protists. what is a protist? a protist is any organism that is not a plant, an animal, a fungus, or...
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Protists
What is a Protist?
A protist is any organism that is not a plant, an animal, a fungus, or a prokaryote. The 1st eukaryotic organisms on Earth,
appearing nearly 1.5 billion years ago, were protists.
Protists are a diverse group that may include more than 200,000 species.
Most protists are unicellular, aquatic organisms, including both freshwater and marine species.
Protists can reproduce sexually or asexually, depending on the species.
A Sample of Protistan Diversity
Most protists are classified by their method of obtaining nutrients: Animal-like protists
are heterotrophs – absorb or ingest food Plant-like protists
Photosynthesize – contain chloroplasts for photosynthesis Fungus-like protists
are parasites or decomposers
The 4 phyla of animal-like protists (called PROTOZOA) are distinguished from one another by their means of movement:
1. Zooflagellates swim with flagella2. Sarcodines move by extensions of cytoplasm3. Ciliates move by means of cilia4. Sporozoans do not move on their own
The Protozoans: Animal-Like Protists
Zooflagellates
Animal-like protists that swim using flagella are referred to as zooflagellates.
Most have either 1 or 2 flagella (although some species have many).
Absorb food through their cell membranes Most live in lakes and streams, although some live in
the bodies of other organisms Most reproduce asexually by means of binary fission,
although some have a sexual life cycle
Sarcodines
Sarcodines are animal-like protists that use pseudopods for feeding and movement. Pseudopods (false feet)
are temporary projections of cytoplasm.
The best known sarcodines are amoebas. Amoeboid movement
involves the cytoplasm of the cell streaming into the pseudopod allowing the rest of the cell to follow.
CiliatesAnimal-like protists
that move and feed by means of cilia are known as ciliates. Cilia are hair-like
projections similar to flagella.
Most ciliates are free living (non parasitic).
Some of the best known ciliates belong to the genus Paramecium.
Sporozoans
Members of the group Sporozoa are animal-like protists that do not move on their own and are parasitic.
The sporozoan Plasmodium, which causes malaria, is carried by the female Anapheles mosquito.
As many as 2 million people die from malaria each year.
Other diseases caused by animal-like protists include:
African Sleeping Sickness – trypanosoma parasite is transmitted by tsetse fly.
Giardia - diarrheal illness caused by a microscopic parasite, Giardia intestinalis – a sporozoan.
Figure 28.11
Inside mosquito Inside human
Sporozoites(n)
Oocyst
MEIOSIS
Liver
Liver cell
Merozoite(n)
Red bloodcells
Gametocytes(n)
FERTILIZATION
Gametes
Zygote(2n)
Key
Haploid (n)Diploid (2n)
Merozoite
Red blood cell
Apex
0.5 µm
Life Cycle of Plasmodium
An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva.
1 The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells (see TEM below).
2
The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect new red blood cells.
3
Some merozoites form gametocytes.4
Another Anopheles mosquitobites the infected person and picksup Plasmodium gametocytes alongwith blood.
5 Gametes form from gametocytes.Fertilization occurs in the mosquito’sdigestive tract, and a zygote forms.The zygote is the only diploid stagein the life cycle.
6
An oocyst developsfrom the zygote in the wall of the mosquito’s gut. Theoocyst releases thousands
of sporozoites, whichmigrate to the mosquito’s
salivary gland.
7
Ecology of Animal Like Protists
Not so Good: Can be parasitic/cause disease Malaria, African Sleeping Sickness, Cryptosporidium
Good: Symbiosis Termites have beneficial animal-like protists called
Trichonympha in their stomachs Break down cellulose in wood so termites can use it as
food
Main Characteristic: Chlorophyll Green pigment that traps light, carries out
photosynthesis Evolved from symbiosis of photosynthetic bacteria and
larger, heterotrophic bacteria
Plant-like protists are commonly called “Algae”
Can contain cell wall like plants Unicellular (4 types)
Euglenophytes, Dinoflagellates, Chrysophytes, Diatoms
Multi-cellular (3 types) Red Algae, Brown Algae, Green Algae
Plant-Like Protists
The 4 phyla of plant-like protists that are grouped together as unicellular algae are:
1. Euglenophytes2. Dinoflagellates3. Chrysophytes4. Bacillariophytes
Unicellular Algae
Euglenophytes
Algal Blooms
DinoflagellatesDinoflagellates are plant-like organisms that can
be photosynthetic or heterotrophic. Abundant components of both marine and freshwater
phytoplankton Many species are luminescent.
Red TidesGreat blooms of
the dinoflagellates have occurred in recent years on the east coast. These blooms are
known as “red tides”. These species release
a potentially harmful toxin that infect certain shellfish.
Eating these infected shellfish can be harmful or fatal.
Dinoflagellates & Bioluminescence
Chrysophytes
Members of the phylum Chrysophyta are a diverse group of plantlike protists that have gold-colored chloroplasts.
includes yellow-green algae and golden-brown algae reproduction can be sexual or asexual
Diatoms
Diatoms are plant-like protists that produce thin, delicate cell walls rich in silicon (the main ingredient in glass). Diatoms are among the most abundant organisms on
Earth! Diatoms are beautiful!
Ecology of Plant-Like Protists
Most unicellular species beneficialAct as producers in the marine food chain
Form Phytoplankton for consumer organisms to eat Approx. ½ of the photosynthesis on earth!!!
Produce large amount of oxygen
Symbiosis: Coral Reefs, Clams Provide food via photosynthesis, receive a home
The 3 phyla of algae that are largely multicellular are commonly known as: red algae brown algae green algae
A major difference among these phyla are their photosynthetic pigments.
Multicellular Algae
Red Algae
(a) Bonnemaisonia hamifera. This red alga has a filamentous form.
Dulse (Palmaria palmata). This edible species has a “leafy” form.
(b)
A coralline alga. The cell walls ofcoralline algae are hardened by calcium carbonate. Some coralline algae aremembers of the biological communities around coral reefs.
(c)
Brown Algae
Giant kelp
Green Algae
Chlamhydomonas
unicellular
green algae
Volvox
colonial
green algaeUlva
multicellular
green algae
Spirogyra
Multicellular green algae
Food for humans Food for invertebrates and fishes in mariculture Animal feed Soil fertilizers and conditioners in agriculture Treatment of waste water Diatomaceous earth (= diatoms) Chalk deposits Phycocolloids (agar, carrageenan from red algae;
alginates from brown algae) Drugs Model system for research Phycobiliproteins for fluorescence microscopy
Beneficial Aspects of Algae
Blooms of freshwater algaeRed tides and marine bloomsToxins accumulated in food chainsDamage to cave paintings, frescoes, and other
works of artFouling of ships and other submerged surfacesFouling of the shells of commercially important
bivalves
Detrimental Aspects of Algae
Fungus-Like Protists
Fungus-like protists are heterotrophs that absorb nutrients from dead or decaying organic matter. Unlike true fungi, however, funguslike protists
have centrioles and lack chitin in their cell wall.The fungus-like protists include:
Cellular slime molds Acellular slime molds Water molds
Slime Molds
Slime molds are fungus-like protists that play key roles in recycling organic material. They are found in damp places that are rich in organic
matter, such as forest floors.
The 2 groups of slime molds are: Cellular slime molds: individual cells remain distinct –
BUT – when food becomes scarce, cells join with others to reproduce in a multicellular unit with a distinct cell membrane
Acellular (Plasmodial) slime molds: cells fuse to form larger cells called plasmodium during some life cycle phases – this is the feeding stage of the organism
CELLULAR SLIME MOLDS
ACELLULAR SLIME MOLDS
Cellular v/s Acellular Slime Molds
What is the difference between the large slug-like colony formed by cellular slime molds and the plamodium formed by acellular slime molds? The slug-like colony is a mass of cells that is
multicellular (made up of many individual cells) EACH WITH A DISTINCT CELL MEMBRANE.
The plamodium is a mass of cytoplasm that contains many nuclei but NO CELL WALLS OR MEMBRANES
Oomycetes (Water Molds and Their Relatives)
Oomycetes Include water molds, white rusts,
and downy mildews Were once considered fungi based
on morphological studiesMost oomycetes
Are decomposers or parasites Have filaments (hyphae) that
facilitate nutrient uptake
Ecology of Fungus-Like Protists
The ecological impact of oomycetes can be significant Phytophthora infestans causes late blight of
potatoes – Irish Potato Famine Overgrowth of water mold caused by wet and cool
conditionsSlime molds and water molds are the MOST
important recyclers of organic materialWhy is the earth not littered with dead
organisms? Tissues broken down by Fungi Like Protists and
other decomposers