Correct option is B
Explanation:
Primary plastids originated once by the engulfment of a cyanobacterium by a eukaryotic host, giving rise to the ancestral plastid lineage found in green algae, red algae, and glaucophytes.
Secondary endosymbiosis involved a eukaryote engulfing a red or green alga, giving rise to plastids in diverse algal groups like diatoms (from red algae) and euglenids (from green algae).
Tertiary endosymbiosis is a further engulfment of secondary plastid-containing algae, adding complexity to plastid evolution.
Statement 2 accurately captures the accepted model of plastid origin and diversification.
Information Booster:
The endosymbiotic theory explains plastid evolution as successive engulfments of photosynthetic organisms.
Primary plastids derive directly from cyanobacteria; secondary and tertiary plastids derive from eukaryotic algae.
Red algal plastids gave rise to heterokonts (brown algae, diatoms), while green algal plastids gave rise to euglenids and chlorarachniophytes.
Additional Information on Incorrect Options:
Option 1 incorrectly places red algae as the initial primary plastid ancestor.
Option 3 suggests multiple independent primary endosymbioses, which is not supported by evidence.
Option 4 misassigns primary plastids to secondary endosymbiosis and confuses tertiary endosymbiosis roles.
