Healthy individuals of Paramecium bursaria contain photosynthetic algal endosymbionts of the genus Chlorella. When within their hosts, the algae are referred to as zoochlorellae. In aquaria with light coming from only one side, P. bursaria gathers at the well-lit side, whereas other species of Paramecium gather at the opposite side. The zoochlorellae provide their hosts with glucose and oxygen, and P. bursaria provides its zoochlorellae with protection and motility. P. bursaria can lose its zoochlorellae in two ways: (1) if kept in darkness, the algae will die; and (2) if prey items (mostly bacteria) are absent from its habitat, P. bursaria will digest its zoochlorellae.
1) Which term most accurately describes the nutritional mode of healthy P. bursaria?
2) Which term accurately describes the behavior of Paramecium species that lack zoochlorellae in an aquarium with light coming from one side only?
3) Which term best describes the symbiotic relationship of well-fed P. bursaria to their zoochlorellae?
4) The motility that permits P. bursaria to move toward a light source is provided by
5) A P. bursaria cell that has lost its zoochlorellae is said to be aposymbiotic. It might be able to replenish its contingent of zoochlorellae by ingesting them without subsequently digesting them. Which of the following situations would be most favorable to the reestablishment of resident zoochlorellae, assuming compatible Chlorella are present in P. bursaria's habitat?
6) A P. bursaria cell that has lost its zoochlorellae is aposymbiotic. If aposymbiotic cells have population growth rates the same as those of healthy, zoochlorella-containing P. bursaria in well-lit environments with plenty of prey items, then such an observation would be consistent with which type of relationship?
7) Theoretically, P.bursaria can obtain zoochlorella either vertically (via the asexual reproduction of its mother cell) or horizontally (by ingesting free-living Chlorella from its habitat). Consider a P. bursaria cell containing zoochlorellae, but whose habitat lacks free-living Chlorella. If this cell subsequently undergoes many generations of asexual reproduction, if all of its daughter cells contain roughly the same number of zoochlorellae as it had originally contained, and if the zoochlorellae are all haploid and identical in appearance, then what is true?
A) The zoochlorellae also reproduced asexually, at an increasing rate over time.
B) The zoochlorellae also reproduced asexually, at a decreasing rate over time.
C) The zoochlorellae also reproduced asexually, at a fairly constant rate over time.
D) The zoochlorellae reproduced sexually, undergoing heteromorphic alternation of generations.
E) The zoochlorellae reproduced sexually, undergoing isomorphic alternation of generations.
l The origin of Eukaryotes
l The classification of Protists
l 3 of the more primitive groups of Protists
3 things that you should watch for in this lecture
l The way that eukaryotes have evolved from primitive ancestors
l The way that the organisms are classified and the factors that affect their classification
l The ways that protists can affect public health
Evolution of eukaryotes by serial endosymbiosis
l Nuclear membrane and endoplasmic reticulum formed from invagination of plasma membrane akin to phagocytosis
l Inclusion of organelles from phagocytosis of aerobic bacterium / cyanobacterium
l The origin of microtubule structures (flagellae, cilia, cytoskeleton) is unknown
l Ingestive (animal-like); protozoa
l Absorptive (fungus-like)
l Photosynthetic (plant-like); alga
The Endosymbionic Theory
l Mitochondria and chloroplasts were formerly from small prokaryotes living within larger cells (Margulis)
Protist Systematics & Phylogeny, I
l 1- Groups lacking mitochondria; early eukaryotic link; Giardia (human intestinal parasite; severe diarrhea); Trichomonas (human vaginal infection)
l 2- Euglenoids; autotrophic & heterotrophic flagellates; Trypanosoma (African sleeping sickness; tsetse fly)
l Alveolata: membrane-bound cavities (alveoli) under cell surfaces; dinoflagellates (phytoplankton); Plasmodium (malaria); ciliates (Paramecium)
l Stamenophila: water molds/mildews and heterokont (2 types of flagella) algae; numerous hair-like projections on the flagella; most molds are decomposers and mildews are parasites; algae include diatoms, golden, and brown forms
l Rhodophyta: red algae; no flagellated stages; phycobilin (red) pigment
l Chlorophyta: green algae; chloroplasts; gave rise to land plants; volvox, ulva
l Affinity uncertain:
l Rhizopods: unicellular with pseudopodia; amoebas
l Actinopods: ray foot (slender pseudopodia; heliozoans, radiolarians
l Mycetozoa: slime molds (not true fungi); use pseudopodia for locomotion and feeding; plasmodial and cellular slime molds
1. Nucleus formation
1. Nucleus formation
2. Origin of organelles
Features of Protists
l All eukaryotes
l Mostly unicellular
l Primitive and thought to have diverged early from a universal ancestor
l Very diverse
Types of Protist
l For many years, all organisms that did not conveniently fit into other groups were placed into the Protists.
l Classification is in a very active and dynamic state.
l Recently, molecular phylogeny based on similarity in DNA + electron microscopy has led to reclassification to give MONOPHYLETIC groups - organisms are grouped if they have a common ancestor.
Cellular Tree of Life
Summary of evolutionary relations
Ways of classifying Protists
ARCHEZOA (from Greek Arkhaios meaning ancient)
l Considered to be the most primitive of all eukaryotes
l No mitochondria (some engulf bacteria)
l Mostly parasitic (e.g. Giardia)
l 3 Sub-groups
Diplomonads (includes Giardia)
Trichomonads (e.g. Trichomonas)
l An important parasite
l Transmitted by both water and animals
l Probably the most important source of holiday diarrhea
l An STD
l 2 sub-groups
Photosynthetic but may be
heterotrophic or mixotrophic
Symbiotic or parasitic e.g. Trypanosoma, Leishmania
l Causes sleeping sickness in cattle and man in Africa transmitted by the Tsetse Fly
l In Americas, Chagas disease
Chagas disease / Sleeping Sickness
l What're the symptoms of sleeping sickness?
l Symptoms of sleeping sickness begin with fever, headaches, and joint pains. If untreated, the disease slowly overcomes the defences of the infected person, and symptoms spread to anaemia, endocrine problems, and cardiovascular and kidney disorders. The disease then enters a neurological phase when the parasite passes through the blood-brain barrier.
l The symptoms of the second phase is what gives the disease its name: besides confusion and reduced coordination, the sleep cycle is disturbed with bouts of lethargy punctuated with manic periods progressing to daytime somnolence and nighttime insomnia. Without treatment, the disease is fatal, with progressive mental deterioration leading to coma and death. Damage caused in the neurological phase can be irreversible.
l Life cycle involves biting/sucking insects
l The life cycles of members of the genus involve a vertebrate host (e.g., the human) and a vector (a sand fly) that transmits the parasite between vertebrate hosts
l Leishmania systemic disease, called visceral leishmaniasis, can have fatal complications. When introduced into the body by the bite of a sandfly, the parasite migrates to the bone marrow, spleen, and lymph nodes. The parasites damage the immune system by decreasing the numbers of disease-fighting cells.
l Systemic infection in children usually begins suddenly with vomiting, diarrhea, fever, and cough. In adults, fever for 2 weeks to 2 months is accompanied by nonspecific symptoms, such as fatigue, weakness, and loss of appetite. Weakness increases as the disease progresses.
l All have small membrane bound cavities (Alveoli) beneath the cell surface.
l 3 subgroups
l All have cilia for locomotion and feeding
l Reproduce by binary fission
l This genus contains many species, perhaps as many as 200, most of which are found as commensals or facultative or obligate parasites on aquatic invertebrates, fish,
l and amphibians.
l All parasites of animals
l All have a complex at the apex of the cell for penetrating host tissues (Apicomplex)
l Relict plastids possibly related to dinoflagellates with 4 bounding membranes
l Plasmodium falciparum
l Pneumocystis carinii (Pneumonia)
l Toxoplasma gondii (toxoplasmosis)
l Cryptosporidium parvum (cryptosporidosis)
Apicoplast (plastid of Apicomplexan)
l 4 membranes
l Genome of circular plasmid
l Smallest genome of any plastid (35kb)
l Codes for a number of genes
l Provides a means of attacking the parasite
Malaria - Plasmodium/mosquito
l Malaria causes a flu-like illness and these would include
l myalgia (limbs and back)
l abdominal pain
l loss of appetite
l orthostatic hypotension
l slight jaundice
l enlarged liver and spleen (sometimes not palpable)
Malaria - infection with an Apicomplexan, Plasmodium
l Abundant components of the phytoplankton
l Blooms cause red tides in coastal waters
l Can be an important symbiont in coral reefs
l Overview: A World in a Drop of Water
l Even a low-power microscope
Can reveal an astonishing menagerie of organisms in a drop of pond water
l These amazing organisms
Belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists
l Advances in eukaryotic systematics
Have caused the classification of protists to change significantly
l Protists are an extremely diverse assortment of eukaryotes
l Protists are more diverse than all other eukaryotes
And are no longer classified in a single kingdom
l Most protists are unicellular
And some are colonial or multicellular
l Protists, the most nutritionally diverse of all eukaryotes, include
Photoautotrophs, which contain chloroplasts
Heterotrophs, which absorb organic molecules or ingest larger food particles
Mixotrophs, which combine photosynthesis and heterotrophic nutrition
l Protist habitats are also diverse in habitat
And including freshwater and marine species
l Reproduction and life cycles
Are also highly varied among protists, with both sexual and asexual species
l A sample of protist diversity
l A sample of protist diversity
Endosymbiosis in Eukaryotic Evolution
l There is now considerable evidence
That much of protist diversity has its origins in endosymbiosis
l The plastid-bearing lineage of protists
Evolved into red algae and green algae
l On several occasions during eukaryotic evolution
Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested
l Diversity of plastids produced by secondary endosymbiosis
l : Diplomonads and parabasalids have modified mitochondria
l A tentative phylogeny of eukaryotes
Divides eukaryotes into many clades
l Diplomonads and parabasalids
Are adapted to anaerobic environments
Have mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymes
Have two nuclei and multiple flagella
l Parabasalids include trichomonads
Which move by means of flagella and an undulating part of the plasma membrane
l Euglenozoans have flagella with a unique internal structure
l Euglenozoa is a diverse clade that includes
Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites
l The main feature that distinguishes protists in this clade
Is the presence of a spiral or crystalline rod of unknown function inside their flagella
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
l The parasitic kinetoplastid Trypanosoma
Causes sleeping sickness in humans
Have one or two flagella that emerge from a pocket at one end of the cell
Store the glucose polymer paramylon
l The Euglenoids
No cell wall, thus changes shape as it moves.
Sub-membrane strips and membrane form pellicle.
Contains red eyespot.
Reproduction by cell division.
l Alveolates have sacs beneath the plasma membrane
l Members of the clade Alveolata
Have membrane-bounded sacs (alveoli) just under the plasma membrane
Are a diverse group of aquatic photoautotrophs and heterotrophs
Are abundant components of both marine and freshwater phytoplankton
Dinophyta /Pyrrhophyta or the Dinoflagellates Mostly unicellular with 2 unequal flagella , one that wraps around a groove in the middle of the cell, and the other that trails free, and include the non-motile zooxanthellae (found in corals).
The are most abundant in warm waters and second to diatoms in cold water.
l The Dinoflagellates
Contain two flagella.
One trails behind the cell.
Other encircles the cell at right angles.
Most have disc-shaped chloroplasts.
Contain xanthophyll pigments.
Many have tiny projectiles.
Many types of toxins produced. (Red Tides)
Characteristics of Dinoflagellates
1. Most are marine
2. Chlorophyll a, c, peridinin. Starch, oils , but can ingest food stuffs
3. Distinctive flagella pattern
4. Some without walls (naked) and others with walls (Armor) with cellulosic plates fitting together like armor which may have spines,
5. Half are colorless, some heterotrophic, sparophitic, phagocytic, parasitic and some photosynthetic. It is thought that through
evolution they have gained the ability to function as primary producers by "capturing" and using chloroplasts from other algae.
6. some bioluminescent
7. some responsible for red tides and 20 spp.. secrete toxins. They reproduce by simple cell division and form blooms that often color the water red, reddish-brown, yellow or unusual shades.
a. all toxic ones are photosynthetic
b. all are estuarine or neritic forms
c. all probably produce benthic, sexual resting stages
d. all capable of producing monospecific blooms (suggest competitive advantages through exclusion
e. all produce bioactive-watersoluable or lipid soluble toxins that are hemolytic, or neurotoxic in activity. (NSP, PSP, Dsp)
The Zooxanthellae are a variety of dinoflagellates which have developed a close association with an animal host. The hosts range from sponges to giant clams but the most important are the ones in the stony corals.
They help fix carbon through photosynthesis, release organic matter to be used by the coral, help in formation of the coral skeleton.
It was once believed that all zooxanthellae were the same species, Symbiodinium microadriaticum (Rowan and Powers, 1991). However, recently, zooxanthellae of various corals have been found to belong to at least 10 different algal taxa.
l Each has a characteristic shape
That in many species is reinforced by internal plates of cellulose
l Two flagella
Make them spin as they move through the water
l Rapid growth of some dinoflagellates
Is responsible for causing red tides, which can be toxic to humans
Are parasites of animals and some cause serious human diseases
Are so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues
Have a nonphotosynthetic plastid, the apicoplast
l Most apicomplexans have intricate life cycles
With both sexual and asexual stages that often require two or more different host species for completion
l Ciliates, a large varied group of protists
Are named for their use of cilia to move and feed
Have large macronuclei and small micronuclei
l The micronuclei
Function during conjugation, a sexual process that produces genetic variation
l Conjugation is separate from reproduction
Which generally occurs by binary fission
l Exploring structure and function in a ciliate
l : Stramenopiles have hairy and smooth flagella
l The clade Stramenopila
Includes several groups of heterotrophs as well as certain groups of algae
l Most stramenopiles
Have a hairy flagellum paired with a smooth flagellum
Oomycetes (Water Molds and Their Relatives)
Include water molds, white rusts, and downy mildews
Were once considered fungi based on morphological studies
l Most oomycetes
Are decomposers or parasites
Have filaments (hyphae) that facilitate nutrient uptake
l The ecological impact of oomycetes can be significant
Phytophthora infestans causes late blight of potatoes
l Diatoms are unicellular algae
With a unique two-part, glass-like wall of hydrated silica
l Diatoms are a major component of phytoplankton
And are highly diverse
l The Diatoms (Bacillariophyceae)
Among best known and economically most important members of this phylum.
Occur in both fresh and salt water.
Particularly abundant in colder marine habitats.
l1. Usually unicellular but chains do occur
l2. Pigments chlorophyll. a & c and fucoxanthin (gold/brown)
l3. Food reserve is chrysolaminarin and oils (buoyant)
l4. Only flagellate cells in reproduction (uniflagellate.)
l5. Walls made of glass called frustule.
l6. Looks like petri dish
7. Two symmetries..radial and bilateral which divide diatoms into 2 sub-divisions..Centric & Pennates
Reproduction...valve to valve...one product of the division retains the parental epivalve (top) and the other the parental hypovalve (bottom) which results in the bottom being slightly smaller than the parent because a new inside always grows back.
Reproduction in Diatoms
Continued vegetative reproduction reduces the size until it gets to its smallest size and this diploid cell produces gametes which fuse to form a full size zygote. Only the small cells will undergo sexual reproduction and if they get too small, they can't even do that.
l Accumulations of fossilized diatom walls
Compose much of the sediments known as diatomaceous earth
l Golden algae, or chrysophytes
Are named for their color, which results from their yellow and brown carotenoids
l The cells of golden algae
Are typically biflagellated, with both flagella attached near one end of the cell
l The Cryptomonads
Asymmetrical, unicellular marine and freshwater algae with two flagella.
Single two-lobed chloroplast with starch granules surrounding a central pyrenoid.
Reproduction by mitosis
l Most golden algae are unicellular
But some are colonial
l Brown algae, or phaeophytes
Are the largest and most complex algae
Are all multicellular, and most are marine
l Brown algae
Include many of the species commonly called seaweeds
Have the most complex multicellular anatomy of all algae
l Kelps, or giant seaweeds
Live in deep parts of the ocean
Human Uses of Seaweeds
l Many seaweeds
Are important commodities for humans
Are harvested for food
Alternation of Generations
l A variety of life cycles
Have evolved among the multicellular algae
l The most complex life cycles include an alternation of generations
The alternation of multicellular haploid and diploid forms
l The life cycle of the brown alga Laminaria
l Cercozoans and radiolarians have threadlike pseudopodia
l A newly recognized clade, Cercozoa
Contains a diversity of species that are among the organisms referred to as amoebas
l Amoebas were formerly defined as protists
That move and feed by means of pseudopodia
l Cercozoans are distinguished from most other amoebas
By their threadlike pseudopodia
l Foraminiferans, or forams
Are named for their porous, generally multichambered shells, called tests
l Pseudopodia extend through the pores in the test
l Foram tests in marine sediments
Form an extensive fossil record
l Radiolarians are marine protists
Whose tests are fused into one delicate piece, which is generally made of silica
That phagocytose microorganisms with their pseudopodia
l The pseudopodia of radiolarians, known as axopodia
Radiate from the central body
l : Amoebozoans have lobe-shaped pseudopodia
Are amoeba that have lobe-shaped, rather than threadlike, pseudopodia
Include gymnamoebas, entamoebas, and slime molds
Are common unicellular amoebozoans in soil as well as freshwater and marine environments
l Most gymnamoebas are heterotrophic
And actively seek and consume bacteria and other protists
Are parasites of vertebrates and some invertebrates
l Entamoeba histolytica
Causes amebic dysentery in humans
l Slime molds, or mycetozoans
Were once thought to be fungi
l Molecular systematics
Places slime molds in the clade Amoebozoa
Plasmodial Slime Molds
l Many species of plasmodial slime molds
Are brightly pigmented, usually yellow or orange
l The plasmodium
Is undivided by membranes and contains many diploid nuclei
Extends pseudopodia through decomposing material, engulfing food by phagocytosis
Cellular Slime Molds
l Cellular slime molds form multicellular aggregates
In which the cells remain separated by their membranes
l The Plasmodial Slime Molds
Totally without chlorophyll and are incapable of producing their own food.
Distinctly animal-like during much of life cycle, but fungus-like during reproduction.
Plasmodium converts into separate small sporangia (each containing spores) during times of significant environmental changes.
l The Cellular Slime Molds
About two dozen species of cellular slime molds are not closely related to the other slime molds.
Individual amoebalike cells feed independently, dividing and producing separate new cells periodically.
Human and Ecological Relevance
Break down organic particles to simpler substances.
l The Water Molds
Often found on dead insects.
Range in form from single spherical cells to branching, threadlike, coenocytic hyphae.
Coenocytic hyphae may form large thread masses (mycelia).
l Dictyostelium discoideum
Has become an experimental model for studying the evolution of multicellularity
l Green was the dominant color for plants both on land and in the ocean until about 250 million years ago when changes in the ocean's oxygen content - possibly sparked by a cataclysmic event - helped bring basic ocean plants with a red color to prominence - a status they retain today
l Studying ancient fossils plus current species of microscopic ocean plants called phytoplankton, the scientists found evidence that a "phytoplankton schism" took place after a global ocean oxygen depletion killed 85 percent of the organisms living in the ocean about 250 million years ago at the end of the Permian era. "This paved the way for the evolution of red phytoplankton,"
l "Plants on land are green, and they inherited the cell components that gave them a green color about 400 million years ago," Falkowski said. "But most of plants or phytoplankton in the ocean are red - they inherited their pigments about 250 million years ago.
l This suggests that a global ocean oxygen depletion changed the chemistry of the ocean and selected for red phytoplankton. The ocean has been dominated by the red line ever since."
l Red algae and green algae are the closest relatives of land plants
l Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont
And the photosynthetic descendants of this ancient protist evolved into red algae and green algae
l Red algae are reddish in color
Due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll
l Red algae
Are usually multicellular; the largest are seaweeds
Are the most abundant large algae in coastal waters of the tropics
lRhodophyta has more species of these than green and brown combined.
lIt has the highest commercial value, and don't get as large as brown algae.
absence of flagellate stages
presence of other pigments mainly phycobilins
l The Red Algae
Most species are seaweed.
Tend to occur in warmer and deeper waters than brown algae.
Most are filamentous.
Relatively complex life cycle involving three types of thallus structures.
Colors mostly due to phycobilins.
Numbers of species produce agar.
Floridean starch as food reserve (scattered throughout cells)
Existence of special female cells (carpogonia) and male gametes (called spermatia) for sexual reproduction.
Cell walls with inner rigid component and outer mucilage or slime layer. This is like the alginates and very valuable.
They can also deposit calcium carbonate (lime) into the walls of some species (Coralline algae) (Coralline algae)
l Green algae
Are named for their grass-green chloroplasts
Are divided into two main groups: chlorophytes and charophyceans
Are closely related to land plants
l The Green Algae
Includes about 7,500 species that occur in a rich variety of forms and occur in diverse, widespread habitats.
Greatest variety found in freshwater lakes, ponds, and streams.
Most have a single nucleus.
Most reproduce both sexually and asexually.
Chlorophyta..few marine planktonic reps. but lots of macroscopic, benthic types
Common inhabitant of freshwater pools.
Pair of whip-like flagella on one end pull the cell through the water.
Single, cup-shaped chloroplast with one or two pyrenoids inside.
Proteinaceous structures thought to contain starch synthesis enzymes.
l Asexual Reproduction
Nucleus divides by mitosis, and cell contents become two daughter cells within the cellulose wall.
Develop flagella and swim away.
Sexual Life Cycle of Chlamydomonas
Sexual Life Cycle of Chlamydomonas
Single row of cylindrical cells forming a filament.
Basal cell functions as a holdfast.
Ulothrix Life Cycle
Ulothrix Life Cycle
l Spirogyra (Watersilk)
Common freshwater algae consisting of unbranched filaments of cylindrical cells.
Frequently float in masses at the surface of quiet waters.
Fragmentation of existing filaments.
Papillae fuse and form conjugation tubes.
Spirogyra Sexual Reproduction
Epiphytic filamentous green alga.
Each cell contains a large, netlike chloroplast that rolls and forms a tube around and toward the periphery of each protoplast.
l Most chlorophytes
Live in fresh water, although many are marine
l Other chlorophytes
Live in damp soil, as symbionts in lichens, or in snow
l Chlorophytes include
Unicellular, colonial, and multicellular forms
Sponge Activity-What did you learn today?
l 1. In general, how do algae and protozoans differ? (Concept 28.1)
l 2 . _____ are eukaryotic autotrophs that float near the surface of water and are the basis of the food chain. (Concept 28.1
l 3. How does Euglena obtain energy? (Concept 28.3)
l 4. A sign on the beach states, "Beach Closed. Red Tide." The organisms interfering with your use of this beach are _____. (Concept 28.4)
l 5. Groups of seaweeds can generally be distinguished on the basis of _____. (Concept 28.5)