Overview of Diversity

Prokaryotes Prokaryotes are the earth’s oldest

organisms, and also the most abundant ones.

Bacteria are prokaryotes. Prokaryotes are also the most

metabolically diverse of all living organisms.

Early in the earth’s history, two structurally and metabolically different groups of bacteria

evolved. They are so different that

they are in separate kingdoms.

Archaebacteria and Eubacteria are different from each other in many ways:

Eubacteria have cell walls made of peptidoglycan, archaebacteria do not.

The plasma membranes of archaebacteria contain lipids not found in any other living thing.

The gene translation machinery of archaebacteria is similar to eukaryotes, but not eubacteria.

The genes of both eukaryotes and archaebacteria contain introns, but the genes of eubacteria do not.

The archaebacteria that survive today are methanogens, halophiles or thermophiles.Ancestral

prokaryote

Archaebacteria

Eubacteria

Origin of Eukaryotes 1.5 billion years ago, the first

eukaryotes appeared. Eukaryotes contain a membrane-

bound nucleus, internal membranes, and organelles such as mitochondria and chloroplasts.

Pelomyxa palustris is a living organism that is thought to be like the earliest eukaryotes.

Pelomyxa is like eukaryotes because it has internal membranes and is large, compared to bacteria, but it is like prokaryotes because it does not have mitochondria, and it reproduces by binary fission.

Most eukaryotes have mitochondria.

The theory of endosymbiosis proposes that mitochondria are the descendents of symbiotic, aerobic eubacteria that entered larger cells and then stayed there as symbionts.

Another characteristic that distinguishes eukaryotes from prokaryotes is division of the nucleus by mitosis.

Evolution of Sexual Reproduction Asexual reproduction is primitive

and prevalent. The oldest eukaryotes reproduce

asexually. In a stable environment, asexual

reproduction produces many identical offspring in a short time.

Asexual reproduction is also advantageous because no energy is spent finding a mate.

Sexual reproduction has advantages. Sexual reproduction provides a way to

shuffle genetic material and increase genetic variability in the offspring. Genetic diversity is the raw material of evolution.

It appears that sexual reproduction first evolved as a way to repair damaged DNA strands.

Eukaryotes have life cycles. Many protists are haploid. Animals and most plants are diploid, and produce haploid gametes.

Evolution of Multicellularity Unicellular organisms have limits on

their size. As a cell grows, it reaches a point

where there is too little surface area to meet the needs of the cell’s volume.

Multicellular organisms are made of many cells that are permanently associated with each other, each with a special function.

The advantage of multicellularity is that it allows cells to become specialized.

True multicellularity only occurs in eukaryotes.

Unicellular organisms first grouped together in colonies, without cell specialization. Later the colonies evolved into true multicellular organisms.

Unicellular

Organisms

Colonial Organisms

Multicellular Organisms

In multicellular organisms, cells are grouped into tissues, tissues into organs, organs into organ systems, and finally systems into the organism.

Cells

Tissues

Organs

Organ Systems

Organism

Classification of Living Things Linnaeus assigned two-word names

to living things. The first word is the genus, and is capitalized. The second word is the species, and is not capitalized. Both words are underlined.

Linnaeus’s system of naming living things is called binomial nomenclature.

Scientific names are universal. All scientists, regardless of the language they speak, use the same scientific names for living things.

All living things are classified in a hierarchy. Each category is based on characteristics shared by all the organisms in that category.

Kingdom

Phylum

Class

Order

Family

Genus

Species

Kingdom ArchaebacteriaCharacteristics of archaebacteria: All are unicellular prokaryotes. Cell walls lack peptinoglycan. Genes have introns. Their plasma membranes

contain lipids that are not found in any other living things.

They may be either autotrophic or heterotrophic.

They may be the ancestors of eukaryotic cells.

Living archaebacteria are divided into three groups that live in extreme environments: halophiles, thermophiles and acidophiles.

Cell wall without

peptidoglycan

Plasma membrane

Genetic material Cytoplasm with ribosomes

Kingdom EubacteriaCharacteristics of eubacteria: All are unicellular prokaryotes. Cell walls contain peptinoglycan. Genes lack introns. All reproduce asexually by binary

fission. They may be either autotrophic or

heterotrophic. Some are photosynthetic.

Extremely diversified groups Certain types may be ancestors of

mitochondria and chloroplasts.

Genetic material

Cytoplasm with ribosomes

Cell wall with peptidoglycan

Plasma membrane

Kingdom Protista Characteristics of protists: All are eukaryotic. Most are unicellular, but some are

multicellular. Protists can be autotrophic,

heterotrophic, or both at the same time.

All reproduce asexually, but some can also reproduce sexually.

Kingdom Fungi Characteristics of fungi: All are eukaryotic. Most are multicellular, but some are

unicellular. Cell walls are made of chitin, not

cellulose.

Fungi have filamentous bodies called hyphae.

They are all heterotrophs with external digestion of food. They serve as primary decomposers.

Fungi reproduce either sexually or asexually.

Kingdom Plantae Characteristics of plants: All plants are eukaryotic. All plants are multicellular. All plant cells have cell walls made of

cellulose. Most consist of two basic parts: roots

and shoots. Most plants are terrestrial and

photosynthetic autotrophs. Plants have evolved highly specialized

structures for reproduction and survival on land.

Plants reproduce sexually, although some can also reproduce asexually.

Kingdom Animalia Characteristics of animals: All animals are eukaryotes. All are multicellular with cells that

lack cell walls. Most reproduce sexually.

All are heterotrophs with internal digestion of food.

Animals have specialized tissues for movement and reaction to stimuli.

Animals inhabit nearly every kind of environment in the biosphere.