Topic 2: Heterotrophic Protists Ch.
28
1. Autogeneous theory
• Organelles arose from the infolding of the
cell membrane which gradually became
elaborated into organelles.
• E.g. ER and nucleus.
Protist Diversity pp.575-579
• Protists are the earliest eukaryotic celled
organisms, and they are a very diverse group.
• Protists are polyphyletic meaning that they
are derived from two or more different
ancestors.
• Most are unicellular but some are multicellular.
• Some are photoautotrophs and others are
heterotrophs.
• In modern taxonomy the group is divided into
several kingdoms.
• There are two theories on how eukaryotic cell
developed from prokaryotic cells:
2. Endosymbiotic theory
- Prokaryotic organisms may have established a
symbiotic relationship within larger prokaryotic
cells.
- The smaller cells may have gained entry as
undigested prey or internal parasites.
- E.g. Mitochondria were once aerobic
heterotrophic prokaryotes.
• E.g. Chloroplasts were once photosynthetic
prokaryotes.
Fig. 25.9
Fig. 6.16
Protist Diversity
• Protists are larger than prokaryotics but not as
metaboliclly diverse.
E.g. Paramecium are free living heterotrophs.
E.g. Plasmodium are parasitic heterotrophs
which cause malaria. They spend part of their
life cycle in mosquitos and part in humans.
E.g. Euglena are free living mixotrophs with
chloroplasts.
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Protist Diversity
Fig. 28.10
• Zooprotists – Animal-like protists.
• Zooprotists are chemoheterotrophs and
contain the same organelles as animals and
may have cillia or flagella.
• They do not have chloroplasts nor cell
walls.
Kingdom Alveolata p. 582-585
Fig. 28.1
• Members have membrane bound sacs (alveoli)
just under cell membrane surface.
• Division Dinoflagellates – Photosynthetic.
• Division Apicomplexans - All are animal
parasites with complex life cycles of both sexual
and asexual stages requiring two or more
different host species. E.g. Plasmodium.
Fig. 28.9
Kingdom Alveolata
• Division Ciliophora – Have cilia for movement
and feeding.
• We will examine Paramecium caudatum as a
type example of ingestive heterotrophic protist
from division Ciliophora.
Fig. 28.11
2
Paramecium caudatum
• Large (150-300 μm) single celled freshwater
protists.
• Important structures include:
– Cilia – Movement.
– Oral groove – Where food enters.
– Gullet – Food enters here after leaving the
oral groove.
– Pellicle – A semi-rigid outer covering that
provides support.
– Contractile vacuole – Pumps water out of
the cell when it is in hypotonic solutions.
Paramecium caudatum
– Food vacuoles – Stores and digests food.
– Trichocysts – Spear-like defensive
structures.
– Macronucleus – Large nucleus which directs
cellular functions.
– Micronucleus – Smaller nucleus that is
involved in reproduction.
– Anal pore – Where waste leaves the cell.
Fig. 28.11
Paramecium Osmoregulation
• Due to freshwater environment and their semi
permeable membrane, water continually enters
hypertonic Paramecium.
• Osmoregulation is therefore, a major
concern.
• The contractile vacuole accumulate excess
water and expel to outside.
Paramecium Digestion
• Paramecium eat bacteria, algae and small
protozoans.
• Food enters the oral grove, through the gullet
and forms into a food vacuole.
• http://www.youtube.com/watch?v=a4aZE5FQ284
• Digestion occurs within food vacuoles due to
release of enzymes.
• Waste may diffuse through pellicle, pass
through anal pore or excreted by contractile
vacuoles.
Paramecium Gas Exchange
• Oxygen can diffuses into the cell and
carbon dioxide out directly through the cell
surface.
• http://www.youtube.com/watch?v=pahUt0RCKYc
• http://www.youtube.com/watch?v=iG6Dd3COug4
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Paramecium Reproduction
• Two important structures for reproduction are:
1. Micronucleus – Small nucleus that houses a
cell’s DNA and produces a macronucleus
during reproduction.
2. Macronucleus – Large nucleus that
regulates the non-reproductive functions of a
cell (I.e. metabolism).
Paramecium Asexual Reproduction
• Longitudinal binary fission – Asexual
reproduction in paramecium.
• This process involves the micronucleus and
organelles duplicating via mitosis.
• One cell splits to form two identical daughters.
• Macronucleus is then formed from
micronuclei.
• Process takes about 2 hours.
Fig. 28.11
.
Paramecium Conjugation
• Reproduction is usually asexual.
• Sometimes paramecium undergo conjugation.
• Conjugation – A sexual process in ciliates in
which two cells exchange haploid micronuclei.
Paramecium Conjugation
• Two genetically different diploid Paramecium
fuse at their plasma membranes.
• Micronucleus undergoes meiosis to produce
four haploid nuclei.
Fig. 28.11
Fig. 28.11
Paramecium Conjugation
Paramecium Conjugation
• Three micronuclei degrade.
• The remaining micronucleus divides by mitosis
to make two.
• Each Paramecium swap one micronuclei and
then separate from each other.
• Even though they are separated, both follow the
exact same reproductive process.
• The micronuclei then fuse (syngamy) to
become diploid again.
• Then it undergoes mitosis until eight nuclei are
produced.
Fig. 28.11
Fig. 28.11
4
Paramecium Conjugation
Paramecium Conjugation
• The macronucleus disintegrates and four of
the eight micronuclei differentiate into new
macronuclei.
• Each Paramecium now has four micronuclei
and four macronuclei.
• The Paramecium divides twice, producing
four daughters, each with one
macronucleus and one micronucleus.
• In total this process created eight new cells.
Fig. 28.11
Slime molds pp.594-596
Fig. 28.11
Slime Molds
Plasmodial Slime Molds
• Slime moulds are similar to fungi (produce
spores, are absorptive heterotrophs) but are
considered protists.
• There are two types: Plasmodial and Cellular.
Fig. 28.24
• They are basically one large cell. This results
in a low SA/V ratio.
• That is bad: internal transport is slow and it
decreases the effectiveness of the nucleus.
• To deal with these problems, the cytoplasm
flows in one direction and then the other
(cytoplasmic streaming) which distributes
nutrients and oxygen to the entire organism.
Fig. 28.25
5
Plasmodial Slime Molds
Fig. 28.24
- Also the cell contains many diploid nuclei to
keep cell operation functioning.
- In addition, plasmodial slime molds increase
their surface area by extending pseudopodia
(long thin projections) into food.
Cellular Slime Molds
• Cellular slime molds live as individual haploid
cells for most of their life cycle.
Sexual cycle:
• Sometimes, two haploid cells fuse to form a
large diploid zygote.
• The zygote undergoes meiosis then mitosis
to produce many individual halploid cells.
Cellular Slime Molds
Asexual Cycle
• When food in an area becomes low, individual
haploid cells aggregate into a mass called a
“slug.”
• The slug then moves to another area and forms
a “club-like” fruiting body.
Fig. 28.24
Cellular Slime Molds
Fig. 28.24
Fig. 28.24
• Cells on the inside of the fruiting body from
spores and are dispersed when the structure
breaks open.
• The cells on the outside of the fruiting body do
not reproduce. They sacrificed themselves for
the other individuals.
Fig. 28.24
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