Question

There are many early evolutionary steps of photosynthetic organisms from the appearance of photosynthesis to various types of photosynthetic apparatus in the eukaryotic algae. Explain ten steps and how each advances a certain set of organisms.

Answer 1

Evolution of Photosynthesis:

Evolution of photosynthesis refers to the origin of photosynthesis and evolution to other organisms.

• It uses water as the source of electrons in photosynthesis, which has evolved in extant cyanobacteria.
• Through the action of endosymbiosis by which cyanobacteria would have entered into the cell of eukaryotes and over the time it would have converted into the cell organelle plastids.
• Photosynthesis further spread through secondary endosymbiosis resulting in complex photosynthesis in eukaryotes.

Secondary endosymbiosis - when a eukaryotic ell engulfs another eukaryotic cell which has already undergone endosymbiosis is called secondary endosymbiosis.

• Non photosynthetic plastids are also seen in parasitic microorganism apicoplasts, temporary loss of plastids are seen in kleptoplasty.

• Four major algal taxa contain plastids descended secondarily from red algal primary plastids; they are Cryptophyta Ochrophyta, Haptophyta, and Dinophyta (dinoflagellates).
• Cryptophyte plastids evolved from red algae.
• From cryptophytes ochrophyte–haptophyte plastids would have evolved. But evidence unclear.
• Variety of plastid are found in dinophyta

The most important dinoflagellate plastid is the peridinin-type plastid

1. they are Bounded by three membranes
2. Thylakoids are in groups of three
3. It Lacks lamellae
4. Chlorophylls a, and c with fucoxanthin is the major accessory pigment
5. Dinoflagellates with this plastid type have a nuclear-encoded form II rubisco, and do not have rubisco in their chloroplast genomes.

• Some species example: Gymnodinium breve have fucoxanthin as accessory pigments.

1. It shows to have acquired their plastids from haptophytes.
2. Plastid ultra structure resembles that of haptophyte plastids
3. Rubisco I is encoded in the chloroplast genome.

• Oomycetes and aplastidal heterokonts do not have plastids – plastids would have been lost during the evolution.