Evolution of Photosynthesis and Algae Flashcards
Autotroph
Definition
organisms that sustain themselves without eating anything derived from other organisms
producers of the biosphere
they produce organic molecules from carbon dioxide and other inorganic molecules
Heterotroph
Definition
obtain organic material from other organisms
almost all of them depend on photoautotrophs for food and oxygen
What do photosynthetic organisms do?
convert light energy into chemical energy
the chemical energy is used for carbon skeletons and synthesis of molecules etc.
Chloroplasts
- in leaves
- solar powered chemical factories
- contain chlorophyll
- light is absorbed by the chlorophyll and used to synthesise organic molecules in the chloroplast
Where in the chloroplast do the light reactions of photosynthesis take place?
thylakoid membrane
Where in the chloroplast do the dark reactions / the calvin cycle take place?
in the stroma
In which types of organisms does photosynthesis occur?
- plants
- algae
- prokaryotes
Evolutions of chloroplasts
-chloroplasts are similar to early photosynthetic bacteria
First photosynthetic organism
fossil finds and chemical evidence of organisms similar to cyanobacteria 2.5bya
Early Evolution of Photosynthesis
the presumed early evolution of photosynthesis is from anoxygenic photosynthesis
Origin of Carbon Fixation
Carbon isotope data suggests carbon fixation was occurring at east 1 billion years before the first photosynthesis
Anoygenic Photosynthesis
- metabolic complexity and diversity developed in prokaryotes
- produce ATP, take in CO2, no O2 production
- only one photosystem similar to PS1
- used photosynthetic pigments similar to chlorophyll called bacteriochlorophylls
Examples of Anoxgenic Photosynthetic Organisms
green sulphur bacteria
purple bacteria
heliobacteria
How did the transition from anoxygenic to oxygenic photosynthesis occur?
-when cyanobacteria learnt to use water as an electron donor (PS2)
How did the transition from oxygenic photosynthetic prokaryotes to oxygenic photosynthetic eukaryotes occur?
- 2.5 billion years ago
- primary endosymbiosis event
- a photosynthetic cyanobacterium was ingested (and not degraded) by a eukaryotic cell
What happened after the primary endosymbiosis event in the evolution of photosynthetic organisms?
- the ancestral eukaryote led to the evolution of algae
- diversification of algae
- the conquest of land
Photosynthetic Organisms
Purple Bacteria
prokaryotic
anoxygenic
electron donors = H2S, S, Fe2+
Photosynthetic Organisms
Cyanobacteria
prokaryotic
oxygenic
electron donor = O2
Photosynthetic Organisms
Algae
eukaryotic
oxygenic
electron donor = O2
Photosynthetic Organisms
Plants
eukaryotic
oxygenic
electron donor = O2
Atmospheric Oxygen
atmospheric oxygen is of biological origin
it is released in the hydrolysis of water in PS2
Atmospheric Oxygen Levels Over Time
1.5bya - O2 revolution correlates with formation of eukaryotic cells containing chloroplasts
750mya - increase in oxygen with increase in abundance of multicellular photosynthetic organisms
350mya - emergence of large vascular plants in the carboniferous leads to 30% increase spike in O2 levels
Multicellular Photosynthetic Life on Land - Problems With Carbon Dioxide
- not enough CO2 in the vicinity of chloroplasts
- stomata appear to have been a very early innovation
Photosynthetic Mechanism - Cyanobacteria vs. Land Plant Chloroplasts
- essentially unchanged
- no fundamental changes to the light reactions
- BUT more efficient carbon chemistry
- evolution of C4 and CAM photosynthesis
C4
- spatial separation of steps in the Calvin Cycle
- e.g. sugarcane
CAM
- crassulation acid metabolism
- temporal separation of the steps in the Calvin Cycle
- e.g. pineapple
Algae - Evolutionary History
- origin over 2bya
- less than 1bya, all algae live in the ocean
- 480mya, green algae make the transition tot land
- eukaryotic
Advantages of Algae Living in the Sea
- protected from drying out
- protected from UV radiation
- protected from large fluctuations in temperature
Macroalgae
seaweed (brown, red, green)
large, multicellular
rougly ressemble terrestrial plants but they aren’t related
Microalgae
golden algae, dinoflagellates, euglenoids, diatoms
single celled
Protists
- algae, human parasites, omycytes
- mostly unicellular
- autotrophic and heterotrophic
Green Algae
- charophtes and chlorophytes
- c.17 000 species
- marine and freshwater
- uni and multicellular
- colonial - form lose ‘multicellular’ associations in some parts of life cycle
- charophytes are the most recent common ancestor with land plats
Red Algae
- rhodophytes
- c.5000 species
- mainly marine
- non motile
- mostly unicellular but many multicellular
- red, but still do oxygenic photosynthesis
- most abundant large algae in tropical costal waters
Brown Algae
- phaeophytes
- 250 genera, 2000 species
- large, complex, multicellular
- found in all colder seas and oceans
- kelps - live in deep ocean
- thallus - algal body
- holdfast ~ roots
- stipe ~ stem
- blades ~ leaves
- cell wall source = sulphated fulcans and alginate polysaccharides
- most complex anatomy of all algae
Algae
- c. 70000 species
- vast diversity in morphology
- several groups of photosynthetic organisms that arose separately from non photosynthetic ancestors
- multicellularity arose several times among algal groups
- different cytoplasmic connections, not just plasmodesmata
Euglenoids
- 40 genera, c. 1000 species
- unicellular
- motile - flagella
- mainly fresh water
Diatoms
- c. 12 000 specices
- unicellular
- 2 part box, highly sculpted
- major component of phytoplankton
- highly diverse
Dinoflagellates
- 550 genera, c. 3000 species
- unicellular
- planktonic
- motile - flagella, 2 that spin to propel them through water
Golden Algae
- yellow / brown carotenoids
- bi-flagellated
- all are photosynthetic but some are also heterotrophic
Similarities between green algae and land plants
- cell walls containing cellulose
- chloroplasts containing chlorophylls A and B
- store food as starch
- closest lineage to plants
Chloroplasts in Green and Red Algae
derived from the primary endosymbiosis event 1bya
Chloroplasts in Most Other Algae
- 3-4 membranes
- not close relatives of green plants
- presumably acquired photosynthesis separately from red and green algae
Secondary Endosymbiotic Event
a photosynthetic eukaryote was ingested by a non-photosynthetic eukaryote, resulting in a new photosynthetic eukaryote
What are the three secondary endosymbiotic events?
- engulfing of a cyanobacterium led to photosynthesis in archaeplastida
- red alga -> chromalveolata
- green alga -> excavata
Classification of Organisms into Supergroups
Analysis of genomes led to the classification of organisms into the following groups:
- excavata
- SAR group (Chromalveolata and Rhizaria)
- Archaeplastida
- Urikanta
Supergroups and Photosynthesis
There are three super groups that contain photosynthetic organisms:
- excavata
- chromalveolata
- archaeplastida
