Early Life Forms Flashcards
What were the characteristics of LUCA (Last Universal Common Ancestor)?
Anaerobic CO2 fixing H2 dependent N2 fixing Thermophilic Radical reaction mechanisms
What environment did LUCA inhabit?
Geochemically active
Rich in H2
Rich in CO2
Rich in iron
What was the name of the last supercontinent?
When did it split?
Pangaea
175 million years ago
What life form was the first photosynthesiser?
Cyanobacteria
What light blue pigment does cyanobacteria produce, that helps to distinguish them from algae?
Phycocyanin
What do cyanobacteria possess to fix nitrogen when supply becomes limited?
Heterocytes
What is the property nitrogen-fixing cells must have and why?
Thicker cell walls
Because the enzyme nitrogenase involved in fixing nitrogen is sensitive to the presence of oxygen, and the thicker cell wall slows down the diffusion of oxygen into the cell so nitrogen can still be fixed effectively
What are the non-nitrogen-fixing cells called, and what are they specialised to do?
Vegetative cells
They can rapidly make small gas vesicles filled with air, giving the cyanobacteria buoyancy to float up to the surface and photosynthesise. They can also reverse this process
What overwintering structures can cyanobacteria produce?
Akinetes
They remain when others break down, and can survive in extreme conditions such as high temperature / pH, or lack of oxygen
What problems can cyanobacteria cause to drinking water?
Cyanobacteria can enter a planktonic state and produce chemicals that cause tastes and odours in drinking water.
It is expensive to remove them as they form biofilms at the bottom of reservoirs rather than floating.
The tastes and odours are caused by metabolites such as geosmin and 2-MIB.
Benthic cyanobacteria may also be responsible for these outbreaks
What is primary symbiosis?
The engulfment of a cell by another free living organism and retains some of its characteristics
What is secondary symbiosis?
When a eukaryote cell engulfs another cell that has undergone primary symbiosis already
Primary symbiosis gave rise to which types of algae?
Red and green algae
What are dinoflagellates and where are they found?
Autotrophic (self-feeding) components of the phytoplankton community
Major component of marine phytoplankton, but also found in freshwater
Why do dinoflagellates have spines?
To give them an elaborate form, enabling them to stay under the water column and deterring predators
What are the two halves of a dinoflagellate called?
Upper half: epicone
Bottom half: hypocone
What are the two flagella that each dinoflagellate possesses and why do they have them?
The transverse undulipodia (emerges from the transverse groove) which enables dinoflagellate to swim in a spiral pattern
The longitudinal undulipodia which acts like a rudder to control movement
What are dinoflagellates encased in?
The amphiesma, which consists of flattened vesicles called thecal plates (complex cellulose plates)
How do dinoflagellates obtain energy?
Some are photosynthetic, some are heterotrophs and some are mixotrophs
What taxonomic grouping is a dinoflagellate?
Phylum
What taxonomic grouping is a diatom and what is the next highest grouping above it?
Class
Phylum: Ochrophyta
What can toxic dinoflagellates do?
Kill fish in the ocean
What is the equation for bioluminescence in dinoflagellates?
Luciferin + O2 —(luciferase)—> (P)* —> P + hv
Excited electrons emit light
Warns predators not to eat them
What can dinoflagellates retain from engulfed algae?
Chloroplasts which they can use to photosynthesise
What is a diatom?
Photosynthetic protist which is a major component of marine phytoplankton
What is the hallmark of diatoms?
Silica cell wall of two halves: epitheca and hypotheca
Many complex patterns
What are the two basic forms of diatom?
Centric (radially symmetrical)
Pennate (bilaterally symmetrical)
What forms to diatoms come in?
Planktonic forms (just drift/float) Motile forms (glide by means of extruded mucilage, a sticky substance produced by nearly all plants and some microorganisms) Colonial formations (aids floatation)
How much of the world’s oxygen do diatoms produce?
1/4
Up to how much carbon do diatoms fix in oceans?
40%
Why is it useful that diatom’s silica shells preserve well?
They are an indicator of past climate
What environment does green algae inhabit?
Mainly freshwater but also shallow marine areas
What forms does green algae live in?
Unicellular
Filamentous (in the form of long rods)
Colonial (lots of cells in close association)
Multicellular (each cell could not survive alone unlike in a colony)
What pigments give green algae their bright green colour?
Chlorophyll a and b
What structure is starch stored around in a green algal cell?
Pyrenoid (found inside the chloroplast)
Name 2 examples of unicellular green algae
Chlamydomonas
Chlorella
On which green algae genus were the first precise measurements of the action of photosynthesis taken and in what year?
Chlorella
1943
How do green algae prevent damage from high irradiance and UV?
Develop brownish-purple accessory pigments in vesicles
What are the two types of colonial forms?
Motile (cells adhere loosely)
Non-motile (lose flagella and float with current)
What is a coenocytic organism?
An organism with multiple nuclei but enclosed by only one cell wall, so the cytoplasm of each cell is continuous)
How do coenocytic forms of filamentous green algae form?
If karyokinesis (division of a cell nucleus during mitosis) occurs without cytokinesis
What does parenchymatous mean?
A three-dimensional body in which the cells are connected by plasmodesmata (microscopic channels which transverse cell walls)
This makes algal forms look like plants
What is an example of one of the most advanced algae that looks superficially like a higher plant and what are it’s reproductive structures?
Chara
It has advanced reproductive structures called oospores with protective cells
What is an oospore?
A thick-walled zygote
What are the properties of Euglenids?
Mostly freshwater
Flagella arise from depression at the apex
Large contractile vacuole
Eyespot
Flexible body
One species overwinters in the hindgut of a damselfly and loses it’s eyespot
What are common genera of Euglenids (class)
Euglena
Trachelomonas
What are haptonema? What group are they unique to?
Peg-like organelles attached near the flagellum and unique to the group Haptophycae
What are haptophycae?
Uninucleate flagellates (organisms which possess flagella at some point in their life cycle) with haptonema
What is a macrophyte?
An aquatic plant large enough to be seen by the naked eye
What is the form that red algae species usually exist as?
Multicellular organisms with filamentous and membranous forms, but cells are joined by nothing more than mucilage
What are the purposes of haptonema?
Feeding, avoidance or attachment
What is the other name for brown algae?
Phaeophyta
What is the other name for green algae?
Chlorophyta
Where is brown algae found?
Almost exclusively marine, prefers cold, turbulent waters
Many intertidal species
Which type of algae are kelps?
Brown algae / Phaeophyta
What is are fucoids (order) and where are they found?
Vegetative growth (reproduction by asexual means) Found on intertidal rocky shores
What type of branching does a fucoid show?
Dichotomous branching (equal division of a terminal bid into two equal branches)
What sex is a fucoid?
Hermaphrodite (has both male and female sex organs)
What are receptacles and conceptacles and what type of algae possesses them?
Receptacles are a hollow object used to contain something
Conceptacles in the receptacles contain reproductive structures
They are possessed by fucoids (brown algae)
What type of gametes are released from fucoid receptacles in summer?
Motile gametes
What pigments mask the chlorophyll a pigments giving brown algae it’s colour?
Fucoxanthin
Tannin
(Laminarin)
What are Laminarians (genus)
Parenchymatous seaweeds that have a meristem between the stipe and blade
What is a meristem?
A tissue in plants made up of dividing cells, where growth can take place
Where are Laminarians found?
In colder waters
Why might Laminarians be affected by global warming?
Gametophytes typically fail to produce gametes at higher temperatures
Describe the morphology of Laminarians
Trumpet hyphae (conducting cells called sieve cells) which are part of central medulla tissue
Each sieve cell separated by sieve plates with pores in them (may have evolved from plasmodesmata)
Photosynthetic produce actively transported through the algae
What two forms do algae alternate between?
Diploid sporophyte and haploid gametophyte
What causes the end of periods of abundance of kelp?
Sea urchins enter the area and weigh down the kelp so it can’t photosynthesise, These periods are called “urchin barrens”
What is a holobiont? What type of algae are holobionts?
A host with many microbial symbionts. Seaweeds are holobionts
What properties do the bacteria living on seaweeds have?
Antifouling properties (they form a film over the seaweed and prevent other microorganisms from growing there)
What is another name for red algae?
Rhodophyta
What are the properties of Rhodophyta (red algae)
Lack flagella
Store floridian starch (the primary sink for fixed carbon from photosynthesis)
Contain phycobiliprotein pigments
Unstacked thylakoids
Chloroplasts lack endoplasmic reticulum
Can form crusts - much smaller than brown algae
Many have calcium carbonate in cell walls
What are phycobiliprotein pigments?
Retained from cyanobacteria ancestor, used to capture light that can be passed to chlorophyll
Where are red algae (Rhodophyta) most commonly found?
Mainly marine, bloom in spring tides
What type of algae can grow in areas with high CO2 concentration and even in sewage?
Seaweeds (brown algae / Phaeophyta)
How can algae be used to produce ethanol?
Algae can be anaerobically digested to produce methane followed by fermentation to make ethanol
How are algal species used in biodiesel production?
Some species have high polyunsaturated fatty acid concentrations, which render biodiesel to remain a fluid at a lower temperature
How much more oil do microalgae have in comparison to plant oil crops?
30x
and they don’t take up valuable land space
What can algae do to benefit the environment?
They can be used to clean up contaminated water
They can be an indicator of environmental change
They can be used to feed fish
What is Paulinella and what cyanobacterium does its chromatophore show similarities to?
Paulinella is a heterotrophic protist that has become photosynthetic.
It’s chromatophore shows similarities with the cyanobacterium Synechococcus.
It is debated whether the chromatophore is an endosymbiont or an organelle
What is the chromatophore in Paulinella an example of?
New primary endosymbiosis
Why can’t the chromatophore in Paulinella live independently?
When the chromatophore divides it needs instructions from the host.
How many genes does Paulinella contain from the chromatophore and what is this an example of?
33 genes from the chromatophore
This is an example of endosymbiotic gene transfer (EGT)
Definition of a true organelle:
A mechanism for importing of host nucleus-encoded proteins
What can happen to eukaryotes who no longer need organelles such as chloroplasts or mitochondria?
They may lose the organelle but retain the genes, or still possess a relict organelle carrying out vital enzyme reactions
What are diplomonads (order)?
Anaerobes
Lack plastids (double-membrane organelles)
Often parasites
What is the relic mitochondrion organelle called in Giardia (an anaerobic flagellated gut parasite)?
A mitosome
What is the relic mitochondrion organelle called in Trichomonas (an anaerobic parasite)?
A hydrogenosome
What are eukaryotic flagella called and what is their structure?
Undulipodia
9 + 2 arrangement of microtubules made of tubulin subunits, built from a basal body
Giardia have two forms, what are they?
Cyst phase - inactive form
Trophozoite - active form
What are the main features of Trichomonas (species)?
Reduced mitochondria called a hydrogenosome (produced hydrogen and ATP)
Substrate-level ATP synthesis (iron and amino acid metabolism)
What are the kinetoplastids (class)?
Eukaryotic flagellates
Some free-living, some parasitic
What type of unique DNA does a kinetoplastid possess?
kDNA in a structure called a kinetoplastid, in a single mitochondrion at the base of the flagellum
Example of a kinetoplastid, what does it cause and how is it transmitted?
Trypanosoma brucei, which causes sleeping sickness
Transmitted by the tse-tse fly
It has evolved elaborate mechanisms for repeatedly changing the antigens in the glycoprotein coat to dodge the antibodies of its host
What are apicomplexans? What are some of their features?
Spore-forming parasites of animals, which can cause some serious diseases
They are highly motile, with complex life cycles.
They are tolerant of rapid fluxes of O2 and CO2 concentrations
Apicomplexans are a merger of what two organisms?
Heterotrophic protists and red algae (Rhodophyta)
What is the relict chloroplast that Apicomplexan parasites rely on?
Apicoplast
Besides photosynthesis, what else are chloroplasts needed for?
Fatty acid synthesis
Synthesis of isoprenoid precursors
What are cilia?
Shortened versions of flagella that can operate in a coordinated fashion to achieve a certain movement
What are ciliates?
A large group of protists, named for their use of cilia to move and feed
What are the two nuclei in ciliates called, and what are they used for?
Micronucleus - responsible for reproduction
Macronucleus - responsible for vegetative functioning of organism
What do ciliates possess to help control their water balance when water around them fluctuates in salt concentration?
They possess food vacuoles for digestion and a contractile vacuole
What is the names for the stages when water flows into and out of a contractile vacuole?
Diastole - water flows in
Systole - water expelled out
What class does Trichomonas belong to?
Parabasalid
What are the cilia of ciliates called?
Cirri
What are the cilia of ciliates used for?
Generating feeding currents
What do ciliates feed on and how do they digest it?
They are predatory (active hunters)
They digest their prey in food vacuoles
What part do ciliates play in the rumen of cattle?
They supply some nutrients and regulate the bacterial population
What is the “King of the ciliates” and what are it’s features?
Diplodinium - very advanced ciliate but only single-celled
Has digestive system and complex mouth arrangement
What role do ciliates play in marine and freshwater food webs?
Channelling a significant amount of energy to the next tropic level
What are Rhizarians?
Diverse group of protists defined by DNA similarities
Which Rhizarian moves and feeds by pseudopodia?
Amoebas
What are pseudopodia?
Using a temporary protrusion of their flexible membrane for movement
What organism possesses tests made from calcium carbonate?
Foraminiferans (subphylum)
What are tests?
Porous, multi-chambered shells made mostly from calcium carbonate
Where do Foraminiferans (subphylum) live?
Mainly in sands, but there are some free-floating species
What are radiolarians (subphylum)?
Marine protists with tests fused into one delicate piece
What are the fused tests of Radiolarians (subphylum) made from?
Silica
How do Radiolarians feed?
They use their pseudopodia to engulf microorganisms through phagocytosis
What are Foraminiferans’ podia used for?
Swimming, collecting test material and feeding
Why is the classification of dinoflagellates as algae disputed?
They have unique nuclei and significantly larger genomes than other eukaryotic algae
What are the two major groups of diatoms?
Centric diatoms and pennate diatoms, depending on the form of their frustule
What shape are the pseudopodia of amoebozoans?
Lobe- or tube-shaped, rather than thread-like
What are amoebozoans?
Unicellular protists that live in soil and marine environments
What do amoebozoans eat and how to they ingest it?
Bacteria and protists, mostly by phagotrophy
What is the scientific name for slime moulds?
Dictyostelids
What are Dictyostelids and where are they common?
Large protists, common in damp soil and rotting wood
What do Dictyostelids (slime moulds) feed on?
Decaying organic matter
What is an example of a cellular slime mould?
Dictyostelium
What is an example of a plasmodial slime mould and what are it’s features?
Physarum
Single-called organisms but very large and multinucleate
What is the difference between cellular and plasmodial slime moulds?
The vegetative state of a cellular slime mould is a haploid amoeboid cell, whereas the vegetative state of plasmodial slime moulds is a multinucleate diploid amoeboid mass called a plasmodium
How many known species of brown algae are there?
1,500 - 2,000
