The Prokaryotes came first.
It is a commonly observed fact that complexity increases as we move on from a lower organism to a higher organism; these higher organisms appeared in the later stages of evolution. Their cells and organs became more and more specialised. We shall extend the same analogy to the evolution of cells.
A prokaryotic cell is extremely simple in structure and organisation. It is just a mass of cytoplasm surrounded by a membrane. Ribosomes and chromatin fibres are scattered inside. A eukaryotic cell is much more complex. Its chromatin fibres are enclosed in a nuclear membrane. There is a division of labour between different parts of the cell, each of the specialised parts enclosed by intracellular compartments. There is also a well-developed cytoskeleton.
We may safely deduce that in the beginning there were only prokaryotes. Ancient Fossil evidences support this assertion. Moreover, even today their descendants are found in every nook and corner of the planet, including the unimaginably cold and dark ocean depths, as well as the hot bubbling volcanoes and the poisonous sulphur springs - the conditions in the ancient earth must have been this extreme - and so ancient must be our prokaryotes.
Over the time, as the conditions settled down and the atmosphere seemed more pleasant, few of the prokaryotes decided to take some risk. The population had already increased manifold and food resources were dwindling. Many of the bacteria (prokaryotes) chose one of three ways:
Some bacteria started harnessing the solar energy to make food via photosynthesis. Others modified the way they were breaking down glucose so that they could obtain maximum energy from it. Still others started eating up each other. These bacteria became specialised as predators and they developed a strong cytoskeleton for better locomotion and engulfing motions. Their nuclear matter needed protection too and hence they developed a nuclear membrane by extending inward a part of the cell membrane, creating the endoplasmic reticulum along.
Organelles budded off this endoplasmic reticulum... and thus formed the Eukaryote.
Someone of these primitive eukaryotes ate up that prokaryote which could breakdown glucose very efficiently. This prokaryote proved to be quite strong as it continued to survive even inside the cytoplasm of the eukaryote. Today, this prokaryote is called mitochondrion. The eukaryote too lost interest in trying to digest it, as it was producing a lot more energy than it required and the eukaryote could use this up. It gave this particular eukaryote such a great evolutionary advantage that today it is hard to find a eukaryote without the mitochondria. In fact, it is more probable that that this event occurred before the development of organelles in the eukaryote because such complex developments couldn’t have proceeded without the vast amount if energy produce by the mitochondria.
On another occasion a Eukaryote might have swallowed a photosynthetic prokaryote, which was eventually known as chloroplast- thus started the story of plant cells.
So in every way that we see, and the deeper we look into the possible evolutionary development in accordance to most believable mechanisms, the more we believe that it were the prokaryotes that came first.
It is a commonly observed fact that complexity increases as we move on from a lower organism to a higher organism; these higher organisms appeared in the later stages of evolution. Their cells and organs became more and more specialised. We shall extend the same analogy to the evolution of cells.
A prokaryotic cell is extremely simple in structure and organisation. It is just a mass of cytoplasm surrounded by a membrane. Ribosomes and chromatin fibres are scattered inside. A eukaryotic cell is much more complex. Its chromatin fibres are enclosed in a nuclear membrane. There is a division of labour between different parts of the cell, each of the specialised parts enclosed by intracellular compartments. There is also a well-developed cytoskeleton.
We may safely deduce that in the beginning there were only prokaryotes. Ancient Fossil evidences support this assertion. Moreover, even today their descendants are found in every nook and corner of the planet, including the unimaginably cold and dark ocean depths, as well as the hot bubbling volcanoes and the poisonous sulphur springs - the conditions in the ancient earth must have been this extreme - and so ancient must be our prokaryotes.
Over the time, as the conditions settled down and the atmosphere seemed more pleasant, few of the prokaryotes decided to take some risk. The population had already increased manifold and food resources were dwindling. Many of the bacteria (prokaryotes) chose one of three ways:
Some bacteria started harnessing the solar energy to make food via photosynthesis. Others modified the way they were breaking down glucose so that they could obtain maximum energy from it. Still others started eating up each other. These bacteria became specialised as predators and they developed a strong cytoskeleton for better locomotion and engulfing motions. Their nuclear matter needed protection too and hence they developed a nuclear membrane by extending inward a part of the cell membrane, creating the endoplasmic reticulum along.
Organelles budded off this endoplasmic reticulum... and thus formed the Eukaryote.
Someone of these primitive eukaryotes ate up that prokaryote which could breakdown glucose very efficiently. This prokaryote proved to be quite strong as it continued to survive even inside the cytoplasm of the eukaryote. Today, this prokaryote is called mitochondrion. The eukaryote too lost interest in trying to digest it, as it was producing a lot more energy than it required and the eukaryote could use this up. It gave this particular eukaryote such a great evolutionary advantage that today it is hard to find a eukaryote without the mitochondria. In fact, it is more probable that that this event occurred before the development of organelles in the eukaryote because such complex developments couldn’t have proceeded without the vast amount if energy produce by the mitochondria.
On another occasion a Eukaryote might have swallowed a photosynthetic prokaryote, which was eventually known as chloroplast- thus started the story of plant cells.
So in every way that we see, and the deeper we look into the possible evolutionary development in accordance to most believable mechanisms, the more we believe that it were the prokaryotes that came first.
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