Energy Flow Through Living Systems
Florida is home to numerous zoos and aquariums, where visitors can
see exotic, rare, and native plants and animals being cared for in
controlled environments. At the Brevard Zoo in Melbourne, Florida,
nature enthusiasts can participate in self-guided kayak excursions
through the zoo’s restored Florida wetlands. On these adventures,
kayakers often see native Florida animals such as alligators,
turtles, fish, and birds of prey interacting in their natural habitat.
Those who would rather have a tour guide can kayak down the
Brevard Zoo’s human-made river that circles the Expedition Africa
exhibit. Along this route, visitors can spot giraffes, zebras, and
rhinos thriving in artificial environments that mimic those found in
Africa.
Turtles are one of the
native animals found in
Florida’s wetlands.
Other than the obvious differences in plants and animals that can
be observed on these two kayaking adventures, an aspect that
separates Wild Florida and Expedition Africa is how the
organisms obtain their food. While in Expedition Africa, visitors to
the Brevard Zoo can feed special crackers to the giraffes and
watch the rhinos being fed by the zoo staff at specified times; in
Wild Florida, there are no crackers to buy or feeding times to get
a seat for. Instead of specified feeding times, natural food
chains overlap to form a native Florida food web in the Wild
Florida ecosystem.
food web – a system
of the connected food
chains that are found
in an ecosystem
A food chain is a possible path that energy and nutrients may
take as they move through an ecosystem. A food web consists
of all the interconnected food chains that are found in that
ecosystem.The organisms in a food chain have specific roles
that create the relationships necessary for transferring energy
throughout the food web.
set of organisms get
food and how energy
is passed from one
organism to the next
food chain – a path
that shows how a
Energy Flow Through Living Systems
ecosystem – all the living organisms that share an environment
Imagine that before the establishment of taxonomy, a scientist working in Africa
writes a letter to a biologist in England, claiming that he has discovered a new
organism. It is unique, and he has never seen one before. He has named the
animal a glotchbot. The British biologist spreads the word about the glotchbot
through the scientific community, and
everyone in the community becomes
In captivity, animals do not have to
depend on hunting their prey in order
excited about this new discovery. The
scientist returns from Africa with a picture to obtain the energy they need to live
and grow. In the wild, animals are
of the glotchbot, shown on the right.
Suddenly, the scientific community loses required to compete for the energy
that is part of this food web.
all interest, and both the scientist and the
biologist are disrespected. How would a
standard system of taxonomy have changed the outcome of this scenario?
Career Corner: Taxonomist
Scientists who study taxonomy and use the classification system to identify and name organisms
are taxonomists. Taxonomists are, first and foremost, scientists. They have a fundamental
knowledge of biology or other related fields. They often have advanced degrees in zoology,
animal physiology, botany, or other life sciences. Museums, zoos, aquariums, and universities
are common places of employment for taxonomists. Here they can study DNA, environments,
and other influences that have contributed to characteristics of life. Taxonomists’ knowledge is
often used to educate others through lectures and publications about conservation of
endangered or threatened species.
Classification into Domains: Bacteria, Archaea, and Eukarya
The three domains differ fundamentally in their cellular structures and genetic makeup. The
domains are so broad that all life can be separated into just three different categories. Let’s
examine the basic differences between these three categories of life.
Domain Bacteria: This domain consists of unicellular prokaryotes. They lack a cell nucleus and
membrane-bound organelles, but they are surrounded by a thick cell wall. Bacteria can be found
nearly everywhere on Earth, including living inside human beings’ mouths and stomachs.
Bacteria are incredibly diverse. Some are free-living, while others rely on a host to survive. Many
use oxygen, while others are killed by the presence of oxygen. Like plants, some bacteria are
photosynthetic. Many bacteria cause infections, such as strep throat (Streptococcal pharyngitis),
food poisoning (Escherichia coli and Salmonella enterica), and plant wilt in sweet corn (Erwinia
stewartii). Most bacteria are beneficial and serve a necessary role in their environment. There
are a wide variety of characteristics and functions among the members of the domain Bacteria.
Energy Flow Through Living Systems
Domain Archaea: Like domain Bacteria, the members of Archaea are unicellular prokaryotes.
They also have a cell wall, but it differs in composition from those of bacteria. Archaean cell
walls lack the substance peptidoglycan, which is found in bacteria. Their cell membranes also
differ, containing unusual lipids that are not found in any other organisms on Earth. (A lipid is a
type of biomolecule; fats, oils, and waxes are examples of lipids.) One of the most distinct
features of domain Archaea is that they are able to survive in some of the most extreme
environments on Earth. Archaea have been found in the hot springs of Yellowstone National
Park in Wyoming and in deep oceanic hydrothermal vents measuring over 100°C (212°F).
Others live in environments with extremely high salinity and acidity.
Domain Eukarya: This domain differs from the others because its members’ cells contain a
nucleus and membrane-bound organelles. Most eukaryotic species are multicellular, but some
are unicellular. Domain Eukarya is quite diverse and contains the most well-known organisms.
Eukaryotes are found all over the world in a variety of environments. The domain is so diverse
that it is best to study the organisms of Eukarya in their narrower classification groups. Suppose
a group of scientists discovered a new prokaryotic organism in a highly acidic sulfur vent in
Antarctica. To which domain would the organism most likely belong?
The Four Kingdoms of Eukaryotes
Domain Eukarya is incredibly diverse. It includes organisms from daffodils to dragonflies and
orangutans to oak trees. It is divided into four kingdoms, based on the most general
characteristics.
The kingdoms are Protista, Plantae, Fungi, and Animalia. Each kingdom is further divided into
phyla, then classes, orders, and so on. The members of each kingdom have distinct enough
characteristics to allow us to begin identifying organisms.
Protista:
These ancient eukaryotes have some characteristics not shared by many other members of the
domain, including the fact that many are unicellular. Even within the kingdom, there is great
diversity. In fact, many protists are classified in this kingdom just because they do not fit in any of
the others. They vary greatly in their appearance, mobility, reproduction, and methods for
obtaining food. Some protists are even photosynthetic. Examples include many phytoplankton,
red and brown algae, and dinoflagellates.
Plantae:
Plants are very common eukaryotes. They include a wide variety of organisms with unique
characteristics and functions, as well. But there are some properties of kingdom Plantae that
they all share. Plants are multicellular organisms that are able to photosynthesize. Since plants
can use energy from the Sun to produce food, they are considered autotrophs. Plants lack
mobility and often must rely on the wind or animals to help them reproduce through crosspollination. All plants have the same basic parts, including roots, stems,
and
Energy Flow Through Living Systems
leaves. Their cells are unique from other eukaryotes because they are surrounded by a rigid cell
wall made mostly of cellulose. The cell wall gives plants structure and support, allowing them to
grow tall and expose their green leaves to the Sun for photosynthesis.
Fungi:
Fungi, such as mushrooms, are often confused with plants. They do share some similarities.
Most, for example, are multicellular, although yeasts, a type of fungus, are unicellular. Like
plants, the cells of fungi have a cell wall, which is usually made of chitin instead of cellulose.
Fungi, however, cannot produce their own food through photosynthesis, so they are called
heterotrophs. This kingdom has some characteristics that differ from any of the other eukaryotes.
A primary difference is that fungi grow long filaments, called hyphae.
Not all autotrophs get their energy from the Sun. Some autotrophs are able to make their own
food from chemicals. These organisms are called chemoautotrophs. Many species of bacteria
are chemoautotrophs, deriving energy from sources such as iron, methane, sulfur, ammonia,
and hydrogen. Organisms that get energy from the Sun are called photoautotrophs. Plants,
algae, plankton, and certain bacteria are photoautotrophs.
Trophic Levels and Energy Loss
The steps of a food chain are called trophic levels. Producers occupy the bottom trophic level,
and consumers occupy the higher trophic levels. Pyramids can be used to illustrate the amount
of energy and biomass at each trophic level. An energy pyramid shows the upward flow of
energy through a food chain. It also shows the relative amount of energy available at each
trophic level. Though the Sun supplies producers with massive amounts of energy, only about
10% of this energy is available to the consumers at the next trophic level. Where does 90% of
the energy go? Some of it is used to fuel body processes, such as growth, repair, and
reproduction. Most of it is lost to the atmosphere as heat. The more levels there are in a
pyramid, the less energy is available to the organism at the top. Biomass pyramids show the
total mass of organisms at each trophic level. Scientists usually measure biomass in grams or
kilograms of mass in a given area.
What roles do producers, consumers, and decomposers play in
moving energy through an ecosystem?
All food chains begin with energy from the Sun. Producers use this
solar energy to make sugars, through the process of photosynthesis.
Also known as autotrophs, because they can make their own
nutrition, plants, phytoplankton, and algae are typical producers in
food webs.
The producers are eaten
by consumers.
Herbivores are
consumers that eat only
Energy Flow Through Living Systems
plants, while carnivores are consumers that eat only animals.
Omnivores are consumers that eat both plants and animals. A
consumer that eats a producer is called a primary consumer.
A consumer that eats another consumer is called a secondary
consumer. Consumers that eat secondary consumers are called
tertiary consumers. All consumers are considered heterotrophic
organisms, because they depend on other organisms for their
nutrition.
Decomposers are organisms such as bacteria and fungi that break
down dead and decaying plants and animals and release nutrients
back into the soil. Decomposers can feed off of producers and
consumers.
Food chains show one of the paths that energy can travel along in
a
food web.
producer – an
organism that can make
its own food and that
serves as the primary
source of food for other
organisms
consumer – an
organism that relies on
eating other organisms
for food
decomposer – an
organism that breaks
down dead or decaying
organisms, creating
nutrients that are
released into the soil
Microscopic bacteria
Energy begins to move along
and fungi are
a food chain when a producer
decomposers that
uses photosynthesis to create
return nutrients to
the sugar it needs to carry out
the soil.
its life processes. In order to
do this, some solar energy is
used in the process. Some of
the solar energy is stored in
the plant for later use, and some is
released into the air as heat. When a consumer eats a producer, they get a
As energy moves
smaller amount of energy than what the producer initially took in from the
through an
Sun, because the consumer only has access to the energy stored in the
ecosystem, less
plant. The consumer uses some of this energy to carry out its daily activities, energy is available
some of the energy is released into the air as heat, and some is stored.
for higher-level
consumers.
If this consumer is eaten by another organism, that organism will only have
access to the energy that the consumer stored. This reduction in available energy will
continue along the food chain, with the decomposer having access to a much smaller amount
of energy than what the first producer originally took in.
Since food webs contain all the overlapping food chains in an ecosystem, it is easy to see
how incredibly important producers are to the survival of all the other organisms. Different