BLG 144 CHP 29 PROTISTS
Multicellularity:
exclusive to domain eukarya -multiple origins in many lineages..
4. Rhizaria
single celled amoeba with no cell walls but some produce shells -long slender pseudopodia (not lobe like) -Obtained chloroplast via secondary endosymbiosis
spores
single cells- not gametes. develop into adult organism..
alternations of generation:
sporophytes (2n) -->spores (n)-->gametophytes (n) --> gametes (n)--> zygotes (2n) (REPEAT) -SPOROPHYTES PRODUCE SPORES BY MEIOSIS, GAMETOPHYTES PRODUCE GAMETES BY MITOSIS
7. Opisthokonta
unikonta that lack cell walls (along with amoebozoa) -gave rise to colonial and multicellular fungi and animals.
protist nutrition: 2. ABSORPTION
*MOST COMMON* Nutrients taken up directly across plasma membrane from environment. -USED BY DECOMPOSERS AND PARASITES. live inside hosts since some dont have a mitochondria.
1. Amoebozoa
-UNIKONTA -lack cell walls -pseudopodia for ingestion and movement -also include lobose amoeba -slime moulds (individual single cells with many diploid nuclei)
What is another variation in the reproductive cycle?
-alternation of generations- multicellular forms of both haploid/diploid states. -may look identical or different. -evolve independently in various groups.
Life cycle of protists:
-can be haploid dominant or diploid dominant -meiosis and mitosis phases.
5. Alveolata
-clade: chromoalveolata (within bikonta) -members with small sacs (alveola) -most are unicellular -cilliates/dinoflagellates
What other factor drove speciation in protists?
-diversification in pigments and less competition -can absorb many wavelengths of light.. *KEEP IN MIND THAT NOT ALL PROTISTS CAN PHOTOSYNTHESIZE, SOME OF THEM LOST CHLOROPLASTS OR THE CHLOROPLASTS CHANGED FUNCTION*
protist nutrition: 3. photosynthesis: origin of chloroplast
-endosymbiotic theory states that eukaryotic chloroplast originated when a protist engulfed a cyanobacterium. Once inside a protist, photosynthetic bacterium provided host with oxygen and glucose in exchange for protection/access to light.
protist nutrition: 1. INGESTION
-engulfment of food by protists with no cell wall -use pseudopodia and have flexible cytoskeleton -can use cilia to direct food into mouth
2. Excavata
-feeding groove -all lack mitochondria (likely lost or greatly reduced) -parasitic species
Mitochondrion origins: ENDOSYMBIOTIC THEORY
-generate ATP by using pyruvate as electron donor& oxygen as acceptor. -endosymbiotic theory: mitochondria originated when a bacterial cell took up residence inside a eukaryote billions of yrs ago. early eukaryotes were only capable of anaerobic fermentation.
6. Stramenophiles
-heterokonta -distinguishing feature: hairy flagella -clade chromoalveolata -water moulds, diatom and brown algae
support and protective structures (cytoskeleton):
-little variation in basic cytoskeleton structure, more diversity in other structures for support/protection. -CELL WALLS MADE OF SILICON, DIOXIDE, CELLULOSE AND SHELLS MADE OF CALCIUM CARBONATE. also *synapomorphies that rep different monophyletic groups*
How do protists move?
-motility is important for predatory and autotroph protists 1. amoeboid swimming: extensions of cytoplasm form pseudopodia. disassemble and reassemble cytoskeleton with ATP. 2. Swimming via beating cilia or whip like flagella. closely related protists can have different means of locomotion.
Why was this selected for by natural selection?
-mutually beneficial: host supplied bacterium with protection and carbon compounds while bacterium produced much more ATP than host cell could synthesize. cells can produce MORE ATP.
How do protists reproduce?
-no SEXUAL REPRODUCTION BEFORE PROTISTS. -asexual reproduction via mitosis in eukaryotes. genetically identical offspring -sexual reproduction via cell meiosis -BOTH REPRODUCTIVE MODES IN PROTISTS. usually asexual unless triggered (ex. crowding, season, food scarcity)
what is a protist?
-not land plants, fungi or animals. -not one monophyletic group but a paraphyletic group. (no synapomorphies).
protist nutrition: 3. photosynthesis: primary endosymbiosis
-primary endosymbiosis: cyanobacteria evolved into plastids (double membrane) and gave rise to red/green algae. -algae plastid DNA is similar to cyanobacteria DNA.
Evidence for endosymbiosis theory (similarities between bacteria and mitochondria)
-proteobacteria groups only found in eukaryote cells. -similar proteobacteria/mitochondrion size -mitochondria and bacteria replicate via fission -mitochondrial ribosomes manufacture proteins -double membrane -mitochondria have their own genome (circular molecules like bacteria) -phylogeny of mitochondrial DNA is much closer to proteobacteria than eukaryotes.
protist nutrition: 3. photosynthesis: secondary endosymbiosis
-red and green algae underwent secondary endosymbiosis. They were ingested by predatory protists and became endosymbionts themselves. 4 MEMBRANES IN TOTAL. -This engulfed algae still carries out photosynthesis with its plastids. -vestigial nucleus -chlorarachniophyte plastid structure
How do biologists study protists?
-rely on morphological traits. 7 major groups based on cell morphology. -SYNAPOMORPHIES REFLECT MAJOR CHANGES IN CELL PROTECTION, SUPPORT, MOVEMENT AND FEEDING..combined with genetic sequencing
Why are nuclear envelopes advantageous?
-seperates genome transcription and translation -novel way to control gene expression. further diversification after evolution of nucleus. distinctive structure of nucleus is a SYNAPOMORPHY that allows us to recognize lineages.
how many key protist lineages are there? how are they distinguished?
-there are 7 (ALL IN DOMAIN EUKARYA) -based on DNA and morphology -multiple independent events for diversification (multicellularity, photosynthesis, parasitism)
Why do biologists study protists?
1. health: various pathogenic protists ex. malaria causing protozoan (plasmodium) ex2: crop failure: irish potato famine from p.infestans (fungus like protist) that infested potato tubers. ex. 3: harmful algae blooms: rapid population growth..some produce toxins particularly Dinoflagellates..build up in filter feeding organisms.
some general characteristics of protists?
1. more structural/functional diversity 2. often unicellular (some are colonial/multicellular) 3. photoautotrophs (chloroplasts), heterotrophs, mixotrophs. (varies by lineage) 4. photosynthetic (algae), ingestive/animal like (protozoan), fungus like.
what are some distinguishing traits in eukaryotes?
1. nuclear envelope 2. larger and more complex, cytoskeleton 3. many are multicellular 4. reproduce asexually through mitosis or sexually via meiosis.
what are the 3 major monophyletic eukaryotic lineages? *table 29.2*
1. unikonta (amoebozoa/opisthokonta) includes fungi/animals. 2. bikonta (chromalveolata: smaller monophyletic lineage within bikonta)
Why do biologists study protists? cont'd
2. ecological importance: critical components of food chains&webs. -primary producers (photosynthetic protists) ultimate source of energy for all other consumers.
Nuclear envelope origins: hypothesis/support
Infolding hypothesis states origin of nuclear envelope is based on infoldings of the plasma membrane. Gives rise to nuclear envelope and ER together. SUPPORT FOR THIS HYPOTHESIS: infolding of plasma membrane occur in bacteria found today and the nuclear envelope and ER of todays eukaryote are continuous.
3. Plantae
green or red algae (unicellular or colonial). land plants -distinguishing feature: chloroplast
-key differences between haploid/diploid dominant life cycles:
haploid dominance: -meiosis occurs in zygote. -gametes and mature cell are haploid diploid dominance: meiosis occurs in adult cell. -only gametes are haploid
what morphological innovations evolved in protists?
living eukaryotes have features that prokaryotes lack. these features evolved independently: 1. nucleus/endomembrane system (nuclear envelope) 2. mitochondria 3.cytoskeleton 4. flagella that undulate
sporophyte
multicellular diploid form (cells produce haploid spores via meiosis)
gametophyte
multicellular haploid form (produce gametes via mitosis)