TaxonomyBio 11

Objectives

Explain how organisms are classified

Identify where different organisms should fall on the classification system

Classification

Why Classify?

To study the great diversity of organisms

biologists must give each one a name and

attempt to organize them into groups that

have meaning.

In the discipline known as Taxonomy, scientists

classify organisms and assign each a universally

accepted name.

Assigning Scientific Names

In the 18th century, scientists realized referring to

organisms by common names was confusing

Some organisms are known by many different names

depending on the language or even region

Ex. Cougar, puma, mountain lion, panther

Different organisms sometimes share a common name

Ex. In UK Buzzard = Hawk, in US Buzzard = Vulture.

Early Naming Efforts

First attempts described physical

characteristics in great detail.

Why was this a problem?

“Oak with deeply divided leaves that

have no hairs on their undersides and

no teeth around their edges”

Different scientists describe different

characteristics.

Binomial Nomenclature

In the 18th century, an botanist named

Carolus Linnaeus developed a two-word

naming system rooted in Latin.

Written in italics, fist words

CAPITALIZED, second word

lowercase.

First word = genus

Second word =species

For example: Humans belong to the

genus Homo and are of the species

sapien, the only surviving species in the

genus.

Linnaeus’s System of Classification

A hierarchical system including 7 levels. From

smallest to largest they are:

Species, genus, family, order, class, phylum, and

kingdom

Modern Evolutionary Classification

Interestingly, organisms choose their own species by who they mate with but

all other taxonomic groups were “invented” based on biological

characteristics.

Linnaeus’s system had limitations

For example: If you lived in the 18th century where would you put a dolphin?

What Characteristics are most important?

Crabs, barnacles, and limpets… let’s take a look

Evolutionary Classification

Instead of classification by physical attributes, organisms are grouped by their

evolutionary history.

Kingdoms and Domains

The scientific view was simpler in Linnaeus’s time.

Two Kingdoms: Animalia and Plantae

Then microorganisms were discovered and recognized as being significantly

different Protista.

Later, mushrooms, yeasts and molds were placed in their own kingdom Fungi.

Even later, scientists realized bacteria lacked certain cellular organelles that

other forms of life had and were given their own kingdom Monera.

This produced 5 Kingdoms: Monera, Protista, Fungi, Plantae, and Anamalia.

6 Kingdoms

In recent years, as technology and evidence increased, scientists realized that

Monera had two distinct groups that were as different as plants and animals

so it broke into two new kingdoms: Eubacteria and Archaebacteria.

This created 6 Kingdoms total.

The 3 Domain System

The most recent evolutionary trees were formed using a molecular

clock model that groups organisms according to how long they have

been evolving independently

3 Domains above Kingdom

Bacteria, Archaea, Eukarya

Domain Bacteria

Unicellular

Prokaryotic

Have thick and rigid cell walls that surround cell membrane

Contains a substance called peptidoglycan

Some need oxygen, some are killed by it.

Corresponds to kingdom Eubacteria

Domain Archaea

Also unicellular and prokaryotic

Cell walls lack peptidoglycan and contain unusual lipids not found in other

organisms

Found in extreme environments that lack oxygen

Corresponds with kingdom Archaebacteria

Domain Eukarya

Consists of all organisms that have a nucleus.

Broken into 4 Kingdoms

Protista

Fungi

Plantae

Anamalia

Dichotomous Keys

Dichotomous Keys are tools used for classification.

A series of paired statements that describe physical

characteristics.

Let’s try one!