Organizing Life’s Diversity

17

The Big Idea

Evolution underlies the classification of life’s diversity.

Main Idea #1Biologists use a system of classification to organize

information about the diversity of living things.

Classification

Biologists use a system of classification to organize information about the diversity of living things.

Classification is the grouping of objects or organisms based on a set of criteria.

Early Systems of Classification

Aristotle

More than 2000 years ago, Aristotle developed the first widely accepted system of biological classification.

Aristotle classified organisms as either animals or plants.

Animals were classified according to the presence or absence of “red blood.”

Animals were further grouped according to their habitats and morphology.

Plants were classified by average size and structure as trees, shrubs, or herbs.

Aristotle’s classification system was believed to be accurate until rapid scientific exploration caused many new species to be discovered.

Using common names for so many organisms was causing problems since names varied from one location to the next.

Early Systems of Classification

Linnaeus

In an attempt to organize the system, a Swedish naturalist named Carolus Linnaeus, came up with a system that grouped organisms into hierarchical categories.

Linnaeus’s system of classification was the first formal system of taxonomy.

He used the organisms’ morphology (form and function)

His system consisted of seven levels of organization: kingdom, phylum (or division), class, order, family, genus, and species.

Early Systems of Classification

Linnaeus’s method of naming organisms, called binomial nomenclature, gives each species a scientific name with two parts.

The first part is the genus name, and the second part is the specific epithet, or specific name, that identifies the species.

Ursus americanus

(AKA the “Rebel” Black

Bear)

Rules for Scientific Names

The first letter of the genus name always is capitalized, but the rest of the genus name and all letters of the specific epithet are lowercase.

If a scientific name is written in a printed book or magazine, it should be italicized (e.g., Homo sapiens).

When a scientific name is written by hand, both parts of the name should be underlined (e.g., Homo sapiens).

After the scientific name has been written completely, the genus name will be abbreviated to the first letter in later appearances (e.g., H. sapiens).

Taxonomic Categories

The taxonomic categories used by scientists are part of a hierarchy system.

Each category is contained within another, and they are arranged from broadest to the most specific, or largest to smallest.

Each named group is called a taxa.

Main Idea #2Classification systems have changed over time

as information has increased.

What is a species?

How are things classified?

To classify a species, scientist construct patterns of descent by using

characters.These characters may morphological

or biochemical.

Morphological Characters

Shared morphological characters suggest that species are related closely and evolved from a recent common ancestor.

Analogous characters may have similar functions but different underlying construction , while homologous characters may appear similar but have differing functions.

Compare birds and dinosaurs:

Theropods have leg, wrist, hip, and shoulder structures similar to birds.

Both have hollow bones.

Some theropods may have had feathers.

Biochemical Characters

Scientists use biochemical characters, such as amino acids and nucleotides, to help them determine evolutionary relationships among species.

Scientists will also compare the DNA and RNA between species to determine how similar or different they are.

The similarity between the chromosomes of the chimpanzee, gorilla, and orangutan suggests a common ancestor.

Molecular Clocks

Scientists use molecular clocks to compare the DNA sequences or amino acid sequences of genes that are shared by different species.

The differences between the genes indicate the presence of mutations.

The more mutations that have accumulated, the more time that has passed since divergence.

Phylogenic Reconstruction

Cladistics reconstructs phylogenies based on shared characters.

A cladogram can be used to show the amount of shared characters.

The greater the number of derived characters shared by groups, the more recently the groups share a common ancestor.

Main Idea #3The most widely used biological classification system

has six kingdoms within 3 domains.

Domains & KingdomsGrouping Species

The broadest category in the classification used by most biologists is the domain.

The most widely used biological classification system has six kingdoms and three domains.

• The three domains are Bacteria, Archaea, and Eukarya.

The six kingdoms are Bacteria, Arcahea, Protisits, Fungi, Plantae, and Animalia.

Domain Bacteria

Typical BacteriaProkaryoteUnicellularMost have a cell wallMost make own food by photosynthesizingReproduce by conjugation and binary fissionUsed to make antibiotics and flavor for some foods

Domain Archaea

BacteriaExtremophilesProkaryoteUnicellularHave a cell wallMake own foodReproduce by conjugation and binary fissionRibosomal RNA holds genetic code

Domain Eukarya

Classifies all eukaryotes.

Contains kingdoms protista, fungi, plantae, and animalia.

Kingdom Protista

Uni/MulticellularSome make food via photosynthesisReproduce through conjugation, binary fission, mitosis, or meiosis.Some have a cell wall made of celluloseMost diverse kingdomAmoebas, Euglena, Diatoms, Algae

3 GroupsPlantlikeAnimallikeFunguslike

Kingdom Fungi

Uni/MulticellularCannot make its own foodReproduce through fission, fragmentation, budding, spores (sexual/asexual)Cell wall made of chitin or celluloseCan be fatal to humansMushrooms, Yeast, Lichen

Kingdom Plantae

MulticellularMakes food via photosynthesisReproduce through vegetative propagation, sexual spores, and pollinationCell wall made of celluloseMossess, grasses, trees, flowers

Kingdom Animalia

MulticellularNo cell wallDoes not make its own food.Internal/External FertilizationVertebrates/InvertebratesSymmetrical

Symmetry

AsymmetrAsymmetryy

BilateralBilateral RadialRadial

No SymmetryNo Symmetry

Can be divided Can be divided into 2 equal halves into 2 equal halves with only one linewith only one line

Grouped around a Grouped around a central point, can be central point, can be divided many ways divided many ways

to get mirror images.to get mirror images.

Types of Sexual Reproduction

Types of Asexual Reproduction