Presentation is loading. Please wait.

Presentation is loading. Please wait.

Evolutionary origins of plants: algae  “Algae” is a historical term. It describes a number of groups of organisms that are plant-like in that they contain.

Similar presentations


Presentation on theme: "Evolutionary origins of plants: algae  “Algae” is a historical term. It describes a number of groups of organisms that are plant-like in that they contain."— Presentation transcript:

1 Evolutionary origins of plants: algae  “Algae” is a historical term. It describes a number of groups of organisms that are plant-like in that they contain chloroplasts and carry out photosynthesis but are outside the lineage of plants.  “Algae” is a paraphyletic group i.e. does not consist of an ancestor and all of the ancestor’s descendents.

2 Algae  Algae have a widespread occurrence Aquatic: marine, freshwater Aquatic: marine, freshwater Terrestrial: deserts, soils, trees, rocks, etc Terrestrial: deserts, soils, trees, rocks, etc Some are symbiotic Some are symbiotic e.g. lichen is a symbiotic alliance between a fungus and an alga.e.g. lichen is a symbiotic alliance between a fungus and an alga. e.g. Green Algae (zooxanthellae) live within reef building corals.e.g. Green Algae (zooxanthellae) live within reef building corals.

3 Growth forms of algae  Algae take on a variety of forms both microscopic and macroscopic  Unicellular  Colonies  Filaments  Multicellular thallus

4 Ecological Importance of algae  Are very important primary producers especially in marine ecosystems.  Play major roles in global cycling of C, N, and O 2.  Their photosynthetic activity forms the basis of complex communities.

5 Major groups of algae  Red algae: Rhodophyceae  Brown algae: Phaeophyceae  Green algae: Chlorophyta

6 Rhodophyceae (red algae)  Fossil record: BYA  ~ 5,500 species Mostly marine, few freshwater  Live attached to surfaces (rocks, shells, other algae)  Many are reef-building algae (corallines: CaCO 3 accumulates in cell walls)

7 Rhodophyceae (red algae)  Body forms: Unicellular, simple filaments or complex filamentous aggregations  Chlorophyll a  Cell walls: cellulose, some with CaCO 3

8 Phaeophyceae (brown algae)  Largest and most complex algae.  All are multicellular and most are marine.  Body form: Thallus (plant-like but lacks true roots, stems and leaves).  Thallus includes holdfast, stipe and leaflike blades.  Include the largest seaweeds such as the kelps.  Cell walls contain cellulose.  Chlorophyall a and c.

9 Kelp Forest, New Zealand – Ian Skipworth

10 Chlorophyta (green algae)  Fossil record: BYA  ~ 8,000 species (500 genera)  Marine, freshwater, terrestrial.  Attached or planktonic.  Chlorophyll a and b.  Many species form symbiotic relationships with other organisms.  Unicellular, filaments, colonies, also thallus body form.

11 Chlorophyta (green algae)  Cell walls: absent, cellulose, or modifications  Land plants are derived from green algae.  Many taxonomists believe green algae (and red algae) should be included among the Plantae.

12 Endosymbiosis  Symbiotic organisms are those that have a close mutually dependent relationship with another organism.  An endosymbiont is a cell that lives within another cell.  The forerunners of modern eukaryotic cells are believed to have been symbiotic associations of prokaryotic cells.

13 Endosymbiosis  The role of endosymbiosis in evolution was developed most extensively by Lynn Margulis of the University of Massachusetts.

14 Endosymbiosis  The proposed ancestors of mitochondria most likely were aerobic heterotrophic bacteria.

15 Mitochondria  Mitochondria contain own DNA (circular plasmids like bacteria)  Likely originated as aerobic bacteria, then engulfed ~1.5 Billion Years ago

16 Chloroplasts  Chloroplasts are believed to be descendents of photosynthetic prokaryotes (most likely cyanobacteria) that became endosymbionts within larger cells.  About 1.5 mya thus the first “plants” evolved from the engulfing of a photosynthetic prokaryote by an aerobic eukaryote.

17

18 Ploidy Level  How many sets of chromosomes?  Diploid (2n) - “typical” 2 forms of each gene (alleles) 2 forms of each gene (alleles)  Haploid (1n) - ex. sex cells Single copies; product of meiosis Single copies; product of meiosis  Polyploid (4n, 8n, 6n…) - anything more than 2n

19 Animals: One animal, one generation  Single generation is diploid (2n) Produces short- lived haploid (n) sex cells Produces short- lived haploid (n) sex cells 2n = 46 2n = 46 n = ?? n = ?? Paul Decelles

20 Plants: One plant, two generations  One generation is diploid (2n) Produces n spores that grow into… Produces n spores that grow into…  One generation is haploid (1n) Produces n gametes - later fuse and make a 2n individual Produces n gametes - later fuse and make a 2n individual Paul Decelles

21 Plants: “One plant is always two”  One generation is diploid (2n) Produces n spores Produces n spores  One generation is haploid (1n) Produces 1n gametes - later fuse and make a 2n individual Produces 1n gametes - later fuse and make a 2n individual SPOROPHYTE “spore [producing] plant” GAMETOPHYTE “gamete [producing] plant”

22 Alternation of Generations

23 Alternation of generations  Usually the diploid sporophyte is dominant and most obvious Examples: Examples: A fernA fern A pine treeA pine tree A Venus fly-trapA Venus fly-trap

24 Alternation of generations  …the exception: Bryophytes Gametophyte is dominant Gametophyte is dominant The “green plant” that you see is the gametophyte The “green plant” that you see is the gametophyte

25 Alternation of generations  …and the moss sporophyte is dependent Sprophyte is parasitic on the gametophyte Sprophyte is parasitic on the gametophyte Sporophyte Gametophyte

26 Alternation of generations  Two generations nearly always physically linked  PARASITISM is common Gametophyte Moss Sporophyte

27 Parasitic generations Plant groupParasitic generation Dominant generation Bryophytes Sporophyte Gametophyte Gymnosperms Gametophyte Sporophyte Angiosperms Gametophyte Sporophyte

28 Gymnosperms and Angiosperms  Parasitic reduction of the gametophyte  Two genders: Female gametophyte Female gametophyte Housed in the sporophyte ovuleHoused in the sporophyte ovule Male gametophyte Male gametophyte Housed in the pollen grainHoused in the pollen grain

29 And ferns?  Each generation is independent  Except for a short time when the sporophyte originates from the prothallus Fern Gametophyte Sporophyte Gametophyte


Download ppt "Evolutionary origins of plants: algae  “Algae” is a historical term. It describes a number of groups of organisms that are plant-like in that they contain."

Similar presentations


Ads by Google