and then by other consumers. The bottom of the
pyramid represents the number of producers and so on as you go up the
pyramid.
Energy Pyramids
Can be described as a cross between an ecological pyramid and a food chain.
Since producers contain all the energy for an ecosystem they are at the
bottom and then the energy decreases at each level. Only about 10% of the
energy is passed on from one level to the next.
Chapter 18, section 3
Interactions of living things
How does Carbon
flow through
ecosystems?
Why is the Water
cycle such an
important part of
our ecosystem?
Why to biotic
organisms need
nitrogen?
Cycles of Matter
The law of conservation of mass states that matter on Earth is never lost or
gained, it is recycled.
Water Cycle
Water molecules on Earth constantly rise into the atmosphere and fall to the
ground. The water cycle involves the processes of evaporation,
condensation, and precipitation. Heat from the sun causes water on Earth’s
surface to evaporate (change from a liquid to a gas) rise into the atmosphere
as water vapor. As the vapor rises it encounters colder air which slow the
molecules down. The water vapor begins to condense (change from a gas to
a liquid) and these water droplets form clouds. When they get heavy enough
they fall to the Earth as some for of precipitation.
Carbon Cycle and Oxygen Cycle
All biotic organisms contain Carbon. The atmosphere contains carbon
dioxide, which is a gas. Producers “breath” in CO2 in order to make their
food and release O2 (oxygen). Consumers’ breath in O2 in order to burn the
energy we absorbed from producers and release CO2. This is how the
Carbon and Oxygen cycles are connected in our ecosystems.
Nitrogen
Nitrogen can be found in proteins and nucleic acids (DNA). Nitrogen cycle
begins as N2 is transferred from atmospheric nitrogen into a more usable
form for producers and consumers, through a process call nitrogen fixation,
by decomposers and bacteria. Then the Nitrogen moves back into the
atmosphere.