Kingdom Protista

AP Biology

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

ysTA

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

#1. Contrast the pseudopodia of amoebozoans and forams

Concept Check 28.6, page 596

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