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17.4: Photosynthetic Heterokonts - Descendents of Secondary Endosymbiosis

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  • The photosynthetic lineages of the heterokonts derived their golden brown chloroplasts from secondary endosymbiosis. In this event, an ancestral oomycete engulfed a red alga. As in primary endosymbiosis, instead of being digested, overtime the red alga degenerated into a chloroplast, this time with 4 membranes -- the engulfing membrane from the oomycete, the red alga’s plasma membrane, and the two membranes of the original chloroplast within the red alga. Note: In many groups derived from secondary endosymbiosis, the chloroplast has lost one of these membranes.

    The process of secondary endosymbiosis is shown on the following page. Add arrows to show the sequence of events. Label the heterotrophic oomycete, the photosynthetic red alga, and the origin of each membrane of the 4-membrane chloroplasts.


    The red algal cell would also have mitochondria. Feel free to add one in!

    Secondary Endosymbiosis in Heterokonts:

    Figure \(\PageIndex{1}\): Secondary Endosymbiosis

    Brown algae and diatoms are the result of this endosymbiotic event. Their chloroplasts have chlorophyll a, chlorophyll c, and fucoxanthin. Which pigment(s) are ancestral from secondary endosymbiosis (present in the red alga)?

    Which pigment(s) were derived after this event (not present in the red alga)?

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