Even a low-power microscope
–Can reveal an astonishing menagerie of
organisms in a drop of pond water
•Protists are more diverse than all other
–And are no longer classified in a single
•Most protists are unicellular
–And some are colonial or multi-cellular
• Organisms that range in size from
single cells to complex structures
more than 100 meters long.
• They show a variety of reproductive
and nutritional strategies.
•Protists, the most nutritionally diverse of all
–Photoautotrophs, which contain chloroplasts
–Heterotrophs, which absorb organic molecules
or ingest larger food particles
–Mixotrophs, which combine photosynthesis and
Protists are also diverse in habitat
•Including freshwater and marine species
(a) The freshwater ciliate Stentor,
a unicellular protozoan (LM)
(b) Ceratium tripos, a unicellular marine dinoflagellate (LM)
(c) Delesseria sanguinea, a multicellular marine red alga
(d) Spirogyra, a filamentous freshwater green alga (inset LM)
•There is now
–That much of
has its origins in
•The plastid-bearing lineage of protists
–Evolved into red algae and green algae
•On several occasions during eukaryotic
–Red algae and green algae underwent
secondary endosymbiosis, in which they
themselves were ingested
2˚ Endosymbiosis Plastid
Cyanobacterium Red algae Ciliates
Diplomonadida and parabasala
•Have modified mitochondria
–Are adapted to anaerobic environments
–Have mitochondria that lack DNA, an electron
transport chain, or citric-acid cycle enzymes
•A tentative phylogeny of eukaryotes
–Divides eukaryotes into many clades
–Have two nuclei and multiple flagella
(a) Giardia intestinalis, a diplomonad (colorized SEM)
· Move by flagella
· They may enter into symbiotic
relationships with other organisms.
–Which move by means of flagella and an
undulating part of the plasma membrane
•Have flagella with a unique internal structure
•Euglenozoa is a diverse clade that includes
–Predatory heterotrophs, photosynthetic
autotrophs, and pathogenic parasites
–Kinetoplastids & Euglenids
•The main feature that distinguishes protists
in this clade
–Is the presence of a spiral or crystalline rod
of unknown function inside their flagella
Ring of microtubules
–Have a single, large mitochondrion that
contains an organized mass of DNA called a
–Include free-living consumers of bacteria in
freshwater, marine, and moist terrestrial
–Causes sleeping sickness in humans
organelle that functions
as a light shield, allowing Light detector: swelling near the
light from only a certain base of the long flagellum; detects
direction to strike the light that is not blocked by the
light detector eyespot; as a result, Euglena moves
toward light of appropriate
intensity, an important adaptation
Short flagellum that enhances photosynthesis
Nucleus Contractile vacuole
Pellicle: protein bands beneath
the plasma membrane that Chloroplast
provide strength and flexibility
Figure 28.8 (Euglena lacks a cell wall) Paramylon granule
Only one third of the species of Euglenoids are
· Euglena stores glucose in a polymer called Paramylon
An eyespot with a photoreceptor is capable of
detecting the presence of light.
Reproduction is asexual.
Members of the clade Alveolata
–Have membrane-bounded sacs (alveoli) just
under the plasma membrane
0.2 µm Flagellum
–Are a diverse group of aquatic
photoautotrophs and heterotrophs
–Are abundant components of both marine
and freshwater phytoplankton
•Shape is reinforced by internal plates of cellulose
–Make them spin as they
–move through the water
Some species are responsible for red tides that kill fish
–Are parasites of animals and some cause serious
–Are so 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
Most apicomplexans have intricate life cycles
–With both sexual and asexual stages that often require
two or more different host species for completion
–Plasmodium causes malaria
• Complicated life cycle that usually involves the
formation of infective spores.
e.g. malaria - The parasite is injected into a
human by a mosquito. The parasite then invades
red blood cells and ruptures them.
–Are named for their use of cilia to move and feed
–Have large macronuclei and small micronuclei
–Function during conjugation, a sexual process that
produces genetic variation
•Conjugation is separate from reproduction
–Which generally occurs by binary fission
• Example - Paramecium
• The outer covering of paramecium is covered
with hundreds of cilia
• They have numerous organelles including a
gullet (oral groove) and an anal pore
• The macronucleus controls the cell's activities.
• The micronucleus is involved in cell reproduction
(sexual & asexual).
CONJUGATION AND REPRODUCTION
Meiosis of micronuclei
produces four haploid
micronuclei in each cell. 3 micronuclei in each cell
disintegrate. The remaining
MEIOSIS micro-nucleus in each cell
divides by mitosis
The cells swap
Two rounds of cytokinesis The original macro- forming a diploid
partition one macronucleus 8
nucleus disintegrates. 7 micronucleus.
and one micronucleus Four micronuclei Key
into each of four daughter cells. while the other four Three rounds of Conjugation
remain micronuclei. mitosis without Reproduction
FEEDING, WASTE REMOVAL, AND WATER BALANCE
Stentor (Type of ciliate)
•Stramenopiles have “hairy” and smooth
•The clade Stramenopila Includes:
–Golden algae Smooth
–Brown algae 5 µm
–Include water molds, white rusts, and downy
–Were once considered fungi based on
–Are decomposers or parasites
–Have filaments (hyphae) that facilitate nutrient
–Have cell walls
made of cellulose
•Are unicellular algae
–With a unique two-part, glass-like wall of
–major component of phytoplankton
· Most numerous unicellular algae in the oceans
and are an important source of food and
· Also important in freshwater environments.
· Glucose stored as polysaccharide laminarin (Same
as golden & brown algae)
· Their remains form diatomaceous earth.
~ 100 000 species
–Are named for their color,
which results from their
yellow & brown carotenoids
•The cells of golden algae
–Are typically bi-flagellated, with both flagella
attached near one end of the cell
–Are the largest and most complex algae
–Are all multicellular, and most are marine
–Include many of the species commonly called
–Have the most complex multi-cellular anatomy of
Photosynthetic & multicellular Blade
· Range in size.
Many are 50-100 m long.
· Found along rocky shores
The thalus (plant like body) contains: Holdfast
· Holdfasts for attachment
· Blades and air bladders that function in floatation
· A stem-like structure that holds the blades is called a
Common "seaweed" found along the rocky coast.
•Kelps, or giant seaweeds
–Live in deep parts of the ocean
–Can grow as long as 60m
Cell walls are composed of
cellulose and gel forming
cushion the algae in the
Brown Algae - Macrocystis and
Nereocystis (Deep water Kelp)
A variety of life cycles
Have evolved among the multi-cellular algae
cycles include an
alternation of Sporophyte
•Cercozoans and radiolarians have threadlike
•A newly recognized clade, Cercozoa
–Contains a diversity of species that are among
the organisms referred to as amoebas
•Amoebas were formerly defined as protists
–That move and feed by means of pseudopodia
•Cercozoans are distinguished from most other
Foraminiferans, or forams
–Are named for their porous, generally
multichambered shells, called tests
Pseudopodia extend through the pores in the test
–Whose tests are fused into one delicate piece,
which is generally made of silica
–Phagocytize microorganisms with their
•The pseudopodia of radiolarians, known as
–Radiate from the central body
Marine plankton (float in marine environments) with
a skeleton composed of silica, and numerous needle-
• Have lobe-shaped pseudopodia
–rather than threadlike, pseudopodia
–Include gymnamoebas, entamoebas, and slime
· Do not have a cell wall
· Usually motile
· Food vacuoles
· Contractile vacuole (water elimination)
Reproduction is usually asexual but many also reproduce
sexually during some part of their life cycle.
–Are common unicellular amoebozoans in soil as
well as freshwater and marine environments
•Most are 40 µm
–And actively seek
–Are parasites of vertebrates and some invertebrates
–Causes amebic dysentery in humans
Move by cytoplasmic extensions called pseudopodia.
Feed by phagocytizing (engulfing) their prey.
Most amoeboids are marine organisms;
Amoeba proteus is found in freshwater
Slime molds, or mycetozoans
–Were once thought to be fungi
–Places slime molds in the clade Amoebozoa
–Plasmodial & Cellular types
–Is undivided by membranes and contains
many diploid nuclei
–Extends pseudopodia through
decomposing material, engulfing food by
Protists that are Decomposers
· Slime molds play an ecological role similar to that of fungi.
· They are decomposers, feeding on dead organic material.
· They differ from fungi in that slime molds ingest their food.
· Slime molds are masses that creep along the substrate and phagocytize
dead organic material and microorganisms.
· The mass is one large cell referred to as a plasmodium.
· Spores are resistant to environmental extremes (Food and moisture)
and germinate when environmental conditions become favorable
· Saprotrophic; they live off of dead organic matter.
Plasmodial Slime mold life cycle
(preparing to fruit)
Amoeboid cells Mature
Germinating Spores MEIOSIS
(n) Haploid (n)
Flagellated cells Diploid (2n)
Cellular slime molds
•Form multicellular aggregates
–In which the cells remain separated by their
–Has become an
Cellular Slime Mold Life Cycle
600 µm MEIOSIS
200 µm Diploid (2n)
The word algae refers to aquatic (freshwater or marine)
Algae photosynthesize like plants. They produce much
of the oxygen in the atmosphere.
· Algae provide food for aquatic food chains.
Red & Green Algae
•Are the closest relatives of land plants
•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
• Are reddish in color
–Due to an accessory pigment call phycoerythrin,
which masks the green of chlorophyll
• Red algae are found mainly in warmer, tropical oceans.
• Accessory photosynthetic pigments are called
phycobilins which allow some species to survive in deep
waters where blue and green light predominates.
• Some species are filamentous but most have a complex
pattern of branching.
• Some coralline forms deposit calcium carbonate in
their cell walls, making coral reefs.
–Are named for their grass-green chloroplasts
–Are divided into two main groups: chlorophytes
–Are closely related to land plants
Single-celled and multicellular forms.
Ancestors of the first plants, both have the following
characteristics in common:
They have a cell wall that contains cellulose.
They have chlorophyll
They store their food as starch inside the chloroplast.
• Multicellular with a leaf-like body that is
two cells thick but up to one meter long
• Common name: Sea lettuce
· Colonial green algae
· They divide asexually to
produce a daughter colony.
Notice the daughter colonies
within the larger colonies.
• Some cells are specialized to produce sperm
and eggs for sexual reproduction which is a
characteristic of multicellular organisms.
• Considered to be a colony because it appears
to be intermediate between a group of
individual cells and a multicellular organism.
· Filamentous form of green algae.
· Has a ribbonlike spiral-shaped chloroplast.
· Sexual reproduction occurs by conjugation.
The zygote is resistant and overwinters.
Chlorophyte Life Cycle
Regions REPRODUCTION REPRODUCTION
of single Zygote
Key + MEIOSIS
Protists Compared to Plants,
Animals, and Fungi
• Characteristics resemble plants, animals, or fungi.
• Photosynthetic protists differ from plants in that they do
not have structures that protect the gametes or zygote.
• Plants and animals undergo a period of embryonic
development but protists do not.
• Fungi have cell walls composed of chitin; protists do not
have chitin in their cell walls
• Fungi do not have cilia or flagella. Many kinds of protists
have cilia or flagella.
· green algae · amoeboids
· brown algae · ciliates
· red algae · zooflagellates
· diatoms · sporozoans
· dinoflagellates · slime molds