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Name: Burhan
Status: student
Grade: 9-12
Location: Outside U.S.
Country: Pakistan
Date: Fall 2013

So the evolution of Mitochondria and Chloroplast suggests that these two respectively were, billions and trillions of years ago, not part of animal and plant cells, but actually uni-cellular organisms that were engulfed by our cells and now have evolved to their current state as organelles. Chloroplast, as we all know is the only food manufacturing factory on the Earth. Mitochondria is responsible for aerobic respiration and is the Energy factory. My question is, HOW, those billion years ago, were plants and animals surviving without these extremely ESSENTIAL organelles in their cells. I looked up the net and nobody had a theory. Maybe somebody could give me an answer here

Hi Burhan,

Thanks for the question. To the best of my knowledge, there is no evidence of evolution trillions of years ago. According to the theory of evolution--which cannot be proved--there were no plants or animals billions of years ago. So the question of how plants and animals survived without chloroplasts and mitochondria is not applicable. I would recommend rephrasing the question.

I hope this helps. Please let me know if you have more questions. Thanks Jeff

Well, to answer your question-the fossil record shows us that animals and plants WEREN'T around at that time. Photosynthesis began in bacteria and that type of bacteria is still around today. Plants don't show up in the fossil record until later. OUR cells did not engulf mitochondria. Today's plants didn't engulf chloroplasts. The theory predicts that endosymbiosis occurred between two unicellular organisms, neither of which had a nucleus. One may have been larger than the other. If the smaller one could break down glucose in a more efficient manner than the larger one, they would both benefit from the relationship. The smaller one would live inside of another, have food to break down and perhaps have some left over to share with the larger one. This relationship would allow both to survive and reproduce more often than others of their species so the relationship gave them an advantage. If the same cell engulfed a photosynthesizing organism, then there was even more of an advantage. Multicellularity (ie plants and animals) came later. Of course, I wasn't there, and can't prove any of this. However, there is much evidence to support this idea. Mitochondria are the same size and shape as bacteria, they have one circular chromosome like bacteria do, they have their own ribosomes that resemble bacterial ribosomes and the sequence of the DNA in mitochondria matches bacteria DNA most closely.


Consider prokaryotes like bacteria. They lack mitochondria, yet they have still survived for eons. Bacteria still have the ability to respire and generate ATP, except that it's done "in-house" instead of offloading that duty to the endosymbiont (the mitochondria).

Prior to endosymbiosis, there were no green plants. When the milestone event that led to the engulfment of a chloroplast took place, it was found to be value-added and mutually beneficial for both parties. This totally upended life on earth. The atmosphere was now rich with oxygen, a normally toxic material. Organisms had to develop coping strategies to branch out into this uncharted territory. Green plants were one of the evolutionary outcomes.

Dr. Tim Durham Assistant Professor of Agronomy and Agricultural Science Ferrum College

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