First event Last event Because prokaryotic cells cannot replicate, the ancestral
ID: 199071 • Letter: F
Question
First event Last event Because prokaryotic cells cannot replicate, the ancestral cell degrades them and engulfs new ones. The respiratory machinery of the proteobacteria is incorporated into the ancestral cell as a membrane-bound organelle. Aerobic proteobacteria are engulfed by an ancestral anaerobic cell. The plasma membrane of an ancestral anaerobic cell infolds. Evolution occurs over many generations, and the proteobacteria lose the ability to exist outside of the ancestral cell. The aerobic proteobacteria are protected by the ancestral cell and provide energy to the ancestral cell through aerobic respiration.Explanation / Answer
First events
1) The plasma membrane of an ancestral anaerobic cell infolds.
2) Aerobic proteobacteria are engulfed by ancestral anaerobic cell.
3) The aerobic proteobacteria are protected by the ancestral cell and provide energy to the ancestral cell through aerobic respiration.
4) Evolution occurs through many generations, and the proteobacteria lose the ability to grow outside the ancestral cells.
5) The respiratory apparatus of the proteobacteria is incorporated into the ancestral cell as a membrane bound organelle
Last event
Endosymbiotic Theory for Origin of Mitochondria:
An anaerobic prokaryote that was unable to utilize oxygen lost its cell wall. The elastic membrane beneath the cell wall enfolded and led to formation of the nucleus and the internal organelles of the cell. The primitive eukaryotic cell could engulf an aerobic proteobacteria (a prokaryote) via its cell membrane. The primitive eukaryote did not degrade the aerobic proteobacteria. There was a mutually beneficial relationship initiated wherein the eukaryote provided protection and nutrition to the proteobacteria while the proteobacteria provided energy via respiration. Over time, most of the genes were transferred to the nucleus and the endosymbiont could not live outside the host. It became dependent on the host cell for organic and inorganic nutrient. The respiratory apparatus became evolved, gained a double membrane and became a mitochondrion. The host cell now evolved to form respiring eukaryotic aerobe.
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