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3–2 Energy Flow
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Producers
Where does the energy for life processes come from?
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Producers
Producers
Without a constant input of energy, living systems cannot function.
Sunlight is the main energy source for life on Earth.
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Producers
In a few ecosystems, some organisms obtain energy from a source other than sunlight.
Some types of organisms rely on the energy stored in inorganic chemical compounds.
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Producers
Only plants, some algae, and certain bacteria can capture energy from sunlight or chemicals and use that energy to produce food.
These organisms are called autotrophs.
Because they make their own food, autotrophs are called producers.
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Producers
Energy From the Sun
The best-known autotrophs harness solar energy through a process known as photosynthesis.
During photosynthesis, these autotrophs use light energy to convert carbon dioxide and water into oxygen and energy-rich carbohydrates.
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Producers
Photosynthesis is responsible for adding oxygen to—and removing carbon dioxide from—Earth's atmosphere.
Sunlight is the main energy source for life on Earth. Some types of organisms rely on the energy stored in inorganic chemical compounds. Plants use the energy from sunlight to carry out the process of photosynthesis.
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Producers
Life Without Light
Some autotrophs can produce food in the absence of light.  
When organisms use chemical energy to produce carbohydrates, the process is called chemosynthesis.
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Producers
Sunlight is the main energy source for life on Earth. Some types of organisms rely on the energy stored in inorganic chemical compounds. Other autotrophs, such as sulfur bacteria, use the energy stored in chemical bonds for chemosynthesis. In both cases, energy-rich carbohydrates are produced.
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Consumers
Consumers
Many organisms cannot harness energy directly from the physical environment.
Organisms that rely on other organisms for their energy and food supply are called heterotrophs.
Heterotrophs are also called consumers.
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Consumers
There are many different types of heterotrophs.
Herbivores eat plants.
Carnivores eat animals.
Omnivores eat both plants and animals.
Detritivores feed on plant and animal remains and other dead matter.
Decomposers, like bacteria and fungi, break down organic matter.
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12. Feeding Relationships
How does energy flow through living systems?
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13. Feeding Relationships
Energy flows through an ecosystem in one direction, from the sun or inorganic compounds to autotrophs (producers) and then to various heterotrophs (consumers).
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14. Feeding Relationships
Food Chains
A food chain is a series of steps in which organisms transfer energy by eating and being eaten.
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15. Feeding Relationships
In some marine food chains, the producers are microscopic algae and the top carnivore is four steps removed from the producer.
Small Fish
Zooplankton
Squid
Food chains show the one-way flow of energy in an ecosystem. In this marine food chain, energy is passed from the producers (algae) to four different groups of consumers.
Shark
Algae
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16. Feeding Relationships
Food Webs
Ecologists describe a feeding relationship in an ecosystem that forms a network of complex interactions as a food web.
A food web links all the food chains in an ecosystem together.
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17. Feeding Relationships
This food web shows some of the feeding relationships in a salt-marsh community.
This illustration of a food web shows some of the feeding relationships in a salt marsh.
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18. Feeding Relationships
Trophic Levels
Each step in a food chain or food web is called a trophic level.
Producers make up the first trophic level.
Consumers make up the second, third, or higher trophic levels. Primary consumers eat producers. Secondary consumers eat primary consumers. Tertiary consumers eat secondary consumers.
Each consumer depends on the trophic level below it for energy.
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Ecological Pyramids
How efficient is the transfer of energy among organisms in an ecosystem?
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Ecological Pyramids
Only about 10 percent of the energy available within one trophic level is transferred to organisms at the next trophic level.
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Ecological Pyramids
Ecological Pyramids
The amount of energy or matter in an ecosystem can be represented by an ecological pyramid.
An ecological pyramid is a diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web.
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Ecological Pyramids
Ecologists recognize three different types of ecological pyramids:
energy pyramids
biomass pyramids
pyramids of numbers
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Ecological Pyramids
0.1% Third-level consumers
Energy Pyramid:
Shows the relative amount of energy available at each trophic level.
Only part of the energy that is stored in one trophic level is passed on to the next level.
1% Second-level consumers
10% First-level consumers
Ecological pyramids show the decreasing amounts of energy, living tissue, or number of organisms at successive feeding levels. The pyramid is divided into sections that represent each trophic level. Because each trophic level harvests only about one tenth of the energy from the level below, it can support only about one tenth the amount of living tissue.
100% Producers
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Ecological Pyramids
Biomass Pyramid:
Represents the amount of living organic matter at each trophic level. Typically, the greatest biomass is at the base of the pyramid.
50 grams of human tissue
500 grams of chicken
5000 grams of grass
Ecological pyramids show the decreasing amounts of energy, living tissue, or number of organisms at successive feeding levels. The pyramid is divided into sections that represent each trophic level. Because each trophic level harvests only about one tenth of the energy from the level below, it can support only about one tenth the amount of living tissue.
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Ecological Pyramids
Pyramid of Numbers:
Shows the relative number of individual organisms at each trophic level.
Ecological pyramids show the decreasing amounts of energy, living tissue, or number of organisms at successive feeding levels. The pyramid is divided into sections that represent each trophic level. Because each trophic level harvests only about one tenth of the energy from the level below, it can support only about one tenth the amount of living tissue.
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3–2
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3–2
The main source of energy for life on Earth is
organic chemical compounds.
inorganic chemical compounds.
sunlight.
producers.
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3–2
Organisms that feed on plant and animal remains and other dead matter are
detritivores.
carnivores.
herbivores.
autotrophs.
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3–2
How does a food web differ from a food chain?
A food web contains a single series of energy transfers.
A food web links many food chains together.
A food web has only one trophic level.
A food web shows how energy passes from producer to consumer.
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3–2
In a biomass pyramid, the base of the pyramid represents the mass of
heterotrophs.
primary consumers.
producers.
top level carnivores.
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3–2
The amount of energy represented in each trophic level of consumers in an energy pyramid is about
10% of the level below it.
90% of the level below it.
10% more than the level below it.
90% more than the level below it.
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