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Lecture VIII Protistans
Source: Freeman (2002)
surface
waters teem
with
microscopic
protists
In some
near-shore
areas,
gigantic
protists from
underwater
forests
Protists are
particularly
abundant in
tidal habitats
Morphologies and lifestyles found among protists. Protists are abundant in a wide
variety of aquatic habitats. In marine environments, they are found in open ocean
as well as in near-shore intertidal habitats (Freeman 2002)
Euglena
Eugleazoa includes both photosynthetic and heterotrophic
flagellates. Most are autotrophic, but the lineage includes
Trypanosoma
Ciliates
dinoflagellates
Alvoelata are unicellular, and bear a cavity called and
“alveoli”. Diverse in body form.
Apicompla
water molds
diatoms
brown
algae
Stramenopilan are a diverse lineage of heterotrophs and
phothynthetic forms (algae). The name refers to fine hairs
on the flagella of members of this lineage
Rhodophyta are red algae – unlike other eukaryotic algae,
they lack flagella at any stage in their life history. They are
the most abundant algae in tropical coastal areas
Dulce, a large, edible red algae
Volvox colonies
Sea lettuce
Green Algae and Plants evolved from a common
photoautotrophic ancestor. Over 7000 species, mostly fresh
water.
Desmid
Choanoflagellida Flagellate protists. Possible ancestor
to Sponges – to Animals.
Source Solomon et al 2002
Lecture Themes
structure and function; ecurring evolutionary themes and
unifying features
the origin of mitochondria and chloroplasts
Impact of Protists on Human Health and Welfare
“The key to understanding the protists is to recognize that a series of important
innovations occurred, often repeatedly, as eukaryoites diversified.” (Freeman 2002)
Size and Structure of Eukaryotic Cells compartmentalization
and differentiation makes large size possible.
Problem: transport and exchange
limitations with increasing size
Solution: compartmentalization
Example: Paramecium
Eukayotic compartments;
nucleus, peroxisomes,
mitochondria, chloroplasts,
central vacuole, golgi, rough ER,
smooth ER
Paramecium, a predaceous protist that feeds on
prokaryotes and other protists
Nutritional and Metabolic Diversity in Protists
Ingestive Lifestyles:
Predation and Scavengers
Absorbtive Lifestyles;
Decomposers and Parasites
Photosynthetic Lifestyles;
Producers, many of which
are symbionts
Photosynthetic unicellular dinoflagellates
Paramecium
Giardia, a unicellular human parasite
giant kelp
Parasitism
Predation and Scavenging
pseudopodia engulf food
Symbiosis
host
symbionts
Green cells are
dinoflagellates inside a
heliozoan
Ciliary currents sweepd food into
gullet
host parasite
the parasite is a red
algae – with
nonpigmented cells
Photosynthetic pigments
Red: chlorophyll a
and phycobilins
Brown: chlorophyll a
and chlorophyll c
Green: chlorophyll
a and chlorophyll b
Many photosynthetic groups of algae are distinguished by the accessory
pigments they contain, in addition to chlorophyll a. Each of these
accessory pigments interecpts different wavelengths of light
Consider the diversity of feeding
modes in the lineage Alveolata
Ciliates
-many predators and herbivores
-some parasite/basorbers (eg cattle
guts, fish gills)
-some feed via symbiotic
photosynthesizers
Dinoflagellates
-half or so are photosynthetic, many
others are parasitic
Apicomplexans
-most apicomplexans are parasitic
Feeding diversity in protists, like electron donor and electron
acceptor diversity in prokaryotes, no doubt drove phylogenetic
diversification
Locomotion and Structures
for Support and Protection
Modes of Locomotion in Protists
Pseudopodia
An Amoeboid Protist
flagella
cilia
Structure of microtubules in cilia and flagella
A ciliatedProtist
2 single microtubules
(red) surrounded by
nine paired
microtubules (yellow)
A ciliated protist
reference: chapter 4 in textbook
Paramecium can swim in either
direction relative to its long axis by
beating its cilia in rhythmic,
coordinated fashion that progresses
from one end of the cell to the
other.
Amoeba extends a pseudopodium toward a Pandorina colony. At right, the
amoeba surrounds colony before engulfing it
Source: Hickman et al 2001
Proposed mechanism of psuedopodial
movement. In endoplasm, actin subunits
are bound to regulatory proteins that keep
them from assembling.
Sources: Purves et al (2002), Freeman (2002)
External Structures for Support
and Protection
Forams; shells are made
from protein hardened
with calcium carbonate
Radiolarians; glassy skeletons
allow light penetration for
photosynthetic endosymbionts
Amoeba; shell made
of cemented sand
grains
foraminiferan with
calcium carbonate
tests
diatomshave glasslike silicon containg
sructures
Diatoms
Multicellularity
Dinoflaggelates
surrounded by
cellulose plates
Source: Freeman 2002
True multicellarity is defined functionally
Differentiation of cell function (specialization, division of labor)
Differential gene expression
Multicellularity has evolved independently multiple times in
Protistan lineages
Multicelluarity confers advantages by allowing for increased size,
specialization, and complexity
The initial evolution towards multicellularity begins with differentiation
of gamete-producing cells, the consequence of the uniquely eukaryotic
reduction division process; meiosis
Clamydomonas
Gonum
Pandorina
Multicellular Green Alga
(Coleochaete orbiculairs)
Volvox
Morphological continuum in Volvocales from unicellular to multicelluar.
Reproduction, Life Cycles and Alternation of Generations
Meiosis and Sexual
reproduction were
important Protistan
innovations
Life Cycle of Chlamydomonas
Life Cycle of a cellular slime mold (Dictyostelium)