Protists (Protistans) and Life cycles

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Protists (Protistans) and Life cycles
Protists are generally unicellular, but sometimes
multicellular species.
Most live in water, or places that have a watery
film.
Protists are all eukaryotic, their DNA is
enclosed in a nucleus inside the cell unlike
bacteria, which, whilst unicellular, are
prokaryotic and have no nucleus to enclose their
DNA.
Some protists are heterotrophs, some are
autotrophs and a few species are both!
Protists are usually grouped into three
subcategories plant-like protists, animal-like
protists , and fungus-like protists.
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A Basic Life Cycle Structure
HAPLOID
DIPLOID
Is this what humans do?
No, I dont think so.
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Plant-like Protists (Algae) 6 phyla s
Plant-like Protists (Algae) 6 phyla
1. Euglenas (Euglenophyta)
Some are autotrophs when sunny and heterotrophs
when dark. Unicellular, found mostly in fresh
water. Some have a flagella
2. Diatoms (Chrysophyta)
Examples in the lab. Fig 23.16c in text book
Diatoms make 20 to 25 of global organic carbon
fixation.
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3. Dinoflagellates (Pyrrophyta)
Ocean dwelling, unicellular, covered by stiff
plates, two flagella, bioluminescent
(biochemical reaction to oxygen). Fig 23.17 of
text book.
4. Green Algae (Chlorophyta)
Mostly unicellular, but some form colonies, and a
few are multicellular. Live in fresh water,
salt water, and a few live on land. Fig 23.21 of
text book
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Chlamydomonas
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Life cycle of Chlamydomonas
Diploid Stage
Nuclear Fusion
Meiosis and Germination
Haploid Stage
Haploid cell (- strain)
Haploid cell ( strain)
Mitosis occurs. Whether the resulting cells
develop into spores or gametes depends on
environmental conditions.
SEXUAL REPRODUCTION Mainly when nitrogen levels
are low and light is of a certain quality and
intensity, the cells develop into gametes.
Cytoplasmic Fusion
ASEXUAL REPRODUCTION
isogamy
Page 389 Fig 23.22
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What is different about the Chlamydomonas life
cycle compared to the basic life cycle?
One difference
two important features
and
Prizes!
Prizes!
Prizes!
Prizes!
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Important life cycle features of Chlamydomonas
Sexual reproduction induced by environmental
conditions
and - gametes look the same
In Chlamydomonas the diploid phase is a resting
stage no mitosis of the diploid phase
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The life cycle of Ulva
How does this suit Ulvas niche?
Important Feature
Both the spores and the zygote develop into a
multicellular thallus
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Whats the function of sexual reproduction?
Sexual reproduction introduces variations in the
details of traits among offspring.
This variation is the FEEDSTOCK of natural
selection

• Differentiation of the sexes is a characteristic
  that enables specialization in
• Ensuring fertilization
• (b) Producing and distributing successful progeny

In some plant types producing and distributing
large numbers is achieved by spores
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Alternation of Generations
The occurrence within the life cycle of an
organism of two or more distinct forms
(generations), which differ from each other in
appearance, habit, and method of reproduction.
The phenomenon occurs in some protists, certain
lower animals (e.g. parasitic flatworms), and in
plants.
The malaria parasite (Plasmodium), for example,
has a complex life cycle involving the
alternation of sexually and asexually reproducing
generations.
 In plants the generation with sexual
reproduction is called the gametophyte and the
asexual generation is the sporophyte, either of
which may dominate the life cycle, and there is
also alternation of the haploid and diploid
states.
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The pigment phycoerythrin reflects red light and
absorbs blue. Blue light penetrates water to a
greater depth than light of longer wavelengths
and so these pigments allow red algae to
photosynthesize and live at somewhat greater
depths than most other "algae". Fig 23.18 of
text book.
6. Brown Algae (Phaeophyta)
Large leaf-like structures called blades and
frequently air-filled sacs called air bladders
and root-like structure called a holdfast. Not
closely related to land plants. Cells contain
pigments such as chlorophyll c and fucoxanthin.
They also lack plasmodesmata and starch
production. Fig 23.20 of text book.
Alginic acid used in toothpastes, soaps, ice
cream, tinned meats, fabric printing. It forms a
stable viscous gel in water, and is as a binder,
stabilizer, emulsifier, or moulding agent.
Ascophyllum nodosum
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Life cycle of Porphyra
How does this life cycle differ from that of Ulva?
sporophyte (2n)
zygote
Diploid Stage
Fertilization
Meiosis
Haploid Stage
germinating spore (n)
male gametes
female gametes
gametophyte (n)
Fig 23.19 Page 386
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Animal-like Protists
1. Sarcodines (Sarcodina)
Food is surrounded by pseudopods and stored in a
food vacuole
2. Flagellates (Mastigophora)
Parasite causing gasteroenteritis. Giardia
lamblia trophozoites, are released from cysts by
contact with stomach acids and attach to the
epithelium of the small intestine. Scanning
electron microscope photograph. 
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These protists move by beating cilia that also
help it capture food. Paramecium is an example
Named for a complex of organelles located at the
apex of the cell used to break through tissues
and cells of the host. Sexual and asexual stages
and often need two or more hosts to complete life
cycle.
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Fungus-like Protists
Saprophytes and parasites.
"Oomycota" means "egg fungi," and refers to the
large round oogonia, or structures containing the
female gametes, (picture)
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Slime moulds have structural adaptations
Slime moulds have structural adaptations and life
cycles that enhance their ecological role as
decomposers
2 - Plasmodial slime moulds or true slime moulds,
are a large single-celled mass with thousands of
nuclei called a plasmodium formed when individual
flagellated cells swarm together and fuse into
one large bag of cytoplasm with many diploid
nuclei.
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Characteristics of Dictyostelium
3 - Cellular slime moulds spend most of their
lives as separate single-celled amoeboid
protists, but upon the release of a chemical
signal, individual cells aggregate into a great
swarm, known as a pseudoplasmodia and eventually
muticellular slugs.
Up to 100,000 cells signal each other by
releasing a chemo-attractant and aggregate to
form a mound.
Subsequent processes depend on cell-cell
communication
Many molecular and cellular processes of
communication appear to have remained unchanged
throughout evolution.
A model organism for bio-medical research.
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The life cycle of a cellular slime mold,
Dictyostelium
1 Stalked, spore-producing structure releases
spores.
MITOTIC CELL DIVISION
2 Spores give rise to free-living amoebas that
feed, grow, and reproduce by mitotic cell
division.
MATURE FRUITING BODY
AGGREGATION
CULMINATION
But whats wrong with this life cycle?
3 When food gets scarce, the amoebas stream
together to form an aggregate that crawls like a
slug.
4 The slug may start developing at once into a
spore-bearing structure, or it may migrate
elsewhere first.
either
or
MIGRATING SLUG STAGE
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Fig. 23.3, p. 375
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Protists are not plants but they follow the
same 5 principles in their own ways
Plants accumulate matter and make growth
Plant growth is an organized process following rules of anatomy, morphology and physiology
Plants actively maintain their heat and water balance
Plants have a life cycle with reproduction and dispersal
Evolution is a constant process
For unicellular organisms growth (cell division)
? asexual reproduction
Many protists show distinctive physiological
adaptations though some have distinct morphology
Life cycles are adapted to suit ecological
conditions
Many protists are specialists adapted to very
distinctive environments