Download 4 BLY 122 Lecture Notes (O`Brien) 2006 II. Protists (Chapter 28) A

BLY 122 Lecture Notes (O’Brien) 2006
II.
Protists (Chapter 28)
A. Characteristics
1. Protists are all the eukaryotes that are not fungi, plants, or animals.
Picture Slide Fig 28.7 Protists on the Tree of Life
2. Protists are a PARAPHYLETIC group. (See Box 28.1, p. 614)
a. Members share characteristics
b. Members of the group do not necessarily share a common ancestor
c. Not a meaningful evolutionary group
Picture Slide Baldauf, S.L., 2003, The Deep Roots of Eukaryotes Science, p. 1795 [Fig not
from your text]
3. Protists exhibit wide variation in morphology, size, and nutritional strategies.
Picture Slide: Fig. 28.7 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. 28.1. Protists particularly abundant in aquatic environments a. Plankton, b.
Kelp forests, c. Intertidal communities
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 28.2 “Yellow” malaria cells in red blood cells.
SIDETRACK: A Parasitologist’s Perspective on Intelligent Design, Material not in text.
C.
Evaluating Molecular Phylogenies
1. Molecular analysis of the gene encoding for rRNA in small subunit of ribosome
demonstrated that eight major eukaryotic groups were indeed monophyletic.
2. Protists are paraphyletic, meaning they do not comprise all the descendants of a single
common ancestor
Picture Slide (Fig. 28.7) is the current best estimate of eukaryotic evolutionary history.
D. Combining Data from Microscopy and Phylogenies: Understanding the Origin of
Mitochondria and Chloroplasts
1. The Endosymbiotic Theory of Lynn Margoilis
a. Larger anaerobic eukaryotes engulfed aerobic prokaryotes, which became
endosymbionts that enabled the host cell to become aerobic.
Picture Slide : Fig. 28.9 Proposed Initial Steps in the Evolution of Mitochondrion by
Endosymbiosis
b. Chloroplasts originated in a similar way.
(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.
Picture Slide: Fig. 28.18 Secondary endosymbiosis
2. Evidence Supporting the Theory of Endosymbiosis
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a.
Physical similarities exist between mitochondria, chloroplasts, and
prokaryotes.
b. In addition, mitochondria . . .
(1) are similar in size to most bacteria.
(2) divide independently of the host cell.
(3) divide by fission, as bacteria do.
(4) have ribosomes and synthesize proteins.
(5) have ribosomes of the same size as bacteria.
c. Mitochondria and chloroplasts have their own chromosomes, which are
circular and similar to bacterial chromomes.
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 28.12 Protists have specialized intracellular structures.
3. The evolution of multicellularity
a. Protistans may be unicellular, colonial, or multicellular.
Picture Slide Fig. 28.13 Examples
b. Multicellularity is generally defined by two criteria:
(1) When individual cells cannot survive independently
(2) The cells have differentiated so that different cells perform different
functions.
(a) Only a subset of the organism’s genes is expressed in a
differentiated cell.
(b) Different types of cells express different genes.
(3) Multicellularity is associated with specialization of cells, formation of
distinct tissue types, and larger overall size.
2. How do protests find food?
a. Ingestive feeding
(1) Amebas engulf bacteria and other food materials with pseudopodia.
(2) Ciliates: Sweep food into gullet-like cavities with currents generated by cilia
Picture Slides Fig 28.15.a, b Pseudopodia and cilia capture food
b. Absorptive feeding
(1) Typical of parasitic protests
(2) Amebic dysentery
Picture Slides Fig. 28.16, other amebic dysentery slide are not from text.
c. Photosynthesis
(1). Vary in the types of photosynthetic pigments.
(a) Different groups of plants and algae utilize different wavelengths
of light
(b) Water absorbs some wavelengths of light faster than others
(c) Different alga groups are more efficient than others at absorbing
light at different depths
Picture Slides: Fig 28.17
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(2) Mutualistic symbiotic relationships are common
Picture Slide 28.17d:
3. How do protests move?
a. Pseudopodia
b. Cilia
c. Flagella
Picture Slides Fig 28.20
4. How do protests reproduce?
a. Meiosis makes eukaryotic sexual reproduction possible.
(1). Meiosis reduces the diploid chromosome number to haploid and introduces
genetic variability through crossover and independent assortment.
(2). 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.
d. Diversity in the timing of meiosis and sexual reproduction has led to a wide
variety of life cycles in the protists.
Remember: 1. Multi-celled organisms can be haploid
2. Mitosis can occur in haploid organisms
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