If MITOCHONDRIA came from prokaryotes, how did eukaryotes synthesis ATP before the endosymbiosis?
Eukaryotes evolved from prokaryotes. The early prokaryotes probably obtained their energy differently from food sources. They had different chemical pathways. Since mitochondria evolved a more efficient way to extract energy, they helped those organisms that have formed a symbiotic relationship with them. Plants evolved from single celled organisms. They probably did not photosynthesize their own food originally. That is why they needed to engulf cynaobacteria. They were probably predatory organisms, otherwise they could not have ENGULFED anything. Correct? So, most likely plants were originally protozoans before they engulfed cyanobacteria and started photosynthesizing their own food.
