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Scientists have developed special systems to name and organize plants and animals. These systems group living organisms on the basis of the traits they share with other organisms and on their genetic relationships with each other. Not all scientists agree on how organisms should be classified, but one widely accepted system arranges organisms into five kingdoms. In this system, organisms are grouped into the categories of kingdom, phylum, class, order, family, genus, and species, with each successive grouping containing fewer organisms that are more closely related.
The classification of the panda has been the subject of much debate. Some scientists thought that the giant panda should be classified with the red panda, which until recently was considered to be in the raccoon family. The red panda now has its own family. Both the giant panda and the red panda feed on bamboo and have long wrist bones that work like a human thumb to hold onto plants. However, by analyzing the DNA of pandas and related animals, scientists have concluded that the giant panda is more closely related to bears and have placed the panda in the bear family Ursidae. The classification of the giant panda and related animals is shown below.
Kingdom
Animalia
All members
of this kingdom are multicellular (made up of many cells) and are heterotrophic
(get their nourishment by eating other organisms). All animals require
oxygen for their metabolism.
Chordata
Chordates are all bilaterally symmetrical with distinct heads. At some point in their development, they possess a notochord (a rod-shaped supporting axis, or backbone).
Class
Mammalia
All mammals
have hair, are able to regulate their body temperature, and females can produce milk.
Carnivora
Not all members of Carnivora eat meat (pandas eat almost nothing but bamboo), but all have well-developed teeth for shredding foods. In general, these animals have strong limbs and claws and acute senses.
Family
Ursidae
Members of
the bear family have five toes on each foot and some can walk upright for
short distances. Bears are intelligent animals with a great sense
of smell.
Genus
Ailuropoda
Species
melanoleuca
The giant
panda is the only member of the genus Ailuropoda because it is
not very closely related to any other bears.
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The five kingdoms
The task of placing organisms into their correct group is not easy. One problem biologists encounter is the fact that some organisms have features that overlap multiple groups. Another problem is that there are simply so many species. For example, there are more than 3,000 species in the carrot family and at least 15,000 species of wild orchids. The five kingdoms generally accepted by researchers are:
Kingdom Animalia: This is one of the most diverse kingdoms. All of its members are multicellular, and nearly all are motile (capable of motion). All animals are eukaryotes, meaning that they have a true nucleus (an organelle that contains DNA) which is surrounded by a membrane. Sponges, insects, birds, and humans are examples of members of the animal kingdom.
Kingdom Plantae: Organisms in this kingdom are usually nonmotile and multicellular. Plants are autotrophs or "self-feeders" and have the ability to produce their own food by photosynthesis (a process in which carbon dioxide and water are converted into carbohydrates (sugars) through the use of the sun's energy). While plants are also eukaryotes, they differ from animals in that their cells are surrounded by a semirigid cell wall which gives their cells a definite shape. The plant kingdom includes trees, flowers, and mosses.
Kingdom Fungi: The fungi include molds, which are multicellular, and yeasts, which are made up of a single cell. Fungi are also eukaryotes, but they don't have the ability to photosynthesize, and they are generally non-motile. Fungi are distinct from other organisms in that they obtain their nutrients by absorbing carbon compounds from living or dead organic matter. Fungi digest their food outside of their body by secreting enzymes (exoenzymes) that break down the food into smaller compounds that the fungus can then absorb and use for energy. Examples of fungi include mushrooms, such as those you might see in the forest, and molds, which sometimes grow on old bread.
Kingdom Protista: This kingdom includes all eukaryotic organisms that are not clearly animals, plants or fungi. Many protists are single-celled, but a few are multicellular and live in colonies. Some have the ability to photosynthesize, and some are motile. The single-celled animal-like protists, called protozoans, exist all around us but usually go unnoticed because they are too small to see without a microscope. This kingdom also includes plant-like protists, such as algae and fungi-like protists, such as slime-molds.
Kingdom Monera: Members of this kingdom are all single-celled prokaryotes, meaning that they have a single chromosome of naked DNA (their DNA is not enclosed in a membrane bound organelle). The Monera kingdom is composed of all bacteria. These organisms are the structurally simplest and oldest of all living things. Bacteria live in all types of habitats, such as in our bodies, in water, and in food. One type of bacteria, the archaebacteria, can live in extreme environments, like in hot springs, and do not require oxygen to survive.
What
is a species?
The word "species"
refers to a population or populations of organisms that can produce fertile
offspring. Understanding the species concept is key when learning many
principles of biology, ecology, and genetics. Species designations sometimes
change when scientists discover, for example, that one species frequently
hybridizes, or interbreeds, with another. In this case, scientists sometimes
"lump" the two species into one. Scientists may also "split"
one species into multiple species after determining that different populations
rarely interbreed or that they have significantly different genetic make-ups.
It's all humanity's way of making sense of, and classifying, life on earth.
When
is a carnivore not a carnivore?
The classification
of the giant panda in the order Carnivora can be a little confusing. However,
this classification is based on the panda's genetic traits and anatomical
features, and not on their eating habits. There is a similar non-taxonomic
term that we use to describe what various organisms eat: "carnivore".
The term carnivore is used to describe an organism that eats animals.
The polar bear, which primarily hunts seals, is an example of a carnivorous
animal. Most other bears are omnivores, eating
both animal and plant matter. On the other hand, giant pandas are herbivores,
eating almost exclusively the grasses called bamboo. Considering their
diet and taxonomy, you could call giant pandas herbivorous carnivores.
See the table below for a brief overview of the world's eight bear species.
|
Common
Name
|
Habitat
|
Diet
|
Status
|
Continent
|
|
giant panda
|
bamboo forest | herbivore | endangered | Asia |
|
sun bear
|
tropical rainforest | omnivore | unknown | Asia |
|
sloth bear
|
tropical forests | omnivore | vulnerable | Asia |
|
Asiatic black bear
|
temperate forest | omnivore | vulnerable | Asia |
|
American black bear
|
temperate forest | omnivore | common | North America |
|
spectacled bear
|
mountains (varied) | omnivore | vulnerable | South America |
|
brown bear
|
varied | omnivore | threatened | N.A., Eurasia |
|
polar bear
|
polar ice | carnivore | not listed | NA, Eurasia |
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Tigers, Seals, and Prairie Dogs: Can you classify these animals?
With over 2 million species in the kingdom Animalia, determining the classification of an organism can be very challenging. The following exercise is designed to build on what you have learned from classifying the giant panda. In this exercise you will determine the classification of 3 additional animals: tigers, gray seals, and prairie dogs. The websites listed below provide information on each of these animals, in addition to many other animals. As you visit these websites, take notes on which phylum, order, family, genus, and species each of these organism is classified in. Also, pay close attention to the special features that characterize the animals in each group. Once you have completed your research, test your classification knowledge by taking our advanced quiz.
Classification websites:
Cats! Wild to Mild from the Natural History Museum of Los Angeles County
Animal Diversity Web from the University of Michigan's Museum of Zoology
National Aquarium in Baltimore: learn all about animals that inhabit the sea, including the gray seal.
Desert USA: read about animals that live in the desert, including prairie dogs.
And visit the Zoo's Animal Index for more information on gray seals, tigers, prairie dogs, and other animals found at the Zoo.
Just for fun:
National Wildlife Federation: card matching games, quizzes, and more
Classifying Critters: classification games from the Howard Hughes Medical Institute
National Geographic Society: lots of videos and interesting animal facts
References:
Campbell, Neil A. and Reece, Jane B. 2002. Biology, 6th edition. Pearson Education, Inc., San Francisco, CA.
Wallace, Robert A. 1997. Biology: The World of Life, 7th edition. Addison-Wesley Educational Publishers, Inc., Menlo Park, CA.
