Chapter 19
The Origin of Life and the
Evolution of Cells
Biology 100
Early Ideas of Origin of Life
• Spontaneous generation was a concept proposed
by Aristotle around mid-300 B.C. which is the
hypothesis that living things arise from non-living
material
– Widely accepted theory for a long period of time
– Believed maggots arose from decaying meat, lice
formed from sweat, and frogs originating from mud
• An opposing theory was biogenesis is the concept
that life originates only from preexisting life
Disproving Spontaneous Generation
• In 1668, Francesco Redi, performed an experiment
where he set up two sets of jars with decaying meat,
one which was covered by gauze, the other one left
exposed
– Redi saw that the gauze blocked their access
• Flies arose from the open jar, so Redi concluded that
maggots arose from the eggs of flies
Disproving Spontaneous Generation
• In 1861, Louis Pasteur placed a fermented
sugar solution and yeast mixture in a flask
with a long swan neck and boiled. The flask
was left open, and for a control, one flask was
neck was broken off.
Endosymbiotic Theory
• Biologists generally believe that eukaryotes
evolved from prokaryotes
– Eukaryotes have their DNA in a nucleus and
membrane bound organelles
• The Endosymbiotic Theory states that present
day eukaryotic cells evolved from the uniting
of several types of primitive prokaryotic cells
– Some organelles (mitochondria and chloroplasts)
might have been were originally prokaryotes that
were involved in a symbiotic relationship
Endosymbiotic Theory
Chapter 20
The Classification and Evolution
of Organisms
Biology 100
Classification of Organisms
• Common names vary from culture to culture,
as well as varying between region to region
• Taxonomy is the science of naming organisms
and grouping them into local categories
• In 1758, Swedish doctor Carlos Linnaeus,
introduced the binomial system of
nomenclature uses two Latin names to
identify an organism
– Genus is a group of closely related organisms
– Species word added to the genus name to identify
which one of several species within the genus
Classification of Organisms
• So, the binomial system of nomunclature is in
the order Genus species
– In order to identify it as a scientific name, the
names are italicized in computer for of the genus
font, and underlined when hand-written
– The first letter of the genus is capitalized, while
species name is in lowercase
• Homo sapiens
Three Domains of Life
• There was a need for placing organisms into
groups.
• At first, there Linnaeus proposed plant and
animal kingdoms. Later on, the groups were
bacteria, plants and animals.
• The three major categories of organisms
called domains.
– Today, these three domains are Eubacteria,
Archaea, and Eucarya
Three Domains of Life
• Divided into these three domains are based on specific
structural and biochemical features of cells
– Prokaryotes
• Eubacteria
• Archaea
– Eukaryotes
• Eucarya
Classification
• In order to classify organisms, biologists see how a
species fits into different categories
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–
–
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–
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Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
• Mnemonics for classification: King Phyl Came Over For
Good Spaghetti, King Philip Came Over From Germany
Swimming
Classification of Humans
Taxonomic Category
Human
Characteristics
Classification
Other
Represenatives
Domain
Eucarya
Nucleus in cells, other kinds
of organelles
Plants, Animals,
Fungi, Protozoa,
Algae
Kingdom
Animalia
Eukaryotic heterotrophs
Sponges, jellyfish,
insects, cats
Phylum
Chordata
Animals with type of
backbone
Fish, reptiles,
mammals
Class
Mammalia
Animals with hair/mammary
gland
Kangaroos, mice,
whales, monkeys
Order
Primates
Mammals with large brain,
opposable thumbs
Monkeys, gorillas,
baboons
Family
Homindae
Primates lack tail and have
upright posture
Humans and extinct
relatives
Genus
Homo
Hominids with large brains
Humans only
surviving member
Species
Homo
sapiens
Humans
Eubacteria Domain
• Eubacteria, “true bacteria” are small,
prokaryotic, single-celled organisms
• Most Eubacteria are saprophytes, decomposing
dead organic matter for energy
• Some live in anaerobic environments (anoxic
mud, guts of herbivores), while others are
aerobic.
Archaea Domain
• The Archaea are the extremophiles, many living in some of the
least hospitable habitats on Earth.
• They have been discovered living in hot springs as hot as 140176oF in hot springs at Yellowstone National Park
• Others live as symbionts or free-living cells at deep seas
hydothermal vents at over 212oF.
• Some Archaea are decomposers in very anaerobic environments,
such as marshes
• Some live in the digestive systems of animals and produce
methane.
• Other species live in very salty environments like Great Salt Lake.
Eucarya Domain
• Eukaryotes are much larger than prokaryotes,
that allow them to have specialized
membranous organelles. There are several
different divisions (kingdoms) in the Domain
Eucarya.
– Kingdom Protista
– Kingdom Fungi
– Kingdom Plantae
– Kingdom Animalia
Kingdom Protista
• Traditionally, most single-celled eukaryotes
were lumped together in a group called the
Protista.
• The Protista also contains a few multicellular
colonial members.
• There are three major lines of evolution within
Protista.
– Plantlike autotrophs (Algae)
– Animal-like heterotrophs (Protozoa)
– Fungus-like heterotrophs (Slime molds)
Kingdom Fungi
• More commonly known as fungus and are
multicellular and non-motile.
• They form networks of multicellular filaments which
penetrate their environment.
• Most species are decomposers
• They secrete hydrolytic enzymes which digest dead
organic matters into smaller molecules which the
fungus absorbs.
• A few fungi are parasites, especially of plants,
sometimes animals.
Kingdom Plantae
• About 500 million years ago, a group of green
algae developed adaptations that enabled
them to invade the land. These are knownas
plants.
• Plants are nonmotile, terrestrial, and
multicellular organisms. They contain
chlorophyll and produce their own organic
compounds. All plant cells have a cellulose
cell wall.
Kingdom Animalia
• In this kingdom, all animals are motile,
heterotrophic, and multicellular.
Acellular Infectious Particles
• In order to be considered living, an organism
must have certain characteristics:
– Metabolism
– Reproduce independently
– Cellular organization
– Homeostasis
– Heredity
Acellular Infectious Particles
• Viruses are not considered “living” because
they do not meet the criteria of reproducing
independently
– Viruses are literally “parasitic” chemicals,
segments of DNA (or RNA) wrapped in a protein
coat
Structure of Viruses
• A virus is simply put, a protein with a core of
nucleic acid
– The protein sheath is known as a capsid which
surrounds their nucleic acid core
– In addition, some viruses form a membranelike
envelope, rich in proteins, lipids and glycoprotein
molecules around the capsid
Structure of Viruses
• Viruses vary in complexity and shape.
– Most animal and plant viruses are simpler in
appearance and are either helical or isometric
– Bacteriophages are generally more complex,
looking like a lunar lander
Bacteriaphages
• Bacteriophages are viruses that infect bacteria
– During the process of bacterial infection, one of
the tail fibers, contacts the lipoproteins of the
host bacterial cell wall.
– Then the contents of the head (DNA) are injected
into the host cytoplasm
– The virus infecting and killing the host cell is
known as the lytic cycle.
Lytic Cycle
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