kingdom protista. 12.discuss the rationale for taxonomic reorganization of the kingdom protista...
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12. Discuss the rationale for taxonomic reorganization of the kingdom protista
13. Contrast the use of taxonomic “supergroups” with the traditional approach to classifying protists
14. Identify characteristics used to distinguish
groups of protists. Give some common examples
15. Identify the protistans most closely associated with Fungi, Plants, and Animals
Chapter 28 Objectives
Dating back to the 2 kingdom approach to taxonomy, some protists (“protozoa”) were classified with animals due to their ability to move, where other protists (“algae”) were classified as plants due to their ability to photosynthesize
Following that logic, the protozoa were further subdivided based on their means of locomotion, while the algae were largely categorized by their photosynthetic pigments
Traditional Protist Taxonomy
Ciliates – use ciliaFlagellates – use flagellaeAmoeboids – use pseudopodia Sporozoans – have no means of locomotion
Protozoa – Means of Locomotion
Modes of Protozoan Locomotion
CiliaRelatively
short and densely distributed over the surface of the cell
Modes of Protozoan Locomotion
FlagellaeLonger and
less numerous than cilia, but practically identical in internal structure
Structure of Cilia & Flagellae
Internal structure consists largely of bundles of microtubules in a “9+2” arrangement
9 pairs in a circular arrangement with 2 in the middle
Cilia and Flagellaehttp://www.youtube.com/watch?v=QGAm6hM
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Modes of Protozoan Locomotion
PseudopodiaLiterally “false
feet”Extensions of
the cytoplasm used not only for movement but also for feeding
Feeding and Movement of Amoebaehttp://www.youtube.com/watch?v=pvOz4V69
9gkhttp://www.youtube.com/watch?v=TOPMaNv
GTvchttp://www.youtube.com/watch?v=d_Bkg8euB
5Y
Modes of Protozoan Locomotion
Non-motileAll of these
types are parasitic and rely on a “vector” for movement to a new host
Different frequencies of light penetrate water differently, so red, yellow and brown pigments allow photosynthesis in deeper water, where green is restricted to shallower water
Blue-green Algae - actually prokaryotic cyanobacteriaGolden Algae – contain yellow and brown carotenoids Yellow Algae (diatoms) have silaceous cell wallsRed Algae – contain phycoerythrin . Some are
multicellular (note “nori” used to wrap sushi)Brown Algae – contain brown and olive colored
carotenoids. All are multicellular (note “kelp”)Green Algae – c0ntain chlorophyll A and B and have
cell walls made of cellulose
Algae - Photosynthetic pigments vary
The phylogenic approach to taxonomy demands that organisms are classified based on real ancestral divergences, and that the characteristics we use to distinguish the taxa are Homologous, not Analagous (“homoplasy”, or “homoplastic” in some textbooks)
Characteristics are homologous if they are derived from a common ancestry, even if they are modified to adapt to different functions or circumstances, or even diminished to the point of lacking a function (vestigial)
Analagous traits or structures are superficially similar, but evolved independently
The need for reorganization
Modern technology in biochemistry and electron microscopy reveals patterns impossible to observe by scientists of earlier generations
Many traits traditionally used for protist taxonomy are actually analagous. Photosynthesis has evolved independently in several lineages, as have pseudopodia for locomotion. In some lineages ancestral characters have diminished significantly, concealing the relationship between apparently distinct groups of organisms.
Interpretation can be tricky
A number of cellular organelles appear to be derived from ancient endosymbiosis events.
Organelles originating by endosymbiosis are recognized by several factors:One or more additional membranes Independent reproduction within the host cellDNA within the organelle itself (resembling bacterial
DNA)These organelles are believed to be the result of
endosymbiosis:MitochondriaCentriolesPlastids (Chloroplasts)
Endosymbiosis – The distinguishing character of Domain Eukarya
Primary vs. Secondary EndosymbiosisPrimary
Resulted from the engulfing of a prokaryotic cell which was retained as an organelle
Mitochondria and centrioles are the result of primary endosymbiosis
The chloroplasts of Red and Green Algae are primary endosymbionts
SecondaryResulted from the
engulfing of a primitive eukaryotic cell which was retained as an organelle.
Simply, it is like an organelle with organelles of its own
Chloroplasts of chromalveolates are secondary endosymbionts
See page 577, figure 28.2
1. Cite at least four examples of structural and functional diversity among protists
2. Summarize the role of endosymbiosis in eukaryotes
Concept Check 28.1, page 577
The supergroup approach eliminates the Kingdom Protista, and instead subdivides the Domain Eukarya into 5 ancestral lineages, each of which contains some members of the former Protist kingdom.
3 of the 5 supergroups contain only protists1 of the supergroups includes the Plants and
their closest protist relatives1 of the supergroups contains both Animals
and Fungi, and closely related protozoans
The “Supergroup” approach
As endosymbiosis events created the cellular organizations we recognize as Eukaryotes, variations in these fundamental structures form the differences between the supergroups
Variations in mitochondria, centrioles, cilia & flagellae, plastids and pseudopodia represent ancestral characters
These variations are more difficult to recognize than characteristics traditionally used for classification, but appear to be the real result of common ancestry – so it’s better, but harder to grasp at our level of study
Subdividing the Supergroups
Have diminished mitochondria that can function anaerobically and flagellae with additional crystalline rods
The name “excavate” comes from a groove (excavation) in the cell body
Familiar excavates include: Euglenoids – “mixotrophic” flagellates that can
photosynthesize, consume food by phagocytosis, and swim using flagella
Trypanosomes – parasitic flagellates that cause African Sleeping Sickness
Excavates
Appear to have originated as a result of a secondary endosymbiosis involving red algae
Some have chloroplasts resembling red algaeSome lack plastids, but have some residual
DNA homologous to plastid DNAThe chromalveolata are very diverse. One
subtaxon consists of traditional protozoans : ciliates, sporozoans and dinoflagellates (which are photosynthetic). The other subtaxon consists of a variety of algae: diatoms, golden algae and brown algae as well as the “water molds” which superficially resemble fungi
Chromoalveolata
#2. Would you expect the plastid DNA of photosynthetic dinoflagellates, diatoms, and golden algae to be more similar to the nuclear DNA of plants (Domain Eukarya) or to the chromosomal DNA of cyanobacteria (Domain Bacteria). Explain
Concept Check 28.3, page 589
Originally classified with the sarcodina (amoebae) due to the presence of pseudopodia
DNA analysis shows these organisms to be distinct from the amoebae
Pseudopodia in the Rhizaria are threadlike, rather than lobe shaped
Many have a cell wall or exoskeleton made of calcified organic material (the foraminiferans) or silica (the radiolarians)
Some also have flagellae, and may even be photosynthetic
Rhizaria
As implied by the “plastida” suffix, these organisms share a similar chloroplast structure.
The chloroplasts of these organisms originates from an ancient endosymbiosis with a cyanobacterium
This supergroup includes the red algae, green algae, and Kingdom Plantae
The plants appear to be descended from an ancestral green alga
Archaeplastida
#1. Contrast Red algae and Brown algae
#2. Why is it accurate to say that Ulva is truly multicellular but Caulerpa is not?
#3. Suggest a possible reason why species in the green algae lineage may have been more likely to colonize land than species in the red algae lineage
Concept Check 28.5, page 592
Unikonts include Kingdom Animalia, Kingdom Fungi, and their closest protozoan relatives
Unikonta is divided into 2 subtaxa, the Amoebozoa and the Opisthokonta
The Amoebozoa include the familiar amoebae (those with lobe shaped pseudopodia) and the slime molds
The Opisthokonta include the Kindgom Fungi, the Choanoflagellate protists, and the Kingdom Animalia
The animals appear to be descended from a choanoflagellate ancestor
Unikonta
Start individually and progress to small group (3)
Construct a matching set using the 5 supergroups as choices. Write 10 questions based on examples, structural features, etc.
Quiz the other members of your small groupCondense your question set and quiz a
second groupThe second group will also quiz your group.
Do page 599 #1-6 and #8
Review Activity