Lecture 1

Viruses

•Viruses are noncellular, nonliving particles and therefore are not included in the classification scheme.

•Organisms are always cellular.

The Three Domains

•Domain Archaea (Archaebacteria)

•Domain Bacteria (Eubacteria)

•Domain Eukarya (Eukaryotes)

Kingdom Archaea

•Live in extreme environments such as boiling hot (sea floor vents), or highly saline or acidic.

•Anaerobic

•Originally classified as a type of bacteria (archaebacteria).

Classifying Archaea

•Based on metabolism.

•Methanogen: methane producing

•Halophile: salt-loving

•Thermoacidophile: heat- and acid-loving

Kingdom Bacteria

•Bacteria are the oldest, structurally simplest, and the most abundant forms of life on earth.

–Abundant for over 2 billion years before the appearance of eukaryotes.

–5,000 different kinds currently recognized.

•Based primarily upon their metabolic and genetic characteristics.

•Bacterial Form

–Bacillus (Bacilli) straight and rod-shaped.

–Coccus (Cocci) spherical shaped.

–Spirillus (Spirilla) long and helical shaped.

Bacterial Diversity

•Key Classification Characteristics

–Photosynthetic or Nonphotosynthetic

–Motile or Nonmotile

–Unicellular or Multicellular

–Spore Formation or Division by Transverse Binary Fission.

Bacterial Variation

•Two processes create bacterial variation:

–Mutation

•Spontaneous errors in DNA replication.

–Genetic Recombination

•Occurs by gene transfer from one cell to another by viruses or conjugation.

Importance of Bacteria

•Largely responsible for creating atmospheric properties.

•Contribute to carbon balance.

•Nitrogen Fixation

•Industrial Processes

–Fermentation of lactose into lactic acid.

•Milk, Cheese, Yogurt

•Genetic Engineering

–Removal of environmental pollutants.

Kingdom Protista

Classifying Protists

•Protists are the most diverse of the four Kingdoms in the domain Eukarya.

–Artificial group of convenience.

–Little consensus about protist classification.

Classifying Protists

•Protozoa: Animal-like protists

•Algae: Plant-like protists

•Slime Moulds and Water moulds: Fungus-like protists

Characteristics of Protozoa

•30 000 species known

•Highly variable in form

•Most unicellular

•Lack cell walls

•Most are motile

•Some have shells

•10 000 species cause human diseases

Characteristics of Algae

•Have been present on Earth for 2 billion years +

•Simple aquatic chlorophyll-containing organisms

•Size range from single cell to 60 m in length

•Term algae covers all aquatic eukaryotes that carry out photosynthesis.

Characteristics of Slime Moulds and Water Moulds

•Difficult to classify

•Like fungi they produce spores

•Like protozoa they move and ingest food

•Like plants they have cellulose cell walls

Kingdom Fungi

A Fungus Is Not A Plant

•Differences Between Fungi and Plants

–Fungi are heterotrophs.

–Fungi have filamentous bodies.

–Fungi are capable of both sexual and asexual reproduction

The Body of a Fungus

•Fungi exist mainly in the form of slender filaments called hyphae.

–Long chains of cells joined end-to-end divided by cross-walls called septa.

•Septa rarely form complete barrier; cytoplasm freely streams in hyphae.

–Mycelium is a mass of connected hyphae.

•Grows through and penetrates substrate.

How Fungi Obtain Nutrients

•All fungi obtain food by secreting digestive enzymes and then absorbing the organic molecules produced (external digestion).

–Extensive hyphae network provides enormous surface area for absorption.

Ecology of Fungi

•Fungi and bacteria are the principal decomposers in the biosphere.

•Fungi often act as disease-causing organisms for both plants and animals.

–Agricultural Damage

Three Phyla of Fungi

•Three phyla of fungi are distinguished primarily by their sexual reproductive structures.

Phylum Zygomycota

•Smallest of three phyla. (Bread molds)

•Sexual reproduction occurs when conditions are unfavorable for growth.

•Asexual reproduction most common.

Phylum Ascomycota

•Very large group including yeasts, common molds, and morels.

•Named for reproductive structures called asci that develop during sexual reproduction.

•Asexual reproduction also occurs.

Phylum Basidiomycota

•Most familiar fungi. - Mushrooms, toadstools, puffballs, rusts, and smuts.

•Named for characteristic sexual reproductive structure, basidium.

•Cause serious damage to crops

The Imperfect Fungi

•Deuteromycota - Sexual reproductive stages have not been observed.

•Economically important genera:

•Penicillium - Penicillin

•Aspergillus - Soy Sauce