CLASSIFICATION

Chapter 18

Species

A species is a population of organisms that share similar characteristics and can breed with one another and produce fertile offspring.

Biologist have identified approximately 1.5 million species.

It has been estimated that there are between 2 and 100 additional species that have yet to be discovered.

Why classify?

To study to the great diversity of organism, each organism must be named.

Living things must also be organized into groups that have biological meaning.

To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.

Assigning scientific names

The problem - Common names vary among languages and even among regions within a single country.

What is a buzzard?

Taxonomy

In the discipline known as taxonomy, scientists classify organisms and assign each organism a universally accepted name.

By using a scientific name, biologists can be certain that everyone is discussing the same organism.

When taxonomists classify organisms, they organize them into groups that have biological significance.

Taxonomy

Binomial Nomenclature Two-word naming

system. In binomial

nomenclature, each species is assigned a two-part scientific name.

The scientific name is always written in italics. The first word is

capitalized, and the second word is lowercased.

The first part of the name identifies the genus to which the species belongs; the second part identifies the species within the genus.

elk (Cervus canadensis) mountain lion (Felis

concolor ) cactus (Peromyscus

eremicus)

Linnaeus's System of Classification Carolus Linnaeus Hierarchial system of

classification. Includes seven

taxonomic categories (smallest to largest): Species Genus Family Order Class Phylum Kingdom

Taxonomic nomenclature

Each level is called a taxon (plural : taxa), or taxonomic category.

Organisms belonging to the same kingdom are not necessarily very similar.

Organisms belonging to the same species are very similar and can produce offspring.

Genus and species are the smallest categories.

What do the scientific names of the polar and grizzly bears tell you about their similarity to each other?

Ursus arctos Ursus maritimus

They do not belong to the same species. The shared genus Ursus indicates the two species are closely related

Ailuropoda melanoleuca

Taxonomy categories

Genera that share the same characteristics are grouped in a large category, the family.

Similar families are grouped into a larger category, the order.

Similar orders are grouped into a larger category, the class.

Several different classes make up a phylum. A phylum can include many different organisms that share important characteristics.

The kingdom is the largest and most inclusive taxonomic category.

18.1 – Key questions

How are living things organized for study?

To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.

Why do scientists avoid using common names when discussing organisms?

By using a scientific name, biologists can be certain that everyone is discussing the same organism.

18.1 – Key questions

What is binomial nomenclature? In binomial nomenclature, each species

is assigned a two-part scientific name. The scientific name is always written in italics. The first word is capitalized, and the second word is lowercased.

Kingdoms

Originally, two kingdoms – Animalia and Plantae.

Scientists soon realized that microorganisms were significantly different from organisms in the two original kingdoms. Kingdom Protista established.

Then, the mushrooms, yeasts, and molds were separated from the plants and placed in their own kingdom, Fungi.

Kingdoms

Later still, scientists realized that bacteria lack the nuclei, mitochondria, and chloroplasts found in other forms of life.

Therefore, they were placed in another new kingdom, Monera.

This process produced five kingdoms—Monera, Protista, Fungi, Plantae, and Animalia.

Kingdoms

Biologists came to recognize that the Monera were composed of two distinct groups.

Some biologists consider the differences between these two groups to be as great as those between animals and plants.

As a result, the Monera have been separated into two kingdoms, Eubacteria and Archaebacteria, bringing the total number of kingdoms to six.

Kingdoms

Five kingdom system of classification: Animalia Plantae Protista Fungi Monera

Six-kingdom system of classification: Eubacteria Archaebacteria Protista Fungi Plantae Animalia.

Domains

Molecular analyses have given rise to a new taxonomic category that is now recognized by many scientists.

The domain is a more inclusive category than any other—larger than a kingdom.

The three domains are Domain Eukarya, which is composed of protists,

fungi, plants, and animals; Domain Bacteria, which corresponds to the kingdom

Eubacteria; Domain Archaea, which corresponds to the kingdom

Archaebacteria.

Domains

Domain Bacteria

Members of the domain are unicellular and prokaryotic.

Their cells have thick, rigid cell walls that surround a cell membrane.

The cell walls contain a substance known as peptidoglycan.

The domain Bacteria corresponds to the kingdom Eubacteria.

Peptidoglycan

Domain Bacteria

These bacteria are ecologically diverse, ranging from free-living soil organisms to deadly parasites.

Some photosynthesize, while others do not.

Some need oxygen to survive, while others are killed by oxygen.

These are "true" bacteria ubiquitous in nature.

They are found practically in all the environments, at all the attitudes and depths, in extremely low and high temperature, in fresh as well as in marine water and in bodies of plants and animals both living and dead.

Domain Bacteria

Domain Archaea

Most archaeans don't look that different from bacteria under the microscope, and that the extreme conditions under which many species live has made them difficult to culture, so their unique place among living organisms long went unrecognized.

However, biochemically and genetically, they are as different from bacteria as you are.

Although many books and articles still refer to them as "Archaebacteria", that term has been abandoned because they aren't bacteria -- they're Archaea.

Domain Archaea

Unicellular and prokaryotic. Live in some of the most

extreme environments you can imagine—volcanic hot springs, brine pools, and black organic mud totally devoid of oxygen.

Many of these bacteria can survive only in the absence of oxygen.

Cell walls lack peptidoglycan, and their cell membranes contain unusual lipids that are not found in any other organism.

Domain Eukarya

The domain Eukarya consists of all organisms that have a nucleus.

It is organized into the four remaining kingdoms of the six-kingdom system: Protista, Fungi, Plantae, and Animalia,

The distinction recognizes the common traits that eukaryotic organisms share, such as nuclei, cytoskeletons, and internal membranes.

Domain Eukarya

Kingdom Protista Eukaryotic organisms that cannot be classified as animals,

plants, or fungi. Of the six kingdoms, Protista is the least satisfying

classification, because its members display the greatest variety.

Most protists are unicellular organisms, but some, such as the multicellular algae, are not.

Some protists are photosynthetic, while others are heterotrophic.

Some share characteristics with plants, others with fungi, and still others with animals.

Giardia Volvox Paramencium Diatoms

Domain Eukarya

Kingdom Fungi Members of the kingdom

Fungi are heterotrophs. Most feed on dead or

decaying organic matter. Unlike other heterotrophs,

fungi secrete digestive enzymes into their food source. They then absorb the smaller food molecules into their bodies.

The most recognizable fungi, including mushrooms, are multicellular.

Some fungi, such as yeasts, are unicellular.

Domain Eukarya

Kingdom Plantae Members of the kingdom Plantae

are multicellular organisms that are photosynthetic autotrophs.

They carry out photosynthesis. Plants are nonmotile—they

cannot move from place to place. They also have cell walls that

contain cellulose. The plant kingdom includes

cone-bearing and flowering plants as well as mosses and ferns.

Although older classification systems regard multicellular algae as plants, in this book we group algae with the protists.

Domain Eukarya

Kingdom Animalia Members of the

kingdom Animalia are multicellular and heterotrophic.

The cells of animals do not have cell walls.

Most animals can move about, at least for some part of their life cycle.

Key questions

What are the six kingdoms of life as they are now identified? The six-kingdom system of classification includes the kingdoms Eubacteria, Archae, Protista, Fungi, Plantae, and Animalia.

 Why was the kingdom Monera divided into two separate kingdoms? Biologists recognized that the Monera were composed of two distinct groups of organisms. The two groups are as different as plants are to animals.

Key questions

How are members of the kingdom Fungi different from members of the kingdom Plantae? Fungi are heterotrophs and secrete digestive enzymes into their food source. They then absorb the smaller food molecules into their bodies. Fungi are unicellular. Plantae are multicellular organisms that are photosynthetic autotrophs. In other words, they carry out photosynthesis.

 How are members of the kingdom Fungi similar to members of the kingdom Plantae? Some fungi are multicellular like plantae organisms.