Transcript Protists in class

Protistans
Chapter 22
Characteristics of Protistans
• Have a nucleus and organelles
(eukaryotes)
• Protists are mainly defined by what
they are not - they are not bacteria
or fungi, they are not plants or
animals.
•
•
•
•
•
•
Some protists are autotrophs
Some protists are heterotrophs
Some are parasitic.
Some are decomposers.
Most protists are aerobic.
They can be unicellular, multicellular, or
colonial.
• Many live in water or moist environments.
• Protists reproduce asexually by binary
fission, and a few species are capable of
sexual reproduction. Many have very
complex life cycles.
• Protists are so small that they do not
need any special organs to exchange
gases or excrete wastes. They rely on
simple diffusion.
• Protists eat by phagocytosis
(endocytosis) - they engulf their food in
their cell membrane, and pinch off a
section of membrane to form a vacuole
• contractile vacuole, which drains the cell
of waste products (especially excess
water in freshwater species osmoregulation) and squirts them outside
the cell.
• Classification
– Old Classification based on modes of nutrition,
pigments (if present), carbohydrate food
reserves, flagella, cell wall components and the
environments they inhabit
– New classification based on phylogeny, still being
worked on
– We will look mostly to the “old” classification
• Importance
– Important components of food chains. E.g.
kelp beds are among the most productive
ecosystems on earth
– Unicellular aquatic Protista (plankton) form
a very important component of the food
chain. The photosynthetic ones are called
phytoplankton and the heterotrophic ones
are called zooplankton (which also includes
many animal larvae or tiny crustaceans)
– Also, many are used by humans in industry
• Classification (phyla)
– we will look at 14
• Generally grouped by “feeding” style into
one of three categories
– Protozoans – animal like, unicellular,
heterotrophs
– Algae – plant like, autotrophs
– Fungus -like
Protozoans – animal like, unicellular,
heterotrophs. (4 phyla)
1. Sarcodina – Amoeba like, move with
pseudopods . They extend part their body in a
certain direction, forming a pseudopod or false
foot, and then flow into that extension
(cytoplasmic streaming). They change shape.
No cell wall. In water. Some have shells
(foraminiferans and radiolarians). Asexual
reproduction . They eat other protozoans,
algae, and even tiny critters like rotifers. Many
sarcodines are parasites.
2. Zoomastigina – Flagellates, move with
long flagella
• Flagellates: The flagellates are motile by
means of whip-like structures called flagella,
attached to the surface of the cell. The
eukaryotic flagella is completely different in
structure and action from the bacterial.
Eukaryotic flagella move in a wave-like or
whip-like motion that propels the cell forward.
• Some biologists include Euglena here,
others include it with the algae. We will
include them with algae.
3. Ciliophora- Unicellular, heterotrophic
ciliates. Aquatic. These ciliates move by
means of numerous small cilia. Cilia are
short, hair-like structures that cover the
surface of the ciliate cell. The beat back
and forth in unison, propeling the cell
rapidly through the water. They are
complex little critters, with lots of
organelles and specialized structures.
Many of them, like Paramecium, even
have little toxic threads or darts that they
can discharge to defend themselves.
4. Sporozoans – parasite, non-motile, produce
spores
– Also called Apicomplexa
– parasitic
– They typically have complex life cycles with both
sexual and asexual stages. Different stages
often develop in different host species. Their life
cycles involve intermediate hosts such as the
mosquito. They form small resistant spores,
infective bodies that are passed from one host
to the next. In more general terms, spores are
haploid reproductive cells that can develop
directly into adults. (toxoplasmosis and malaria)
Algae – plant like protist
• (Photosynthetic protists), Major producers in aquatic
ecosystem
• Unicellular, colonial & multicellular, photosynthetic,
possess chloroplasts (although some are
heterotrophic)
• Unicellular forms known as phytoplankton.
• Classified into six or 7 phyla –Differences between
groups are due to diversity in photosynthetic
pigments, carbohydrates food reserves, number
and position of flagella, life cycle patterns and cell
wall characteristics.
• 1. Euglenophyta – euglenoids, unicellular, aquatic, have
traits of both plants and animals, lack cell wall, contain
chlorophyll & do photosynthesis. Eyespot, flagella, can
ingest food. Both autotrophic and heterotrophic. Mostly
found in freshwater.
• Instead of a cell wall they have a pellicle, a flexible layer of
interlocking proteinaceous strips inside plasma membrane
• Reproduction via simple cell division. Sexual reproduction
is lacking.
• This organism may actually have resulted from
endosymbiosis, in which an ancestral form engulfed a green
algal cell. Appears they are derived from protozoa by
incorporation of chloroplasts. (If grown under proper conditions cells
may replicate faster than the chloroplasts, giving rise to non-photosynthetic cells
which are nearly indistinguishable from protozoa. The heterotrophs ingest food. )
Euglenoid Body Plan
long flagellum
contractile vacuole
chloroplast
Figure 22.3
Page 365
eyespot
nucleus
nucleus
ER
Figure 22.3
Page 365
Golgi body
mitochondrion pellicle
• 2. Diatoms – phylum bacillariophyta, unicellular, with
shells made of silica, autotrophs, in both fresh and salt
water. Mostly unicellular but a few colonials. Most
autotrophic, a few are heterotrophic. Lack flagella.
• Cell walls, called frustules, are polymerized, opaline silica
(glass like). The two halves of the frustules fit together
like a Petri dish.
• Reproduction mainly asexual. The two halves of the
frustules open and each side generates a new half. Sexual
reproduction may take place.
• Diatoms are so abundant that the photosynthesis of
diatoms accounts for a large percentage of the oxygen
added to the atmosphere each year from natural sources.
• Some books still place them with the Chrysophyta, the
golden-brown algae, but they are now recognized as an
entirely separate group.
•
•
•
•
•
3. Chrysophyta - golden-brown algae
Cell wall of cellulose and silica
Food storage of lipid and laminarin
Unicellular or colonial
2 flagella (unequal length)
• 4. dinoflagellates – Phylum Pyrrophyta , unicellular
with cell walls, 2 flagella, they spin when flagella beat,
some in fresh but most in salt water, some are
bioluminescent, red or orange usually, cause “red
tides” when population booms, some produce toxins.
• Dinoflagellates are named after their two flagella,
which lie along grooves, one like a belt and one like a
tail.
• Many species have a heavy armor of cellulose plates,
often encrusted with silica.
• Some dinoflagellate species often form algal blooms
in coastal waters, building up enormous populations
visible from a great distance.
• The amazingly potent toxins, that about 20 species
produce, poison shellfish, fish, and marine mammals,
causing the deadly red tide.
• 5. red algae – phylum rhodophyta, red seaweeds,
multicellular, marine (warm tropical waters), attach to rocks
by structures called hold fasts, some have pigments other
than chlorophyll that allow them to photosynthesize in
deeper water where only green, violet and blue light
penetrate. Usually grow attached to rocks or other algae,
but there are a few free floating forms and a few unicellular
or colonial forms.
• No flagellated cells at all in life cycle.
• Floridean starch carbohydrate food reserve is more
glycogen like (found in animals and fungi) than other plant
starches.
• Cell walls of cellulose or other polysaccharides, plus
gelatinous pectic materials, e.g. agar and carrageenan
(sulfated polymers of galactose). Some species deposit
calcium carbonate in their cell walls, called coralline algae.
• 6. brown algae – phylum phaeophyta, mostly cool
saltwater on rocky coasts, attached to rocks by holdfasts ,
free floating forms, Some also have air bladders for
flotation, brown color, multicellular
• This algal division includes the largest multicellular algae
(and largest protists ). They show the greatest division of
labor between cells seen in any algal phyla. In fact the larger
kelp species have a primitive type of phloem tissue
• Only reproductive cells have flagella,
• Like all algae, their blades are thin because they lack the
complex conductive tissues of green plants, and must rely
on simple diffusion.
7. green algae – phylum chlorophyta, chlorophyll is major
pigment, most freshwater. The green algae are a diverse
group. They share many characteristics with plants.
Most are multicellular, but there are a few unicellular
forms.
• Both plants and green algae:
– have cell walls made of cellulose and hemicellose and
pectin
– both groups of organisms use starch as the type of
substance used to store energy
– they have the same combination of pigments: chlorophyll
a, chlorophyll b, and various carotenoids (eg betacarotene, xanthophylls).
• Due to these similarities (as well as other sources of
evidence) it is believed that higher plants evolved from an
ancient species of green algae.
Fungus-like protist
• slime molds and water molds and
downy mildew, obtain energy from
decaying organic material, live in cool
moist places,
• 3 phyla – 2 are slime molds and the
other is a watermold/downy mildew.
1. plasmoidial slime molds – phylum myxomycota
“acellular” slime molds. Terrestrial, Heterotrophic.
• The body form of this organism during most of its life
is a multinucleated mass of cytoplasm (a type of
coenocytium).
• Lack cell walls –
• exist as streaming masses of naked protoplasm which
"creeps", As they travel they engulf bacteria, yeast
cells, fungal spores and decayed plant and animal
matter. The plasmodium contains many nuclei which
undergo synchronous divisions.
• Sexual reproduction involves the fusion of amoebae
and/or flagellated gametes which come from spores
produced within sporangia.
• 2. cellular slime molds – phylum
acrasiomycota , This phylum contains the
cellular slime molds. Unlike the Myxomycota,
the cellular slime molds consist of ameoba-like
cells each containing a single nucleus.
Chemical signals from the cells can cause them
to aggregate into a mass that resembles a
plasmodium, although the individual nuclei
remain separated by their plasma membranes.
• 3. water molds and downy mildew – phylum
oomycota . These organisms grow as cottony, moldlike filaments. The filaments have cellulose-based cell
walls, but no chitin as the walls of true fungi have.
• They produce flagellated gametes (sex cells) that
require an aquatic environment for dispersal.
• An example is the genus Phytophthora, the cause of
the potato blight that caused the Irish potato famine in
the 1840s.
New Classification based on
phylogeny: still being worked out.
Red Algae (Rhodophyta)
• 4,100 species
• Most abundant in tropical seas
• Can grow at great depths
– they have different pigments which can
use blue wavelengths (these are the
wavelengths that go deeper)
• Complex life cycles may include very
different forms
Alveolates
• Have tiny, membrane-bound sacs
(alveoli) underneath their outer
membranes
• Ciliates
• Sporozoans
• Dinoflagellates
Stramenopiles
• Unique trait is one of their two flagella
has thin filaments projecting from it
• Cells have four outer membranes
• Include
– Oomycotes
– Chrysophytes
– Brown algae