Energy and Matter: Flows, Cycles, & Conservation: Feature 1

Energy and Matter: Flows,
Cycles, & Conservation

Energy and matter are essential to the function of any
system. Energy is what powers processes and matter
is they work on and change. Without a continuous flow
of matter and energy the system will cease to function.
Some systems conserve matter by cycling and
recycling continuously. If these systems also have
renewable or inexhaustible source of energy, they
become sustainable..
FEATURE 1
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FEATURE 3
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ECOSYSTEM ENERGY
FLOW
Nearly all of the energy that drives ecosystems ultimately
comes from the sun. Solar energy, which is an abiotic factor,
by the way, enters the ecosystem through the process of
photosynthesis. You can learn more than you want to know
about this process in the unit on photosynthesis. Or, you could
just chat with your local botanist. Everyone has one, right?
The organisms in an ecosystem that capture the sun’s
electromagnetic energy and convert it into chemical energy
are called producers. Not to be confused with these
Producers.
The name is appropriate because producers make the

carbon-based molecules, usually carbohydrates, that the rest
of the organisms in the ecosystem, including you, consume.
Producers include all of the green plants and some bacteria
and algae. Every living thing on Earth literally owes its life to
the producers. The next time you see a plant, it wouldn’t be a
bad idea for you to thank it for its services...which, as you will
learn in other units, go way beyond just supplying you with
food.
After a producer has captured the sun’s energy and used it to

grow yummy plant parts, other organisms come along and
greedily gobble it up. These primary consumers, as they are
called, exclusively feed on producers. If these consumers are
human, we call them vegetarians. Otherwise, they are known
as herbivores.
Primary consumers only obtain a fraction of the total solar

energy—about 10%—captured by the producers they eat. The
other 90% is used by the producer for growth, reproduction,
and survival, or it is lost as heat. You can probably see where
this is going. Primary consumers are eaten by secondary
consumers. An example would be birds that eat bugs that eat
leaves. Secondary consumers are eaten by tertiary
consumers. Cats that eat birds that eat bugs that eat leaves,
for instance.
At each level, called a trophic level, about 90% of the energy

is lost. What a shame. So, if a plant captures 1000 calories of
solar energy, a bug that eats the plant will only obtain 100
calories of energy. A chicken that eats the bug will only obtain
10 calories, and a human that eats the chicken will only obtain
1 calorie of the original 1000 calories of solar energy captured
by the plant. When you think about this way, it would take 100
1000-calorie plants—those would be enormo plants, by the
way—to produce a single 100-calorie piece of free-range
chicken. You are now recalling all of the plants you have ever
forgotten to water in your life and feeling really, really terrible
about it, aren't you?
The relationships among producers, primary consumers,

secondary consumers, and tertiary consumers is usually
drawn as a pyramid, known as an energy pyramid, with
producers at the bottom and tertiary consumers at the top.
You can see from the example above why producers are at
the bottom of this pyramid. It takes a lot of producers for
higher-trophic-level consumers, like humans, to obtain the
energy they need to grow and reproduce.
This is the answer to the great mystery as to why there are so

many plants on Earth. We will even spell it out for you
because it is so important to understand: there are so many
plants on Earth because energy flow through ecosystems is
inefficient. Only 10% of the energy in one trophic level is ever
passed to the next. So, there you have it. We hope you feel
fulfilled.
In addition to energy pyramid diagrams, ecosystem ecologists

sometimes depict the relationship between trophic groups in a
linear way, with arrows pointing from one organism to another.
If there is only one producer, one primary consumer, one
secondary consumer, and one tertiary consumer, this linear
diagram is called a food chain. Food chains help ecologists
and students visualize the interactions between organisms in
an ecosystem. As always seems to be the case, it isn’t ever
that simple. In fact, trophic interactions among organisms in
an ecosystem are often really complex. It’s rare that an
ecosystem only has one species at each trophic level.
Usually, there are multiple producers that are eaten by
multiple primary consumers. Some consumers eat different
kinds of producers. Likewise, secondary consumers
sometimes eat producers as well as primary consumers.
These are known as omnivores.
These complex relationships are often depicted—if they can

be figured out, that is—in a diagram called a food web. These
diagrams can become messy indeed, depending on the size
of the ecosystem and the number of interactions among
trophic groups. If you like puzzles and biology, though,
ecosystem ecology is the field for you.
Ecologists use food webs to better understand the intricate
workings of the ecosystems they study. Understanding exactly
who is eating whom can provide valuable information for
conservation biologists as well. Such knowledge can aid in
restoration efforts, species recovery projects, and
preservation efforts, just to name a few instances. In any
case, uncovering food webs goes a long way to
understanding the first half of an ecosystem, the community.
Brain Snack
Most of our energy comes from domesticated animals and

plants, but we are not the only organisms on the planet that
farm. Insects, such as the fungal ants, feeding leaf clippings to
a special symbiotic fungus and protect it from invasive
pathogens. The ants tendto their fungus just as humans tend
to their gardens. You can watch an ant colony tend to their
fungus in real time here.
Illustrations of the cycles of energy in an

ecosystim

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Energy and Matter: Flows,

Cycles, & Conservation

The name is appropriate because producers make the

After a producer has captured the sun’s energy and used it to

Primary consumers only obtain a fraction of the total solar

At each level, called a trophic level, about 90% of the energy

The relationships among producers, primary consumers,

This is the answer to the great mystery as to why there are so

In addition to energy pyramid diagrams, ecosystem ecologists

These complex relationships are often depicted—if they can

Most of our energy comes from domesticated animals and

Illustrations of the cycles of energy in an

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