Download 5 BLY 122 Lecture Notes (O`Brien) 2010 II. Protists (Chapter 29) A

BLY 122 Lecture Notes (O’Brien) 2010
II.
Protists (Chapter 29)
A. Characteristics
1. Protists are all the eukaryotes that are not fungi, plants, or animals.
Picture Slide Fig 29.1
2. Protists are a PARAPHYLETIC group. (See Box 29.1, p. 594)
a. In paraphyletic groups, members share characteristics, but do not
necessarily share a common ancestor
b. Paraphyletic groups are not evolutionarily meaningful
3. Protists exhibit wide variation in morphology, size, and nutritional strategies.
Picture Slide: Fig. 29.8 The 8 major lineages of eukaryotes, most of which are protists.
4. All protists live in water, or moist soil, or interiors of other organisms.
B. Impacts on Human Health and Welfare
1. Many protists are important human pathogens
2. Malaria
a. World’s most chronic human health problem
b. About 1 million deaths per year (mostly infants & toddlers)
Picture Slide Fig 29.3 Plasmodium lives in mosquitoes and humans where it causes malaria.
Picture Slide: Distribution of the 2 most important species of human malaria
3. A trypanosome causes African sleeping sickness (ASS)
a. Endemic to central Africa
b. Kills humans, domestic cattle & domestic horses
Picture Slides (not in text) illustrating distribution of malaria and sleeping sickness as well as
18 century human travel in Africa
4. Effects of Malaria & ASS on African history
a. South Africa was isolated from the north (little north-south migration, trade, or
cultural interactions)
b. Inhibited European colonization (no large cities were established in central Africa)
C.
Evaluating Molecular Phylogenies
1. Molecular analysis of the gene encoding for rRNA in the small ribosome subunit
demonstrated that there are actually 8 major monophyletic eukaryotic groups
2. Thus, protists are paraphyletic, meaning that they are not all the descendants of a
single common ancestor
Picture Slide (Fig. 29.8) Identifying eight major lineages of eukaryotes
Picture Slide Baldauf, S.L., 2003, The Deep Roots of Eukaryotes Science, p. 1795 [Fig
posted with Chapter 28 notes]
D. What Themes Occur in the Diversification of Protists?
1.
The history of the Endosymbiosis Theory is an example of how evolutionary
science works
a. Scientific theories must make PREDICTIONS that can be TESTED
b. After numerous rejections, Lynn Margulis was able to publish her articulation of
the Endosymbiosis Theory in 1967
c. Her ideas were harshly criticized and originally were NOT accepted by
mainstream evolutionary biologists
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d. This changed in the 1980s when DNA sequencing data showed that eukaryotic
organelles had chromosomes that differed from nuclear genetic material as
Margulis had predicted
2. The Mitochondrion & Endosymbiosis Theory
a. Larger anaerobic eukaryotes engulfed aerobic prokaryotes, which became
endosymbionts that enabled the host cell to become aerobic.
Picture Slide: Fig. 29.11 Proposed Initial Steps in the Evolution of Mitochondrion by
Endosymbiosis
b. Evidence Supporting the Theory of Endosymbiosis
(1) Physical similarities exist between mitochondria, chloroplasts, and
prokaryotes.
(2) In addition, mitochondria…
(a) divide independently of the host cell.
(b) divide by fission as do bacteria
(c) have ribosomes similar to those in bacteria
Picture Slide: Fig. 29.16 Secondary endosymbiosis
3.
Secondary Endosymbiosis explains how chloroplasts, organelles with 4
membranes, could have originated in a similar way. (p. 609)
a.
A photosynthetic cyanobacterium was engulfed by a eukaryotic cell.
b.
The cyanobacterium provided the host with oxygen and glucose.
c.
The host cell provided protection for the endosymbiont.
4.
Mitochondria and chloroplasts have their own circular chromosomes that are
similar to bacterial chromosomes.
E. Morphological Diversity
1. The earliest eukaryotes solved the problem of increasing cell size.
a. Larger cells make possible the evolution of diverse structures and functions.
b. Compartmentalization into organelles increased the available surface area in
the interior of cells, facilitating food and waste transport in and out of the cell.
2. Organelles in single-celled protists perform same functions that are accomplished
by organ systems multi-celled eukaryotes
Picture Slide Fig 29.15 Protists have specialized intracellular structures.
3. Most protistans are unicellular, but some form colonies
Picture Slide of a colonial protistan (not in text)
F.
How do protests find food?
1. Ingestive feeding
a. Amebas engulf bacteria and other food materials with pseudopodia.
b. Ciliates sweep food into gullet-like cavities with currents generated by cilia
Picture Slides Fig 29.14a, b Pseudopodia and cilia capture food
2. Absorptive feeding
a.
Typical of parasitic protists
b.
Example: Plasmodium causes malaria
Picture Slide: Examples of absorptive feeding (not in text)
3. Photosynthesis
a. Vary in the types of photosynthetic pigments.
(1) Different groups of plants and algae utilize different wavelengths of light
(2) Water absorbs some wavelengths of light faster than others
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(3) Different alga groups are more efficient than others at absorbing light at
different depths
Picture Slide: Relative absorption of different wavelengths of light in seawater (not in text)
Picture Slide: Table 29.3
b.
Mutualistic symbiotic relationships involving photosynthetic protists are
common
Picture Slide 29.18:
G.
How do protests move?
1. Pseudopodia
2. Cilia
3. Flagella
Picture Slides Fig 29.19
H.
How do protests reproduce?
1. Sexual versus asexual reproduction
a. Meiosis introduces genetic variability through…
(1) crossover
(2) independent assortment
Picture Slides Fig. 12.7 (crossing over) and Fig. 12.9 (independent assortment)
b. Sexual reproduction requires fusion of haploid gametes from two parents
(1) The new zygote is genetically different from both parents
(2) Evolutionary significance: Increases likelihood that some offspring are
more resistant to environmental changes and pathogens than the parents.
2. Diversity in the timing of meiosis and sexual reproduction has led to a wide variety
of life cycles in the protists.
3. Remember:
a. Multi-celled organisms can be haploid
b. Mitosis can occur in haploid organisms
c. The life-cycles of some species alternate between multi-celled haploid and
diploid generations
Picture Slides Fig. 29.21a & b
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