LIFESCI 1 Study Guide - Final Guide: Keystone Species, Intraspecific Competition, Ecology
Chapter 29 – Bacteria and Archaea
Bacteria and Archaea –
• Form two of the three largest branches on the tree of life
• The third major branch or domain consists of eukaryotes and is called the Eukarya
• Are unicellular and prokaryotic – meaning that they lack a membrane-bound nucleus
• Bacteria
o Have a unique compound called peptidoglycan in their cell walls
• Archaea
o Have unique phospholipids in their plasma membranes – the hydrocarbon tails of the
phospholipids are made from isoprene
o Archaea are more closely related to eukaryotes than they are to bacteria
Biological impact –
• The lineages in the domains Bacteria and Archaea are ancient, diverse, abundant, and
ubiquitous
o Abudance: in terms of the total volume of living material on our planet, bacteria and
archaea are dominant life-forms
• Extreme environments
o Bacteria or archaea that live in high-salt, high-temperature, low-temperature, or high-
pressure habitats are extremophiles
o Extremophiles have become a hot area of research
▪ Origin of life: likely that the first forms of life lived at high temperature and
pressure in environments that lacked oxygen
▪ Extraterrestrial life: used as model organisms in the search for extraterrestrial
life. If bacteria and archaea can thrive in extreme habitats on Earth, cells might
possibly be found in similar environments on other planets or moons of planets
▪ Commercial applications: for enzymes
• Medical Importance
o Bacteria that cause disease are pathogenic
▪ Pathogenic forms come from several different lineages in the domain Bacteria
▪ Pathogenic bacteria tend to affect tissues at the entry points to the body such as
wounds or pores in the skin, the respiratory and gastrointestinal tracts, and the
urogenital canal
• Koch’s postulates
o Established a link between a particular species of bacterium and a specific disease by
proposing four criteria:
▪ The microbe must be present in individuals suffering from the disease and
absent from healthy individuals
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• i.e. Bacillus anthracis present in the blood of cattle suffering from
anthrax but not from healthy individuals
▪ the organism must be isolated and grown in a pure culture away from the host
organism
▪ if organisms from the pure culture are injected into a healthy experimental
animal, the disease symptoms should appear
▪ the organism should be isolated from the diseased experimental animal, again
grown in pure culture, and demonstrated by its size, shape, and color to be the
same as the original organism
Enrichment Cultures
• One classical technique for isolating new types of bacteria and archaea is called enrichment
culture
o Based on establishing a specified set of growing conditions
o Cells that thrive under the specified conditions increase in numbers enough to be
isolated and studied in detail
Diversification of Bacteria and Archaea
• Morphological Diversity
o Size: Bacterial cells range in size from the smallest of all free-living cells – bacteria called
mycoplasmas – to the largest bacterium known, Thiomargarita namibiensis
o Shape: Bacterial cells range in shape from filaments, spheres, rods, and chains to spirals
o Motility: Many bacterial cells are motile; swimming movements powered by flagella
o Cell-wall composition:
▪ Gram-positive: have a plasma membrane surrounded by a cell wall with
extensive peptidoglycan; purple
▪ Gram-negative: have a plasma membrane surrounded by a cell wall that has two
components – a thin gelatinous layer containing peptidoglycan and an outer
phospholipid bilayer; pink
• Metabolic Diversity
o The most important thing to remember about bacteria and archaea is how diverse they
are in the types of compounds they can use as food
o Bacteria and archaea produce ATP in three ways
▪ Phototrophs use light energy to excite electrons. ATP is produced by
photophosphorylation
▪ Chemoorganotrophs oxidize organic molecules with high potential energy such
as sugars. ATP may be produced by cellular respiration – with sugars serving as
electron donors – or via fermentation pathways
▪ Chemolithotrophs oxidize inorganic molecules with high potential energy such
as ammonia or methane. ATP is produced by cellular respiration and inorganic
compounds serve as the electron donor
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o Bacteria and archaea obtain building-block compounds with carbon-carbon bonds:
▪ Autotrophs – synthesize their own compounds
▪ Heterotrophs – absorbing organic compounds from environment
Chapter 30 – Protists
Eukarya –
• The third domain on the tree of life
• The largest and most morphologically complex organisms on the tree of life – algae, plants, fungi,
and animals – are eukaryotes
• Features that distinguish eukaryotes from bacteria and archaea
o Large, more organelles, more extensive system of structural proteins called the
cytoskeleton
o The nuclear envelope is a synapomorphy that defines the Eukarya
o Multicellularity is rare in bacteria and unknown if archaea, but has evolved multiple
times in eukaryotes
o Bacteria and archaea reproduce asexually by fission; many eukaryotes reproduce
asexually via mitosis and cell division
o Many eukaryotes undergo meiosis and reproduce sexually
Protists –
• Refer to a paraphyletic group, no synapomorphies define protists
o Have no traits that is found only in protists and in no other organisms
• Tend to live in environments where they are surrounded by water most of the time
• All eukaryotes are protists except the fungi, animals, and land plants
• Biologists study protists for three reasons:
o They are important medically
o They are important ecologically
o They are critical to understanding the evolution of plants, fungi, and animals
• Impacts on Human Health and Welfare
o The Irish potato famine was caused by a protist
▪ Phytophthora infestans
o Malaria is caused by a protist – apicomplexan species in the eukaryotic lineage Alveolata
o Five species of the protist Plasmodium are capable of parasitizing humans
• Harmful Algal Blooms
o Harmful algal blooms are usually due to photosynthetic protists called dinoflagellates
o Certain dinoflagellates synthesize toxins to protect themselves from predation by small
animals called copepods
Endosymbiosis and origin of the mitochondria
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Document Summary
Atp is produced by photophosphorylation: chemoorganotrophs oxidize organic molecules with high potential energy such as sugars. Atp may be produced by cellular respiration with sugars serving as electron donors or via fermentation pathways: chemolithotrophs oxidize inorganic molecules with high potential energy such as ammonia or methane. Atp is produced by cellular respiration and inorganic compounds serve as the electron donor: bacteria and archaea obtain building-block compounds with carbon-carbon bonds, autotrophs synthesize their own compounds, heterotrophs absorbing organic compounds from environment. Chapter 31 green algae and land plants. E. g. mosses: seedless vascular plants have vascular tissue but do not make seeds. Instead, they make spores that are carried by wind. E. g. ferns: seed plants have vascular tissue. A seed consists of an embryo and a store of nutritive tissue surrounded by a tough protective layer. Found in fossils and present day mosses: primary wall (with cellulose, first vascular tissue: some structural support.
