Question

Biologists think that endosymbiosis gave rise to mitochondria before plastids partly because

a. the products of photosynthesis could not be metabolized without mitochondrial enzymes.
b. all eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids.
c. mitochondrial DNA is less similar to prokaryotic DNA than is plastid DNA.
d. without mitochondrial CO2 production, photosynthesis could not occur.

Answer 1

b. all eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids.

Step-by-step explanation:

It is a fact that among eukaryotes, all the reresentatives of the Domain (Eukarya) have mitochondria (more or less modified) but not all of them posses plastids.

Indeed, only a selected group of eukaryotes have acquired plastids. This group includes the autothropic algae (e.g. green algae or Chlorophytes, red algae or Rodophytes, brown algae or Phaeophyceae, etc), briophytes, and traqueophytes (vascular plants, pteridophytes, conifers and flowering plants). The endosymbiotic event that led to the formation of a plant cell initially involved an eukaryotic heterotrophic cell (that already had mitochondria and nucleus) which phagocyted a cyanobacterium. Over time, this cyanobacterium transformed into the plant cell's plastid.