Chapter 26 Early Earth and the Origin of Life
Life on Earth originated between 3.5 and 4.0 billion years ago
• The Earth formed about 4.5 billion years ago
• No clear fossils have been found in the oldest surviving Earth rocks, from 3.8 billion years
ago.
• The oldest fossils that have been uncovered were embedded in rocks from western
Australia that are 3.5 billion years ago.
Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years ago
• The earliest organisms were prokaryotes.
• Relatively early, prokaryotes diverged into two main evolutionary branches, the bacteria
and the archaea.
Oxygen began accumulating in the atmosphere about 2.7 billion years ago
• Photosynthesis probably evolved very early in prokaryotic history.
• Cyanobacteria, photosynthetic organisms that split water and produce O2 as a
byproduct, evolved over 2.7 billion years ago.
• This early oxygen initially reacted with dissolved iron to form the precipitate iron
oxide. This can be seen today in banded iron formations.
Eukaryotic life began by 2.1 billion years ago
• The first clear evidence of a eukaryote appeared about 2.1 billion years ago.
• This is the same time as the oxygen revolution that changed the Earth’s environment so
dramatically.
• Chloroplasts and mitochondrion evolved
Multicellular eukaryotes evolved by 1.2 billion years ago
• A great range of eukaryotic unicellular forms evolved into the diversity of present-day
“protists.”
Animal diversity exploded during the early Cambrian period
• Most of the major groups of animals make their first fossil appearances during the
relatively short span of the Cambrian period’s first 20 million years.
Plants, fungi, and animals colonized the land about 500 million years ago
• Most orders of modern mammals, including primates, appeared 50-60 million years ago.
• Humans diverged from other primates only 5 million years ago
The Origin of Life
• Spontaneous generation- life arises from nonliving matter
• In 1862, Louis Pasteur conducted broth experiments that rejected the idea of
spontaneous generation even for microbes.
• Biogenesis- all life today arises only by the reproduction of preexisting life.
One hypothesis is that chemical and physical processes in Earth’s primordial environment
eventually produced simple cells.
1) the abiotic synthesis of small organic molecules
2) joining these small molecules into polymers
3) origin of self-replicating molecule
4) packaging of these molecules into “protobionts”
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1. Abiotic synthesis of organic molecules
1920’s, A.I. Oparin and J.B.S. Haldane
 Conditions on the early Earth favored the synthesis of organic compounds from
inorganic precursors.
 The reducing environment in the early atmosphere would have promoted the joining of
simple molecules to form more complex ones.
 The energy required could be provided by lightning and the intense UV radiation that
penetrated the primitive atmosphere.
1953, Stanley Miller and Harold Urey
 The atmosphere model consisted of H2O, H2, CH4, and NH3.
 It produced a variety of amino acids and other organic molecules.
2. Laboratory simulations of early-Earth conditions have produced organic polymers
• Monomers should link to form polymers without enzymes and other cellular equipment.
• Researchers have produced polymers, including polypeptides, after dripping solutions of
monomers onto hot sand, clay, or rock.
3. RNA may have been the first genetic material
• Many researchers have proposed that the first hereditary material was RNA, not DNA.
• RNA can also function as an enzyme
• Short polymers of ribonucleotides can be synthesized abiotically in the laboratory.
• 1980’s Thomas Cech- discovered that RNA molecules are important catalysts in cells.
• Ribozymes- RNA catalysts that remove introns from RNA.
• Ribozymes also help catalyze the synthesis of new RNA polymers.
4A. Protobionts can form by self-assembly
• Protobionts- maintain an internal chemical environment from their surroundings and
may show some properties associated with life, metabolism, and excitability.
• Liposomes- droplets of abiotically produced organic compounds that form from lipids.
Forms a molecular bilayer like the lipid bilayer of a membrane.
• If enzymes are added, they are incorporated into the droplets.
• The protobionts are then able to absorb substrates from their surroundings and release
the products of the reactions catalyzed by the enzymes.
4B. Natural section could refine protobionts containing hereditary information
• Once primitive RNA genes and their polypeptide products were packaged within a
membrane, the protobionts could have evolved as units.
• The most successful protobionts would grow and split, distributing copies of their genes
to offspring. Later, DNA would replace RNA for storing genetic information.
Debates about the origin of life abounds
• Laboratory simulations cannot prove that these kinds of chemical processes actually
created life on the primitive Earth. They describe steps that could have happened.
• Among the debates is whether organic monomers on early Earth were synthesized in
deep-sea vents or reached Earth on comets and meteorites.
The five-kingdom system reflected increased knowledge of life’s diversity
• 1969, R.H Whittaker, A five-kingdom system: Monera, Protista, Plantae, Fungi, and Animalia.
Arranging the diversity of life into the highest taxa is a work in progress
• Three-domain system: Bacteria, Archaea, and Eukarya, as superkingdoms.
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Chapter 27 Prokaryotes and the Origins of Metabolic Diversity
They’re (almost) everywhere! An overview of prokaryotic life
• Prokaryotes were the earliest organisms on Earth and evolved alone for 1.5 billion years.
• Live in diverse environments.
• Most are benign or beneficial but others cause disease.
• Diverse in structure and in metabolism.
• About 5,000 species are known, but actual diversity may range from about 400,000 to 4
million species.
Bacteria and archaea are the two main branches of prokaryote evolution
The Structure, Function, and Reproduction of Prokaryotes
Most prokaryotes are unicellular.
The most common shapes among prokaryotes are spheres (cocci), rods (bacilli), and
helices.
Nearly all prokaryotes have a cell wall external to the plasma membrane
• Most bacterial cell walls contain peptidoglycan, a polymer of modified sugars crosslinked by short polypeptides.
Gram stain- used identify bacteria based on differences in their cell walls.
• Gram-positive bacteria have simpler cell walls, with large amounts of peptidoglycans.
• Gram-negative bacteria have more complex cell walls and less peptidoglycan.
• Generally more threatening. The outer membrane protects against host
defenses. More resistant to antibiotics.
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•
•
•
Many prokaryotes secrete a sticky protective layer, the capsule, outside the cell wall.
Pili- an appendage used to adhere to surfaces or other prokaryotes. Also used for
conjugation.
Many prokaryotes are motile
• Flagella
• Taxis- movement toward or away from a stimulus (chemicals, light, magnetic fields).
The cellular and genomic organization of prokaryotes is fundamentally different from that of
eukaryotes
• Prokaryotic cells lack a nucleus enclosed by membrane. They have smaller, simpler
genomes than eukaryotes and have small rings of DNA, plasmids, that consist of only a
few genes.
Populations of prokaryotes grow and adapt rapidly
• Prokaryotes reproduce only asexually via binary fission, synthesizing DNA almost
continuously.
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Transformation- a cell can absorb and integrate fragments of DNA from their
environment.
• Conjugation- one cell directly transfers genes to another cell.
• Transduction- viruses transfer genes between prokaryotes.
Endospore- forms when a cell replicates its chromosome and surrounds one chromosome with
a durable wall.
Can survive lack of nutrients and water, extreme heat or cold, and most poisons.
May be dormant for centuries or more.
When the environment becomes more hospitable, the endospore absorbs water and
resumes growth.
Nutrition and Metabolic Diversity
Prokaryotes can be grouped into four categories according to how they obtain energy and
carbon
• Species that use light energy are phototrophs.
• Species that obtain energy from chemicals in their environment are chemotrophs.
• Organisms that need only CO2 as a carbon source are autotrophs.
• Organisms that require at least one organic nutrient as a carbon source are
heterotrophs.
• Photoautotrophs- photosynthetic organisms that harness light energy to drive the
synthesis of organic compounds from carbon dioxide.
• Ex: cyanobacteria.
• Chemoautotrophs need only CO2 as a carbon source, but they obtain energy by
oxidizing inorganic substances, rather than light.
• These substances include hydrogen sulfide (H2S), ammonia (NH3), and ferrous
ions (Fe2+) among others.
• Photoheterotrophs use light to generate ATP but obtain their carbon in organic form.
• Chemoheterotrophs must consume organic molecules for both energy and carbon.
Prokaryotes are responsible for the key steps in the cycling of nitrogen through ecosystems.
• Some convert ammonium (NH4+) to nitrite (NO2-).
• Others convert nitrite or nitrate (NO3-) to N2 (gas).
• Nitrogen fixation- convert N2 to NH4+, making atmospheric nitrogen available to other
organisms for incorporation into organic molecules.
Obligate aerobes- require O2 for cellular respiration.
Facultative anerobes- will use O2 if present but can also grow by fermentation in an anaerobic
environment.
Obligate anaerobes- are poisoned by O2 and use either fermentation or anaerobic respiration.
Photosynthesis evolved early in prokaryotic life
• The very first prokaryotes were heterotrophs, but photosynthesis capabilities soon
followed.
A Survey of Prokaryotic Diversity
Molecular systematics is leading to phylogenetic classification of prokaryotes
• Carl Woese clustered prokarotes into taxonomic groups based on comparisons of
nucleic acid sequences- small-subunit ribosomal RNA (SSU-rRNA)
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Researchers are identifying a great diversity of archaea in extreme environments and in the
oceans
• Archaea are extremophiles, “lovers” of extreme environments.
Methanogens obtain energy by using CO2 to oxidize H2 replacing methane as a waste.
• They live in swamps and marshes where other microbes have consumed all the oxygen.
• Methanogens are important decomposers in sewage treatment.
• Other methanogens live in the anaerobic guts of herbivorous animals, playing an
important role in their nutrition.
Extreme halophiles live in such saline places as the Great Salt Lake and the Dead Sea.
Extreme thermophiles thrive in hot environments, 60oC-80oC, hot sulfur springs or at 105oC
water near deep-sea hydrothermal vents
Most known prokarotes are bacteria
Proteobacteria, Chlamydias, Spirochetes, Gram-Positive Bacteria, Cyanobacteria
The Ecological Impact of Prokaryotes
Prokaryotes are indispensable links in the recycling of chemical elements in ecosystems
• Decomposers
• Metabolize inorganic molecules containing elements such as iron, sulfur, nitrogen, and
hydrogen
• Restore oxygen to the atmosphere
• Fix nitrogen
Many prokaryotes are symbiotic
• Commensalism, one symbiont receives benefits while the other is not harmed or helped
by the relationship.
• Parasitism, one symbiont, the parasite, benefits at the expense of the host.
• Mutualism, both symbionts benefit.
Pathogenic prokaryotes cause many human diseases
• Some pathogens are opportunistic. These are normal residents of the host, but only
cause illness when the host’s defenses are weakened.
Exotoxins are proteins secreted by prokaryotes.
C. botulinum, V. cholerae, E. coli
Endotoxins are components of the outer membranes of some gram-negative bacteria.
Salmonella
Humans use prokaryotes in research and technology
• The application of organisms to remove pollutants from air, water, and soil is
bioremediation.
• Decomposers treat human sewage.
• Soil bacteria have been developed to decompose petroleum products at the site of oil
spills or to decompose pesticides.
• The chemical industry produces acetone, butanol, and other products from bacteria.
• The pharmaceutical industry cultures bacteria to produce vitamins and antibiotics.
• The food industry used bacteria to convert milk to yogurt and various kinds of cheese.
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Chapter 28 The Origins of Eukaryotic Diversity
Introduction to the Protists
The first eukaryotes were unicellular.
Eukaryotic fossils date back 2.1 billion years
For about 2 billion years, eukaryotes consisted of mostly microscopic organisms“protists.”
Systematists have split protists into many kingdoms
• Systematists have split the former kingdom Protista into as many as 20 separate
kingdoms.
Protists are the most diverse of all eukaryotes
• Most of the 60,000 known protists are unicellular, but some are colonial and others
multicellular.
• Protists are the most nutritionally diverse of all eukaryotes.
• Aerobic w/ mitochondria, photoautotrophs w/ chloroplasts, heterotrophs,
mixotrophs- combining photosynthesis and heterotrophic nutrition.
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•
•
•
Euglena, mixotrophic, can use chloroplasts to undergo photosynthesis if light is available or live as a
heterotroph by absorbing organic nutrients from the environment.
The Origin and Early Diversification of Eukaryotes
Unique cellular structures and processes:
• Membrane-enclosed nucleus, Endomembrane system, Mitochondria,
Chloroplasts, Cytoskeleton, 9 + 2 flagella, Multiple chromosomes of linear DNA
with organizing proteins, Life cycles with mitosis, meiosis, and sex.
Endomembranes contributed to larger, more complex cells
• The endomembrane system of eukaryotes (nuclear envelope, endoplasmic reticulum,
Golgi apparatus, and related structures) may have evolved from infoldings of plasma
membrane.
Mitochondria and plastids evolved from endosymbiotic bacteria
• The theory of serial endosymbiosis proposes that mitochondria and chloroplasts were
formerly small prokaryotes living within larger cells.
• These ancestors probably entered the host cells as undigested prey or internal parasites.
• This evolved into a mutually beneficial symbiosis.
The eukaryotic cell is a chimera of prokaryotic ancestors
• mitochondria from one bacteria
• plastids from another
• nuclear genome from the host cell
Secondary endosymbiosis increased the diversity of algae
• The chloroplasts of plants and green algae have two membranes.
• The plastids of others have three or four membranes.
• These include the plastids of Euglena (with three membranes) that are
most closely related to heterotrophic species.
• Those algal groups with more than two membranes were acquired by
secondary endosymbiosis.
•
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•
Each endosymbiotic event adds a membrane derived from the vacuole
membrane of the host cell that engulfed the endosymbiont.
Research on the relationships between the three domains is changing ideas about the
deepest branching in the tree of life
• All three domains seem to have genomes that are chimeric mixes of DNA that was
transferred across the boundaries of the domains.
• In this new model, the three domains arose from an ancestral community of primitive
cells that swapped DNA promiscuously.
The origin of eukaryotes catalyzed a second great wave of diversification
• The development of clades among the diverse groups of eukaryotes is based on
comparisons of cell structure, life cycles, and molecules.
A Sample of Protistan Diversity
Diplomonadida and Parabasala
The diplomonads have multiple flagella, two separate nuclei, a simple cytoskeleton, and no
mitochondria or plastids.
• Giardia lamblia, a parasite that infects the human intestine.
The parabasalids include trichomonads.
• Trichomonas vaginalis, inhabits the vagina of human females.
Euglenozoa
The euglenozoa includes both photosynthetic and heterotrophic flagellates
• The euglenoids (Euglenozoa) are characterized by an anterior pocket from which one or
two flagella emerge.
• The kinetoplastids (Kinoplastida) have a single large mitochondrion associated with a
unique organelle, the kinetoplast.
• The kinetoplast houses extranuclear DNA.
• Trypanosoma causes African sleeping sickness.
Alveolata
The alveolata are unicellular protists with subcellular cavities (alveoli)
• Flagellated protists (dinoflagellates), parasites (apicomplexans), and ciliated protists (the
ciliates).
• Alveoli- small membrane-bound cavities, under the cell surface.
•
•
Their function is not known, but they may help stabilize the cell surface and regulate water and
ion content.
Dinoflagellates are abundant components of the phytoplankton that are suspended
near the water surface.
• Dinoflagellates and other phytoplankton form the foundation of most marine
and many freshwater food chains.
• Dinoflagellate blooms, characterized by explosive population growth, cause red
tides in coastal waters.
• Pfiesteria piscicida, is carnivorous. This organism produces a toxin that stuns fish.
• Some dinoflagellates are bioluminescent.
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Apicomplexans are parasites of animals and some cause serious human diseases.
• Tiny infectious cells (sporozoites) penetrate host cells and tissues.
• Intricate life cycles with both sexual and asexual stages and often require two or
more different host species for completion.
• Plasmodium, the parasite that causes malaria, spends part of its life in
mosquitoes and part in humans.
• Ciliophora (ciliates), a diverse protist group, is named for their use of cilia to move and
feed.
• Paramecium, cilia along the oral groove draw in food that is engulfed by
phagocytosis.
• Ciliates have two types of nuclei, a large macronucleus and usually several tiny
micronuclei.
• Conjugation- micronuclei are exchanged.
Stramenopila
Heterotrophic and photosynthetic protists.
Numerous fine, hairlike projections on the flagella.
In most stramenopile groups, the only flagellated stage is motile reproductive cells.
The heterotrophic stramenopiles, the oomycotes, include water molds, white rusts, and
downy mildews.
Water molds are important decomposers, mainly in fresh water.
White rusts and downy mildews are parasites of terrestrial plants.
The photosynthetic stramenopiles are known collectively as the heterokont algae.
• The heterokont algae include diatoms, golden algae, and brown algae.
• Diatoms (Bacillariophyta) have unique glasslike walls composed of hydrated silica
embedded in an organic matrix.
• Golden algae (Chrysophyta), named for the yellow and brown carotene and
xanthophyll pigments, are typically biflagellated.
• Brown algae (Phaeophyta) are the largest and most complex algae. Most brown
algae are multicellular.
Structural and biochemical adaptations help seaweeds survive and reproduce at the ocean’s
margins
• Brown, red, and green algae inhabit the intertidal and subtidal zones of coastal waters.
• Thallus or body of the seaweed: rootlike holdfast and a stemlike stipe, which supports
leaflike photosynthetic blades.
• Giant brown algae, known as kelps, form forests in deeper water.
• The stipes of these plants may be 60 m long.
Some algae have life cycles with alternating multicellular haploid and diploid generations
• The diploid individual, the sporophyte, produces haploid spores (zoospores) by meiosis.
• The haploid individual, the gametophyte, produces gametes by mitosis that fuse to form
a diploid zygote.
Rhodophyta: Red algae lack flagella
• Red algae have no flagellated stages in their life cycle.
• In the absence of flagella, fertilization depends entirely on water currents to
bring gametes together.
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Chlorophyta
Green algae and plants evolved from a common photoautotrophic ancestor
• Green algae (chlorophytes and charophyceans) are named for their grass-green
chloroplasts.
• Most of the 7,000 species of chlorophytes live in freshwater.
• Most green algae have both sexual and asexual reproductive stages.
A diversity of protists use pseudopodia for movement and feeding
• Three groups of protists use pseudopodia, cellular extensions, to move and often to
feed.
• Rhizopods (amoebas) are all unicellular and use pseudopodia to move and to feed.
• Actinopod (heliozoans and radiolarians), “ray foot,” refers to slender pseudopodia
(axopodia) that radiate from the body.
• Each axopodium is reinforced by a bundle of microtubules covered by a thin
layer of cytoplasm.
• Foraminiferans, or forams, are almost all marine.
Mycetozoa
Slime molds have structural adaptations and life cycles that enhance their ecological roles as
decomposers.
• The feeding stage is an amoeboid mass, the plasmodium, that may be several
centimeters in diameter.
• The cellular slime molds (Dictyostelida)
• The feeding stage consists of solitary cells. When food is scarce, the cells form an
aggregate (“slug”) that functions as a unit.
Multicellularity originated independently many times
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Chapter 28 The Origins of Eukaryotic Diversity continued
Chlorophyta
Green algae and plants evolved from a common photoautotrophic ancestor
• Green algae (chlorophytes and charophyceans) are named for their grass-green
chloroplasts.
• Most of the 7,000 species of chlorophytes live in freshwater.
• Most green algae have both sexual and asexual reproductive stages.
A diversity of protists use pseudopodia for movement and feeding
• Three groups of protists use pseudopodia, cellular extensions, to move and often to
feed.
• Rhizopods (amoebas) are all unicellular and use pseudopodia to move and to feed.
• Actinopod (heliozoans and radiolarians), “ray foot,” refers to slender pseudopodia
(axopodia) that radiate from the body.
• Each axopodium is reinforced by a bundle of microtubules covered by a thin
layer of cytoplasm.
• Foraminiferans, or forams, are almost all marine.
Mycetozoa
Slime molds have structural adaptations and life cycles that enhance their ecological roles as
decomposers.
• The feeding stage is an amoeboid mass, the plasmodium, that may be several
centimeters in diameter.
• The cellular slime molds (Dictyostelida)
• The feeding stage consists of solitary cells. When food is scarce, the cells form an
aggregate (“slug”) that functions as a unit.
Multicellularity originated independently many times
Chapter 29-30 Plant Diversity
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An Overview of Land Plant Evolution
• More than 280,000 species of plants inhabit Earth today.
• Land plants evolved from a green algae, called charophyceans.
Evolutionary adaptations to terrestrial living characterize the four main groups of land plants
• There are four main groups of land plants: bryophytes, pteridophytes, gymnosperms, and
angiosperms.
• Four great episodes in the evolution of land plants:
• the origin of bryophytes from algal ancestors
• the origin and diversification of vascular plants
• the origin of seeds
• the evolution of flowers
Charophyceans are the green algae most closely related to land plants
• The plasma membranes have a particular cellulose structure of the cell wall.
• The presence of peroxisomes.
• Enzymes in peroxisomes help minimize the loss of organic products due to
photorespiration.
• Land plants that have flagellated sperm cells which are similar to charophyceans.
Several terrestrial adaptations distinguish land plants from charophycean algae
• Apical meristems
• localized regions of cell division at the tips of shoots and roots
• Multicellular embryos dependent on the parent plant
• Alternation of generations
• Gametophyte- haploid cells, produces: gametes (egg and sperm.)
• Sporophyte- diploid cells, produces: haploid spores.
• A spore is a reproductive cell that can develop into a new
organism without fusing with another cell.
• Sporangia that produce walled spores
• Sporangia- are found on the sporophyte and haploid produce spores by
meiosis.
• Spores are covered by a polymer called sporopollenin, the most durable
organic material known.
•
Gametangia that produce gametes
• Archegonium- a female gametangium, produces a single egg cell in a
vase-shaped organ.
• Antheridia- a male gametangia, produces many sperm cells that are
released to the environment.
Cuticle- covers leaves with polyesters and waxes. Protects the plant from microbial attack.
Waterproofing to prevent excessive water loss.
Stomata- pores in the epidermis of leaves allow the exchange of carbon dioxide and oxygen
between the outside air and the leaf interior.
Xylem- Tube-shaped cells carry water and minerals up from roots. Cells are dead.
Phloem- is a living tissue in which nutrient-conducting cells arranged into tubes distribute
sugars, amino acids, and other organic products.
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Land plants evolved from charophycean algae over 500 million years ago
• The oldest known traces of land plants are found in mid-Cambrian rocks from about 550
million years ago.
Alternation of generations in plants may have originated by delayed meiosis
Adaptations to shallow water preadapted plants for living on land
Plant taxonomists are reevaluating the boundaries of the plant kingdom
Bryophytes
The three phyla of bryophytes are mosses, liverworts, and hornworts
• phylum Hepatophyta - liverworts
• phylum Anthocerophyta - hornworts
• phylum Bryophyta - mosses
The gametophyte is the dominant generation in the life cycles of bryophytes
• Sporophytes are smaller and present only part of the time.
Gametophores-generate gametes
• Bryophytes are anchored by tubular cells or filaments of cells, called rhizoids.
• not composed of tissues, lack specialized conducting cells, do not play a primary
role in water and mineral absorption.
Bryophyte sporophytes disperse enormous numbers of spores
Bryophytes provide many ecological and economic benefits
• Wet regions dominated by Sphagnum or peat moss are known as peat bogs.
• Carbon reservoirs- stabilizes atmospheric carbon dioxide levels.
• Used in the past as diapers and a natural antiseptic material for wounds.
The Origin of Vascular Plants
A diversity of vascular plants evolved over 400 million years ago
• Cooksonia, an extinct plant over 400 million years old, is the earliest known vascular
plant.
Pteridophytes: Seedless Vascular Plants
• phylum Lycophyta - lycophytes
• phylum Pterophyta - ferns, whisk ferns, and horsetails
A sporophyte-dominant life cycle evolved in seedless vascular plants
• The leafy fern plants are sporophytes.
• The gametophytes are tiny plants that grow on or just below the soil surface.
A homosporous sporophyte produces a single type of spore.
• A heterosporous sporophyte produces two kinds of spores.
• Megaspores develop into females gametophytes.
• Microspores develop into male gametophytes.
Lycophyta and Pterophyta are the two phyla of modern seedless vascular plants
• Phylum Lycophyta - Modern lycophytes are relicts of a far more eminent past.
• Phylum Pterophyta: Psilophytes, the whisk ferns
• Sphenophytes are commonly called horsetails because of their often brushy
appearance.
• Ferns first appeared in the Devonian and have radiated extensively until there
are over 12,000 species today.
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Ferns produce clusters of sporangia, called sori, on the back of green leaves
(sporophylls) or on special, non-green leaves.
Overview of Seed Plant Evolution
(1) the evolution of seeds, which lead to the gymnosperms and angiosperms, the plants that
dominate most modern landscapes
(2) the emergence of the importance of seed plants to animals, specifically to humans.
Agriculture, the cultivation and harvest of plants (primarily seed plants), began approximately
10,000 years ago in Asia, Europe, and the Americas.
Seed plants are vascular plants that produce seeds.
• Important reproductive adaptations:
• 1. Continued reduction of the gametophyte
• 2. The advent of the seed
• 3. The evolution of pollen.
1. Reduction of the gametophyte continued with the evolution of seed plants
• The gametophytes of seed plants are even more reduced than those of seedless
vascular plants.
2. Seeds became an important means of dispersing offspring
• All seed plants are heterosporous, producing two different types of sporangia that
produce two types of spores (megaspores and microspores).
• Layers of sporophyte tissues, integuments, envelop and protect the megasporangium.
• An ovule consists of integuments, megaspore, and megasporangium.
3. Pollen eliminated the liquid-water requirement for fertilization
• They are carried away by wind or animals until pollination occurs when they land in the
vicinity of an ovule.
Gymnosperms
The four phyla of gymnosperms are ginko, cycads, gnetophytes, and conifers
• Phylum Ginkgophyta consists of only a single extant species, Ginkgo biloba.
• Ornamental species has fanlike leaves that turn gold before they fall off in the
autumn.
• Landscapers usually only plant male trees because the seed coats on female
plants decay, they produce a repulsive odor.
• Cycads (phylum Cycadophyta) superficially resemble palms.
• Palms are actually flowering plants.
• Phylum Gnetophyta consists of three very different genera.
• Weltwitschia plants, from deserts in southwestern Africa, have straplike leaves.
• Gentum species are tropical trees or vines.
• Ephedra (Mormon tea) is a shrub of the American deserts.
The life cycle of a pine demonstrates the key reproductive adaptations of seed plants
• increasing dominance of the sporophyte
• seeds as a resistant, dispersal stage
• pollen as an airborne agent bringing gametes together.
• Conifers, are heterosporous, developing male and female gametophytes from different
types of spores produced by separate cones.
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Small pollen cones produce microspores that develop into male gametophytes,
or pollen grains.
• Larger ovulate cones make megaspores that develop into female gametophytes.
The conifers, phylum Coniferophyta, is the largest gymnosperm phylum. Conifers include
pines, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods.
• Much of our lumber and paper comes from the wood (actually xylem tissue) of conifers.
• Coniferous trees are amongst the largest and oldest organisms of Earth.
Angiosperms (Flowering Plants)
There are abut 250,000 known species of angiosperms.
All angiosperms are placed in a single phylum, the phylum Anthophyta.
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•
•
•
As late as the 1990s, most plant taxonomists divided the angiosperms into two main classes, the monocots and the
dicots.
Recent systematic analyses have upheld the monocots as a monophyletic group.
However, molecular systematics has indicated that plants with the dicot anatomy do not form a monophyletic group.
One clade, the eudicots, does include the majority of dicots.
The flower is the defining reproductive adaptation of angiosperms
• The flower is an angiosperm structure specialized for reproduction.
• A flower is a specialized shoot with four circles of modified leaves: sepals, petals,
stamens, and carpals.
• The sepals at the base of the flower are modified leaves that enclose the flower before
it opens.
• The petals lie inside the ring of sepals.
• Stamens, the male reproductive organs, are the sporophylls that produce microspores
that will give rise to gametophytes.
• A stamen consists of a stalk (the filament) and a terminal sac (the anther) where
pollen is produced.
• Carpals are female sporophylls that produce megaspores and their products, female
gametophytes.
• At the tip of the carpal is a sticky stigma that receives pollen. A style leads to the
ovary at the base of the carpal. Ovules and, later, seeds are protected within the
ovary.
Fruits help disperse the seeds of angiosperms
• A fruit is a mature ovary.
• As seeds develop from ovules after fertilization, the wall of the ovary thickens to
form the fruit.
• Fruits protect dormant seeds and aid in their dispersal.
• Simple fruits are derived from a single ovary.
• These may be fleshy, such as a cherry, or dry, such as a soybean pod.
• An aggregate fruit, such as a blackberry, results from a single flower with several
carpals.
• A multiple fruit, such as a pineapple, develops from an inflorescence, a tightly
clustered group of flowers.
The life cycle of an angiosperm is a highly refined version of the alternation of generations
common in plants
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All angiosperms are heterosporous, producing microspores that form male
gametophytes and megaspores that form female gametophytes.
• The immature male gametophytes are contained within pollen grains and
develop within the anthers of stamens.
• Each pollen grain has two haploid cells.
• Ovules, which develop in the ovary, contain the female gametophyte, the
embryo sac.
• It consists of only a few cells, one of which is the egg.
Angiosperms and animals have shaped one another’s evolution
• Ever since they colonized the land, animals have influenced the evolution of terrestrial
plants and vice versa.
• This type of mutual evolutionary influence between two species is termed coevolution.
Plants and Human Welfare
Agriculture is based almost entirely on angiosperms
Plant diversity is a nonrenewable resource
• Almost all of our food is based on cultivation of only about two dozen species.
• More than 25% of prescription drugs are extracted from plants, and many more
medicinal compounds were first discovered in plants and then synthesized artificially.
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Chapter 31 Fungi
Fungi are heterotrophs that feed by absorption
Nutrition and Ecology
– Fungi use enzymes to break down a large variety of complex molecules into
smaller organic compounds
Fungi exhibit diverse lifestyles:
– Decomposers
– Parasites
– Mutualists
The most common body structures are multicellular filaments and single cells (yeasts)
Fungi consist of mycelia, networks of branched hyphae adapted for absorption
Most fungi have cell walls made of chitin
Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement
of organelles
Coenocytic fungi lack septa
Some unique fungi have specialized hyphae called haustoria that allow them to penetrate the
tissues of their host
Mycorrhizae are mutually beneficial relationships between fungi and plant roots
Fungi produce spores through sexual or asexual life cycles
• Fungi propagate themselves by producing vast numbers of spores, either sexually or
asexually
• Fungi can produce spores from different types of life cycles
Sexual Reproduction
• Plasmogamy is the union of two parent mycelia
• In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist
in the mycelium, called a heterokaryon
• In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be
dikaryotic
• During karyogamy, nuclear fusion, the haploid nuclei fuse, producing diploid cells
• The diploid phase is short-lived and undergoes meiosis, producing haploid spores
Asexual Reproduction
• In addition to sexual reproduction, many fungi can reproduce asexually
• Molds produce haploid spores by mitosis and form visible mycelia
• Other fungi that can reproduce asexually are yeasts, which inhabit moist environments
• Instead of producing spores, yeasts reproduce asexually by simple cell division and the
pinching of “bud cells” from a parent cell
No sexual Reproduction
• Many molds and yeasts have no known sexual stage
• Mycologists have traditionally called these deuteromycetes, or imperfect fungi
The ancestor of fungi was an aquatic, single-celled, flagellated protist
• Fungi and animals are more closely related to each other than they are to plants or
other eukaryotes
• The oldest undisputed fossils of fungi are only about 460 million years old
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Chytrids
• Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats
• They can be decomposers, parasites, or mutualists
• Molecular evidence supports the hypothesis that chytrids diverged early in fungal
evolution
• Chytrids are unique among fungi in having flagellated spores, called zoospores
Zygomycetes
• The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories
• They include fast-growing molds, parasites, and commensal symbionts
• The zygomycetes are named for their sexually produced zygosporangia
• Zygosporangia, which are resistant to freezing and drying, can survive unfavorable
conditions
Glomeromycetes
• Glomeromycetes (phylum Glomeromycota)
• Glomeromycetes have mycorrhizae (mutually beneficial relationships between fungi
and plant roots)
Ascomycetes
• Ascomycetes (phylum Ascomycota) live in marine, freshwater, and terrestrial habitats
• The phylum is defined by production of sexual spores in saclike asci, usually contained in
fruiting bodies called ascocarps
• Commonly called sac fungi
• Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels
• Reproduce asexually by enormous numbers of asexual spores called conidia
• Conidia are not formed inside sporangia; they are produced asexually at the tips of
specialized hyphae called conidiophores
Basidiomycetes
• Basidomycetes (phylum Basidiomycota) include mushrooms, puffballs, and shelf fungi,
mutualists, and plant parasites
• The phylum is defined by a clublike structure called a basidium, a transient diploid stage
in the life cycle
• The basidiomycetes are also called club fungi
• The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium
• In response to environmental stimuli, the mycelium reproduces sexually by producing
elaborate fruiting bodies call basidiocarps
• Mushrooms are examples of basidiocarps
• The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores
Fungi play key roles in nutrient cycling, ecological interactions, and human welfare
Fungi are efficient decomposers
Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals
Mycorrhizae are enormously important in natural ecosystems and agriculture
Some fungi share their digestive services with animals. They help break down plant material in
the guts of cows and other grazing mammals.
Many species of ants and termites use the digestive power of fungi by raising them in “farms”
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Lichens
• A lichen is a symbiotic association between a photosynthetic microorganism and a
fungus in which millions of photosynthetic cells are held in a mass of fungal hyphae
• The fungal component of a lichen is most often an ascomycete
• Algae or cyanobacteria occupy an inner layer below the lichen surface
• The algae provide carbon compounds, cyanobacteria provide organic nitrogen, and
fungi provide the environment for growth
• Lichens are important pioneers on new rock and soil surfaces
• Lichens are sensitive to pollution, and their death can be a warning that air quality is
deteriorating
Fungi as Pathogens
• About 30% of known fungal species are parasites or pathogens, mostly on or in plants
• Some fungi that attack food crops are toxic to humans
• Animals are much less susceptible to parasitic fungi than are plants
• The general term for a fungal infection in animals is mycosis
Practical Uses of Fungi
• Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread
• Some fungi are used to produce antibiotics for the treatment of bacterial infections, for
example the ascomycete Penicillium
• Genetic research on fungi is leading to applications in biotechnology
– For example, insulin-like growth factor can be produced in the fungus
Saccharomyces cerevisiae
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Chapter 32 Introduction to Animal Evolution
1.3 million living species of animals have been identified
Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic
layers
Animals are heterotrophs that ingest their food
Animals are multicellular eukaryotes
Their cells lack cell walls
Their bodies are held together by structural proteins such as collagen
Nervous tissue and muscle tissue are unique to animals
Reproduction and Development
• Most animals reproduce sexually, with the diploid stage usually dominating the life cycle
• After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage
• Cleavage leads to formation of a blastula
• The blastula undergoes gastrulation, forming a gastrula with different layers of
embryonic tissues
• Many animals have at least one larval stage
• A larva is sexually immature and morphologically distinct from the adult; it eventually
undergoes metamorphosis
The history of animals spans more than half a billion years
• The common ancestor of living animals may have lived between 675 and 875 million
years ago
• Early members of the animal fossil record include the Ediacaran biota, which dates from
565 to 550 million years ago
Paleozoic Era (542–251 Million Years Ago)
• The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil
appearance of many major groups of living animals
• There are several hypotheses regarding the cause of the Cambrian explosion
– New predator-prey relationships
– A rise in atmospheric oxygen
– The evolution of the Hox gene complex
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Animals can be characterized by “body plans”
• Radial symmetry
• Bilateral symmetry
– A dorsal (top) side and a ventral (bottom) side
– A right and left side
– Anterior (head) and posterior (tail) ends
– Cephalization, the development of a head
Tissues
• Ectoderm is the germ layer covering the embryo’s surface
• Endoderm is the innermost germ layer and lines the developing digestive tube, called
the archenteron
• Diploblastic animals have ectoderm and endoderm
• Triploblastic animals also have an intervening mesoderm layer; these include all
bilaterians
Body Cavities
• Most triploblastic animals possess a body cavity
• A true body cavity is called a coelom and is derived from mesoderm
• Coelomates are animals that possess a true coelom
• A pseudocoelom is a body cavity derived from the mesoderm and endoderm
• Triploblastic animals that possess a pseudocoelom are called pseudocoelomates
• Triploblastic animals that lack a body cavity are called acoelomates
Protostome and Deuterostome Development (see picture below)
Some lophotrochozoans have a feeding structure called a lophophore
Other phyla go through a distinct developmental stage called the trochophore larva
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Chapter 33 Invertebrates
Overview: Life Without a Backbone
• Invertebrates are animals that lack a backbone
• They account for 95% of known animal species
Calcarea and Silicea
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Sponges are basal animals that lack true tissues
Sedentary animals
Live in both fresh and marine waters
Lack true tissues and organs
Suspension feeders, capturing food particles suspended in the water that pass through their body
Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended
food
Water is drawn through pores into a cavity called the spongocoel, and out through an opening called the
osculum
Sponges consist of a noncellular mesohyl layer between two cell layers
Amoebocytes are found in the mesohyl and play roles in digestion and structure
Most sponges are hermaphrodites: Each individual functions as both male and female
Cnidarians
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All animals except sponges and a few other groups belong to the clade Eumetazoa, animals with true
tissues
Sessile and motile forms including jellies, corals, and hydras
Simple diploblastic, radial body plan
The basic body plan is a sac with a central digestive compartment, the gastrovascular cavity
A single opening functions as mouth and anus
Sessile polyp and motile medusa
Carnivores that use tentacles to capture prey
The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey
Nematocysts are specialized organelles within cnidocytes that eject a stinging thread
Lophotrochozoans
• A clade with the widest range of animal body forms
• Some develop a lophophore for feeding, others pass through a trochophore larval stage,
and a few have neither feature
Platyhelminthes (Flatworms)
• Live in marine, freshwater, and damp terrestrial habitats
• Triploblastic development, but are acoelomates
• They are flattened dorsoventrally and have a gastrovascular cavity
• Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance
Planarians
• Light-sensitive eyespots and centralized nerve nets
• Hermaphrodites and can reproduce sexually, or asexually through fission
Trematodes
 Parasitize humans spend part of their lives in snail hosts
Tapeworms
 parasites of vertebrates and lack a digestive system
 Absorb nutrients from the host’s intestine
 Fertilized eggs, produced by sexual reproduction, leave the host’s body in feces
Rotifera
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Rotifers are tiny animals that inhabit fresh water, the ocean, and damp soil
Multicellular and have specialized organ systems
Reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs
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Lophophorates: Ectoprocts and Brachiopods
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Lophophorates have a lophophore, a horseshoe-shaped, suspension-feeding organ with ciliated tentacles
Ectoprocts- colonial animals that superficially resemble plants
A hard exoskeleton encases the colony, and some species are reef builders
Brachiopods resemble clams but the two halves of the shell are dorsal and ventral rather than lateral as in
clams
Mollusca
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Snails and slugs, oysters and clams, and octopuses and squids
Most are marine, though some inhabit fresh water and some are terrestrial
Soft-bodied animals, but most are protected by a hard shell
• Three main parts: Muscular foot, Visceral mass, Mantle
Many also have a water-filled mantle cavity, and feed using a rasplike radula
The most distinctive characteristic of gastropods is torsion, which causes the animal’s anus and mantle to
end up above its head
Cephalopods have a closed circulatory system, well-developed sense organs, and a complex brain
Annelids
• Bodies composed of a series of fused rings
Earthworms
• Eat through soil, extracting nutrients as the soil moves through the alimentary canal
• Hermaphrodites but cross-fertilize
Polychaetes
 Have paddle-like parapodia that work as gills and aid in locomotion
Leeches
• Blood-sucking parasites, secrete a chemical called hirudin to prevent blood from coagulating
Ecdysozoans
Clade of Ecdysozoans- covered by a tough coat called a cuticle. The cuticle is shed or
molted through a process called ecdysis
• The two largest phyla are nematodes and arthropods
Nematodes (roundworms)
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Nematodes, or roundworms, are found in most aquatic habitats, in the soil, in moist tissues of plants, and
in body fluids and tissues of animals
They have an alimentary canal, but lack a circulatory system
Reproduction in nematodes is usually sexual, by internal fertilization
Some species are parasites of plants and animals
Arthropods
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Two out of every three known species of animals are arthropods
The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages, and
dates to the Cambrian explosion (535–525 million years ago)
• Arthropod evolution is characterized by a decrease in the number of segments and an increase in
appendage specialization
• These changes may have been caused by changes in Hox gene sequence or regulation
• The appendages of some living arthropods are modified for many different functions
• The body is completely covered by the cuticle, an exoskeleton made of layers of protein and the
polysaccharide chitin
• When an arthropod grows, it molts its exoskeleton
• Open circulatory system- fluid is circulated into the spaces surrounding the tissues and organs
• A variety of organs specialized for gas exchange have evolved in arthropods
Cheliceriforms Most marine ones are extinct, but some species survive today, including horseshoe crabs
Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites
• Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages, the most anterior of
which are the chelicerae
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Insects
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Gas exchange in spiders occurs in respiratory organs called book lungs
Subphylum Myriapoda includes millipedes and centipedes
Centipedes, class Chilopoda, are carnivores, one pair of legs per trunk segment
Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined
Flight is one key to the great success of insects
Incomplete metamorphosis- the young, called nymphs, resemble adults but are smaller and go through a
series of molts until they reach full size
Complete metamorphosis- have larval stages known by such names as maggot, grub, or caterpillar. The
larval stage looks entirely different from the adult stage
Most insects have separate males and females and reproduce sexually
Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops
Insects are classified into more than 30 orders
Crustaceans
• Isopods- terrestrial, freshwater, and marine species, ex: Pill bugs
• Decapods- relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp
• Planktonic crustaceans include many species of copepods, which are among the most numerous of all
animals
Deuterostomes
Shared characteristics define deuterostomes (Chordates and Echinoderms)
– Radial cleavage
– Formation of the mouth at the end of the embryo opposite the blastopore
Echinoderms
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Sea stars and most other echinoderms are slow-moving or sessile marine animals
A thin epidermis covers an endoskeleton of hard calcareous plates
Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube
feet that function in locomotion, feeding, and gas exchange
• Males and females are usually separate, and sexual reproduction is external
Sea Stars
• Multiple arms radiating from a central disk
• The undersurfaces of the arms bear tube feet, each of which can act like a suction disk
• Can regrow lost arms
Brittle Stars
 Distinct central disk and long, flexible arms, which they use for movement
Sea Urchins and Sand Dollars
 Sea urchins and sand dollars have no arms but have five rows of tube feet
Sea Lilies and Feather Stars
• Sea lilies live attached to the substrate by a stalk
• Feather stars can crawl using long, flexible arms
Sea Cucumbers
• Lack spines, have a very reduced endoskeleton
• Five rows of tube feet; some of these are developed as feeding tentacles
Sea Daisies
• Sea daisies were discovered in 1986, and only three species are known
Chordates
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Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates
Chordates share many features of embryonic development with echinoderms, but have evolved
separately for at least 500 million years
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