Endosymbiosis

Outline

Ways that members of "algal" phyla get their energy -- some are:

autotrophic

heterotrophic

mixotrophic

auxotrophic

Endosymbiosis and the origin of chloroplasts

How do you get "normal" chloroplasts?

Normal chloroplasts (as in chlorophytes and Plantae):

• 2 membranes
• DNA
• ribosomes
• thylakoids

The process of endosymbiosis

1. Heterotrophic eukaryote eats prokaryotic autotroph by phagocytosis
2. Eukaryote engulfs but does not digest prokaryote
3. Prokaryote adapts, becomes able to reproduce in eukaryotic host
4. Prokaryote loses features needed for independent existence -- cell wall, much of DNA
5. Heterotrophic eukaryote is now an alga with a "normal" chloroplast

Glaucophytes

eukaryotic algae with "cyanelles" instead of chloroplasts

cyanelles

• chl a only
• single thylakoids
• phycobilisomes

dependent on host

Other kinds of chloroplasts in other phyla of algae

Vary in:

number of membranes -- 2, 3, 4, 5, etc.

pigments -- chlorophylls, phycobilins

thylakoids -- numbers in a stack

How do we get chloroplasts with 4 membranes?

1. Heterotrophic eukaryote 2 eats eukaryotic autotroph by phagocytosis
2. Eukaryote 2 engulfs but does not digest eukaryotic alga
3. Eukaryotic alga adapts, becomes able to reproduce in eukaryotic host
4. Eukaryotic alga loses features needed for independent existence -- cell wall, flagella, nucleus, cytoplasm and organelles
5. Heterotrophic eukaryote 2 is now an alga with a chloroplast with 4 membranes

• How do we get chloroplasts with odd numbers of membranes?  

  another method of ingestion beside phagocytosis

  heterotroph sucks out prey cell's cytoplasm into food vacuole

  Apparently chloroplasts have arisen many times in many different lineages

  Dinoflagellates are especially promiscuous in this regard

Vocabulary

click here to go to endosymbiosis vocabulary

on to the next topic -- dinoflagellates

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