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4.1 Roles of Living Things
1. Identify the roles of
producers, consumers, and
decomposers.
2. Explain the concept of
trophic level.
3. Infer why the number of
organisms at a given trophic
level is smaller than in the
preceding level.
Roles of Living Things

The organisms of most ecosystems gather food
in three basic ways: as producers, consumers, or
decomposers. Energy enters the ecosystem only
at the level of the producer. All other
organisms depend on the energy first captured
by the producers.
Producers

Organisms that make their own food from
inorganic molecules and energy are called
producers.

Plants are the most familiar producers. Almost all
producers capture energy from the sun and use it to
make food through photosynthesis. (The reactions
of photosynthesis use the energy from sunlight to
combine carbon dioxide and water to produce
sugars).
Photosynthesis

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6H2O + 6CO2 ----------> C6H12O6+ 6O2
http://earthguide.ucsd.edu/earthguide/diagrams/photosynthesis/photosynthesis.html
Producers

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Plants are the most important producers in
terrestrial (land) ecosystems.
In aquatic (water) ecosystems, small
photosynthetic Protists and bacteria are the
most important producers.
Consumers

Organisms that cannot make their own food are
called consumers.
All animals are consumers, as are fungi and many
Protists and bacteria.
 Consumers obtain energy by eating other organisms.

Consumers

There are four basic kinds of consumers:
1.
Organisms that eat only plants are called
herbivores. Because only eat producers, scientists
call them primary consumers. Many insects and
birds are herbivores, as are grazing animals such as
cows, buffalo, and antelope. The bodies of
herbivores are adapted to gathering, grinding, and
digesting plants.
Consumers
2.
Carnivores capture and eat herbivores or
other carnivores. Carnivores that eat primary
consumers are called secondary consumers,
and those that eat other carnivores are called
tertiary consumers.


Lions are carnivores, as are snakes, hawks, and
spiders.
The bodies of carnivores are adapted to hunting,
capturing, and eating prey.
Consumers
3. Some consumers, including human beings, are
omnivores, eating both producers and
consumers. (bears and chimpanzees)
 Omnivores act as primary, secondary, or tertiary
consumers depending on what they eat.

A person who eats a potato acts as a primary
consumer.

If the same person eats a hamburger, however, the person
acts as a secondary consumer.
Consumers
4.
Scavengers usually do not hunt living prey, but
instead feed on the bodies of dead organisms.




Scavengers will eat dead plants or feed on the bodies of
herbivores, carnivores, or anything else they find.
Like omnivores, scavengers act as secondary, tertiary, or
higher consumers depending on what they eat.
Vultures and hyenas are scavengers, as well as many insects.
Scavengers start the process by which nutrients from dead
bodies are returned to environment.
Decomposers

Bacteria and fungi that consume the bodies of
dead organisms and other organic wastes are
called decomposers.
They consume a variety of dead organic matter,
from the fallen leaves of a tree to the bodies of
herbivores and carnivores.
 Bacteria and fungi also break down the organic
matter in animal waste.
 Decomposers are crucial to the ecosystem because
they recycle nutrients from organisms back into the
environment.

Trophic Levels

Scientists call the different feeding levels of organisms
in an ecosystem trophic levels. “troph” meaning to
feed or nourish.


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A trophic level is a layer in the structure of feeding
relationships in an ecosystem.
Producers make up the first trophic level, and consumers
make up several more trophic levels. Producers are called
autotrophs, which are the sole point of entry for new energy
into the ecosystem.
Consumers called heterotrophs form the second and higher
trophic levels in the ecosystem.
Most ecosystems have three, four or five trophic levels
depending on the levels below it.
Trophic Level
Trophic Level
Trophic Levels
4.1 Homework

Many places on the ocean floor are so deep that
sunlight cannot penetrate. Because there is no
sunlight in these places, there can be no
photosynthesis. But the ocean floor still
supports an ecosystem. How is this possible.