[Campbell Biology P.665] Apicomplexan parasites, such as Plasmodium, possess modified plasti... | Practice Question

Apicomplexan parasites, such as Plasmodium, possess modified plastids despite not being photosynthetic. Based on the concept of endosymbiosis presented in the text, which of the following is the most plausible hypothesis for the presence of these non-photosynthetic plastids?

  • A: These plastids were acquired directly from ingesting free-living photosynthetic bacteria by the parasites.
  • B: The modified plastids are vestiges of a photosynthetic ancestry, having lost their photosynthetic function over evolutionary time.
  • C: These plastids primarily serve as structural support elements within the parasite's cell.
  • D: The plastids were acquired through horizontal gene transfer from their eukaryotic host organisms.

Explanation

The text states that plastids originated from cyanobacteria via primary endosymbiosis, forming red and green algae, and that 'Other protist groups evolved from secondary endosymbiotic events in which red algae or green algae were themselves engulfed.' Apicomplexans part of Alveolates within SAR are known to have obtained their plastids called apicoplasts via secondary endosymbiosis from a red alga. The hypothesis is that these plastids, while no longer photosynthetic, are remnants of this photosynthetic ancestry, having been modified to serve other essential functions for the parasite.