Download 5 BLY 122 Lecture Notes (O`Brien) 2009 II. Protists

BLY 122 Lecture Notes (O’Brien) 2009
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.
Picture Slide: Fig. 29.2. Protists particularly abundant in aquatic environments
a. Open ocean plankton
b. Shallow coastal water kelp forests
c. Intertidal habitats
B. Impacts on Human Health and Welfare
1. Many protists are responsible for human diseases
2. Malaria
a. World’s most chronic human health problem
b. About 1 million deaths per year (mostly pre-schoolers)
Picture Slide Fig 29.3 Plasmodium lives in mosquitoes and humans where it causes malaria.
c. Recent research showing disease’s complexity
Recent research: “Malaria infection increases attractiveness of humans to mosquitoes” From
PLoS Biology, 2005, 3(9) p. 1590-93
(1) Experiment 1
(a) Scientists compared the biting rates of Anopheles mosquitoes on 3 groups
of children
i No malaria
ii Malaria, but no stages that infect mosquitoes
iii Malaria, with infective stages
Picture Slide showing experimental set-up
(b) Results: Infective children (with gametocytes) attracted 2X as many
mosquitoes as the 2 other groups
Picture Slide showing results
(2) Experiment 2
(a) Cured parasitized children and repeated the experiment
(b) Results: Children whose blood was cleared of infective stages no longer
attracted mosquitoes
(c) Conclusion: Infective stages of malaria somehow attract mosquitoes
(probably an odor)
Picture Slide showing results
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
5
2. Thus, protists are paraphyletic, which means 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 not
from your text]
D. What Themes Occur in the Diversification of Protists?
1. 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
Picture Slide: Fig. 29.16 Secondary endosymbiosis
b. Evidence Supporting the Theory of Endosymbiosis
(1) Physical similarities exist between mitochondria, chloroplasts, and
prokaryotes.
(2) In addition, mitochondria . . .
(a) are similar in size to most bacteria.
(b) divide independently of the host cell.
(c) divide by fission, as bacteria do.
(d) have ribosomes and synthesize proteins.
(e) have ribosomes of the same size as bacteria.
2.
Secondary Endosymbiosis explains how chloroplasts, organelles with 4
membranes, could have originated in a similar way. (p. 609)
(1)
A photosynthetic cyanobacterium was engulfed by a eukaryotic cell.
(2)
The cyanobacterium provided the host with oxygen and glucose.
(3) The host cell provided protection for the endosymbiont.
3.
Mitochondria and chloroplasts have their own chromosomes, which are circular
and 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. Protistans may be unicellular, colonial, or multicellular.
Picture Slide Examples (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)
6
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
(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 makes eukaryotic sexual reproduction possible.
b. Meiosis reduces the diploid chromosome number to haploid and introduces
genetic variability through crossover and independent assortment.
c. Fusion of haploid gametes from two parents creates genetically different
offspring, some of which may be more resistant to environmental changes
and pathogens than the parents.
2. Variation in life-cycles
a. 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 29.21a & b
7