unicellular eukaryotes chapter 11. emergence of eukaryotes first evidence of life dates to 3.5...
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Emergence of Eukaryotes First evidence of life dates to 3.5 billion years
ago.First cells were bacteria-like.
Emergence of Eukaryotes Origin of complex eukaryote cells
Most likely symbiosis among prokaryotic cells.Modification of engulfed prokaryote into an
organelle: Primary endosymbiosis.Aerobic bacteria engulfed by bacteria.May have become mitochondria found in most
modern eukaryotic cells.Engulfed photosynthetic bacteria evolved into
chloroplasts.Descendants in green algae lineage gave rise to
multicellular plants.
Emergence of Eukaryotes Other groups apparently originated by
secondary endosymbiosis.One eukaryotic cell engulfed another eukaryotic cell
and the latter became transformed into an organelle.
ProtozoansProtozoa
Lack a cell wallHave at least one motile stage in life cycleMost ingest their foodCarry on all life activities within a single cell.Can survive only within narrow environmental
ranges.Very important ecologically.At least 10,000 species of protozoa are symbiotic in
or on other plants or animals.Relationships may be mutualistic, commensalistic, or
parasitic.
ProtozoansProtozoans are more diverse than all other
eukaryotes.No longer classified in a single kingdom.Recently shown that there are at least seven or more
clades.May be more than 60 monophyletic eukaryotic
clades.
“Protozoa” is now used informally without implying phyletic relationship.
Nutrition in ProtozoansAutotrophs - contain
chloroplasts.
Heterotrophs - absorb organic molecules or ingest larger food particles.Phagocytosis
Mixotrophs - combine photosynthesis and heterotrophic nutrition.
Protozoans Occur in Diverse Habitats
Freshwater and marine species.Require moisture
Free-living and symbiotic species.Mutualistic – benefits both.Commensalistic – one benefits,
the other is neutral.Parasitic – one benefits at a
cost to the other.
Locomotion in ProtozoansProtists have three
main methods of locomotion.
Some protists, like this Euglena, have one or two long flagella that they can whip around an propel themselves through the water.
http://www.youtube.com/watch?v=jl0TzaWUQWk
Locomotion in ProtozoansSome, like this
Tetrahymena, are covered with numerous, but shorter, cilia that facilitate movement and/or feeding.
http://www.youtube.com/watch?v=ApjDSGZWHsw
Locomotion in ProtozoansOthers use
ameboid movement to get around. A pseudopod is
extended forward, followed by the rest of the organism.
http://www.youtube.com/watch?v=7pR7TNzJ_pA
Form & Function - LocomotionCilia and flagella share
an internal structure of the axoneme (extending beyond the cell) consisting of 9 pairs of microtubules surrounding a central pair.
Inside the cell, the kinetosome consists of 9 triplets of microtubules just like centrioles.
Form & Function - LocomotionLobopodia – large
blunt extensions of the cell body.
Filopodia – are thin extensions, usually branching.
Reticulopodia – repeatedly rejoin to form a netlike mesh.
Form & Function - LocomotionAxopodia – long
thin pseudopodia supported by axial rods of microtubules.
Functional Components – Specialized Organelles
Nucleus – contains DNA.
Mitochondria – organelle used in energy production.
Golgi – part of the secretory system of the ER.
Plastids – organelles containing photosynthetic pigments.
Extrusomes – organelles that extrude something from the cell.
NutritionHolozoic feeders,
or phagotrophs, ingest particles of food.Food vacuole –
the membrane-bound vesicle containing the food.
Food vacuoles fuse with lysosomes containing digestive enzymes.
NutritionSaprozoic feeding
(ingestion of soluble food) may be by pinocytosis or by transport of solutes across the cell membrane.
Excretion and OsmoregulationContractile
vacuoles fill with fluid and then expel the fluid outside the cell.Function in
osmoregulation.More common in
freshwater species.
ReproductionFission is the cell
multiplication process in protozoa.Binary fission – one
individual splits into two equal sized individuals.
Budding – progeny cell much smaller than parent.
Multiple fission – multiple nuclear divisions followed by multiple cytoplasmic divisions producing several offspring.
ReproductionAll of above accompanied by some form of
mitosis.Mitosis in protozoa divisions varies from metazoan
mitosis.Nuclear membrane often persists.Spindle may form within the nuclear membrane.Centrioles not observed in ciliates.Macronucleus of ciliates elongates, constricts, and
divides without mitosis (amitosis).
ReproductionMany types of protists reproduce sexually as
well as asexually.Isogametes – all look alike.Anisogametes – two different types.
Syngamy – gametes from two individuals fuse to form the zygote.
Autogamy – gametes from one individual fuse.
Conjugation – gametic nuclei are exchanged.
CystsMany protists are
able to survive harsh conditions through the formation of cysts, dormant forms with resistant outer coverings and a shutdown of metabolism.
Major Protozoan TaxaAfter the eukaryotic cell evolved, diversification
followed, resulting in many clades.Opisthokonta is a very large clade characterized by a
combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells.Includes animals, fungi, chaonoflagellates and
microsporidians.
StramenopilaThe clade Stramenopila includes several
groups of heterotrophs as well as certain groups of algae.Most stramenopiles have a “hairy” flagellum
paired with a “smooth” flagellum.
ViridiplantaeThe clade
Viridiplantae contains unicellular and multicellular green algae, bryophytes and vascular plants.Phylum
Chlorophyta – single celled algae colonial forms.
ViridiplantaeVolvox is a colonial organism that shows a
division of labor where most cells are somatic cells concerned with nutrition & locomotion, but a few germ cells are responsible for reproduction. http://www.youtube.com/watch?v=9pjW1cMfTz8
EuglenozoaPhylum Euglenozoa is a
diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. Kinetoplastids & Euglenids.Persistence of nucleoli
during mitosis.Cell membrane contains
microtubules to stiffen it into a pellicle.
EuglenidsSubphylum Euglenida have one or two flagella that
emerge from a pocket at one end of the cell.Contain chloroplasts surrounded by a double membrane
– may have arisen by secondary endosymbiosis.
KinetoplastidsSubphylum
Kinetoplasta have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast.Include free-living
consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems.
Others are parasitic.Trypanosoma
RetortamonadsPhylum Retortamonada includes commensal
and parasitic unicells.Lack mitochondria & Golgi
DiplomonadsPhylum Retortamonada: Diplomonads:
Are adapted to anaerobic environments.Lack plastids.Lack mitochondria but may have mitochondrial genes in
the nucleus.
Diplomonads have two nuclei and multiple flagella.Giardia
ParabasalidsParabasalids move by means of flagella and
an undulating part of the plasma membrane.This clade may have diverged from the main
eukaryotic clade very early.Trichomonas
AlveolataMembers of the
clade (superphylum) Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane.Dinoflagellates,
apicomplexans, ciliates.
Alveolata - CiliatesMembers of the
phylum Ciliophora use cilia to move and feed.
Ciliates have large macronuclei and small micronuclei.
Alveolata - CiliatesCiliates are a large, varied group of protists.
http://www.youtube.com/watch?v=yO0tRvYEXGc&feature=player_embedded
Alveolata - CiliatesCiliates are structurally complex.All ciliates have a kinety system made up of
the cilia, kinetosomes and other fibrils.Many have structures that can be expelled
such as trichocysts and toxicysts.Defensive function
Alveolata – Types of CiliatesSuctorians – ciliates that lose cilia as adults, grow a
stalk and become sessile.Use tubelike tentacles for feeding.
Symbiotic ciliates – some commensal, others parasitic.
Free-living ciliates – may be swimmers, or sessile.Stentor, Vorticella, Paramecium
Alveolata – Reproduction in Paramecium
Paramecium, as well as many other protists, reproduce asexually by binary fission.
Alveolata – Reproduction in Paramecium
Conjugation is a sexual process that produces genetic variation.
Conjugation is separate from reproduction which generally occurs by binary fission.
http://www.youtube.com/watch?v=rgkgD4XcqTk&feature=related
Alveolata – DinoflagellatesPhylum Dinoflagellata is a diverse group of
aquatic photoautotrophs and heterotrophs.Abundant in both marine and freshwater
phytoplankton.
Alveolata – DinoflagellatesEach has a
characteristic shape that in many species is reinforced by internal plates of cellulose.
Two flagella make them spin as they move through the water.
Alveolata – DinoflagellatesRapid growth of
some dinoflagellates is responsible for causing “red tides,” which can be toxic to humans.
California Noctiluca Bloom
http://www.whoi.edu/redtide/index.html
Alveolata – DinoflagellatesSome dinoflagellates are bioluminescent.
Others live symbiotically with corals (zooxanthellae).
Alveolata – ApicomplexansApicomplexans are
parasites of animals and some cause serious human diseases.Named because one
end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues.
Have a non-photosynthetic plastid, the apicoplast.
Alveolata – ApicomplexansMost
apicomplexans have intricate life cycles with both sexual and asexual stages that often require two or more different host species for completion.
AmoebozoaAmebas are found
in fresh and salt water as well as moist soil.
An ameba feeds by wrapping a pseudopod around its food – phagocytosis.
EntamoebasEntamoebas are parasites of vertebrates and
some invertebrates.Entamoeba histolytica causes amebic dysentery in
humans.
Foraminifera
This Phylum has slender pseudopodia that extend through openings in the test, then branch and run together forming a net (reticulopodia).
Foraminiferans, or forams are named for their porous, generally multichambered shells, called tests.
ForaminiferaPseudopodia extend through the pores in the test.
Foram tests in marine sediments form an extensive fossil record.
RadiolariaRadiolaria refers to marine testate ameba with
intricate skeletons.They have very diverse and beautiful forms.Useful for determining the age of rock strata.
Phylogeny and Adaptive Diversification
Phylum Retortamonada
Phylum Diplomonadea
Phylum Parabasala Order Trichomonadida
Phylum Euglenozoa Subphylum Euglenida
Class Euglenoidea Subphylum Kinetoplasta
Class Trypanosomatidea
Phylum Stramenopiles
Phylum Ciliophora
Phylum Dinoflagellata
Phylum Apicomplexa
Class Gregarinea
Class Coccidea
Phylum Foraminifera
Phylum Radiololaria
Phylum Viridiplantae
Phylum Amoebozoa
Phylum Opisthokonta