Algae
Photosynthetic protists who
gained oxygenic photosynthesis via primary or secondary endosymbiosis
Primary production on Earth
via photosynthesis
- 30% by algae
- 20% by prokaryotes such as cyanobacteria
- 50% by land plants
Algal Blooms
Rapid growth of ‘algae’ due to increase in nutrients etc.
* Runoffs from fertilized agriculture lands, untreated factory waste water, etc., can be sources of increased nutrients
- Caused by both algae and cyanobacteria
- Usually, one species dominate a bloom at any given time, but the dominant species may change over time
Algal blooms and environmental concerns
- Damages environment and its inhabitants
- Water hypoxia through bacterial decomposition of dead algae
- Mechanically damaging gills
- Production of algal toxins
Damages fish by adhesion to gills and
production of neurotoxins
- Concerns for environmental conservation and economic damage by affecting aquacultures and tourism
- Harmful algal blooms increasing due to climate change
Red tides
- Alveolate in the SAR supergroup
- Unicellular algae
- About half are chemoheterotrophs, others are photoautotrophs /mixotrophs
Photoautotrophic dinoflagellates contain carotenoids as one of their photosynthetic pigments - Carotenoids are orange pigments
Algal bloom of dinoflagellates causes red tide
* ‘Red tide’ is caused by other algae too, such as Heterosigma akashiwo
Haptophytes
- ‘Unresolved’ group in the eukaryotic phylogenetic tree
- Mostly marine, unicellular photoautotrophs and mixotrophs
- Two flagella for motility plus a haptonema for surface attachment and/or predation
- Surface of haptophytes are covered with small scales made of polysaccharides
- Some haptophytes like Emiliana hyxleyi have hard, calcified scales
Emiliania hyxleyi and the cliffs of Dover
- Blooms of Emiliania huxleyi can be seen from outer space
- Dead bodies of these calcified haptophytes accumulated on ocean floors over long time, which became enormous structures like the cliffs of Dover
Stramenopiles, of SAR supergroup
- Straw-hair (Latin, Stramen-pilos), as
many members have flagellum with fine, hairlike projections - Diatoms, a unicellular, photoautotrophic Stramenopile
- One of the most abundant photosynthetic organisms in oceans and lakes
- Diatoms have glass-like cell wall made of silicon dioxide for mechanical protection vs. predation
Diatoms of various shapes are distributed
in aquatic systems such as oceans, rivers and lakes
* Distribution is correlated reasonably well with location, season, etc
Diatoms are well preserved due to their silica shell
Forensic limnology isolates diatoms from
crime scenes to better understand the case
* For example, using diatoms on victim body to match it to the crime location
* Not as useful as legal evidences due to the amount of variation in samples
Brown algae (seaweeds)
- Multicellular photoautotrophic
Stramenopile, and the largest, most complex algae - Have organ-like structures which are analogous to plants
- Blades: increase surface area (leaf-like)
- Stipe: support the blades (stem-like)
- Holdfast: anchor the alga (root-like)
- Can get up to 60 m tall
- Some have gas-filled floats to help the
blades get closer to the water surface - Plant-like reproduction cycle
Alternating diploid and haploid stages
- Diploid: Cell with a pair of chromosomes (2n)
- n=23 for human, 46 chromosome total
- Haploid: Cell with a single set of chromosome (n)
Reproduction in humans example
- Diploid adult (n=46) produces haploid, unicellular gametes (sperm/egg, n=23) via meiosis
- Haploid sperm (n=23) fuses with haploid egg
(n=23), producing a diploid, unicellular zygote (n=46) - Diploid zygote divides by mitosis to grow into diploid adult (n=46)
Alternation of generation definition
For reproductive cycle of animals,
multicellularity only occurs during the diploid stage
Alternation of generation: Plants and some algae produce multicellular bodies in both diploid and haploid stages
Alternation of generation alternates between
- Sporophyte: Spore-producing, diploid
multicellular form - Gametophyte: Gamete-producing, haploid multicellular form
Distinguishing feature of all plants and some algae
Alternation of generation process
- Diploid sporophyte produces haploid spores by meiosis
- Haploid spores divide by mitosis to become the haploid gametophyte
- Haploid gametophyte produces haploid gametes by mitosis
- Two haploid gametes fuses, producing a diploid, unicellular zygote
- Diploid zygote grows by mitosis to become the diploid sporophyte
Alteration of Generation in Brown algae
- Example: Laminaria sp.
- Brown algae spores are called
zoospores since they can move with flagella - About half of zoospores develop into
haploid multicellular female gametophyte, the other half develop
into male gametophyte - Female and male gametophytes
produce gametes (egg and sperm),
which meet and fertilize into the
diploid zygote
Archaeplastida
- Direct ancestors of primary endosymbiosis
- The ‘source organisms’ of secondary
endosymbiosis
Green algae
‘Green algae’ is a paraphyletic group which is missing the Embryophytes (plants)
Two main groups of green algae:
- Chlorophytes: the sister group to the clade Streptophyta (Charophytes + plants)
- Charophytes: the closest relative to land plant
Charophytes, Green algae
- Closest relative to plants
- Determined by molecular phylogeny of nuclear, mitochondrial and plastid DNA, as well as morphological features
Charophytes and plants:
- Both synthesize cell wall using ring like protein structure, embedded in plasma membrane
- Both have flagellated sperm
- Both have similar nuclear, mitochondrial and chloroplast DNA
- Both have sporopollenin
Sporopollenin:
tough layer which surrounds charophytes zygotes to prevent it from drying out
Sporopollenin eventually enabled ancestral charophytes to live permanently on land, above water surface
Plants have sporopollenin walls which encase plant spores
