Which statement does not support the endosymbiotic theory?
Mitochondria and chloroplasts reproduce independently from the cell.
Mitochondria and chloroplasts contain their own ribosomes.
Mitochondria and chloroplasts have DNA that resembles bacterial DNA.
Mitochondria and chloroplasts are much larger than prokaryotic cells.
The Correct Answer and Explanation is:
Correct Answer:
Mitochondria and chloroplasts are much larger than prokaryotic cells.
Explanation:
The endosymbiotic theory is a widely accepted explanation for how eukaryotic cells (cells with nuclei and organelles) evolved from prokaryotic cells (simpler cells without nuclei). According to this theory, certain organelles within eukaryotic cells—mitochondria and chloroplasts—originated as free-living prokaryotic bacteria that were engulfed by a larger host cell. Instead of being digested, these bacteria formed a symbiotic relationship with the host cell, eventually becoming permanent structures inside the cell.
Several key pieces of evidence support this theory:
- Independent reproduction: Mitochondria and chloroplasts reproduce by binary fission, similar to bacteria, and independently of the host cell’s division process.
- Presence of ribosomes: Both organelles contain their own ribosomes, which resemble those found in bacteria, not in the eukaryotic cytoplasm. This supports the idea that they were once independent organisms.
- Bacterial-like DNA: Mitochondria and chloroplasts possess circular DNA, just like bacterial DNA. This is significantly different from the linear DNA found in the nucleus of eukaryotic cells.
The statement “Mitochondria and chloroplasts are much larger than prokaryotic cells” does not support the endosymbiotic theory. In fact, it contradicts one of the key arguments. According to the theory, these organelles originated from prokaryotes, so we would expect them to be similar in size or smaller than prokaryotic cells, not larger. In reality, mitochondria and chloroplasts are similar in size to modern bacteria, particularly proteobacteria (for mitochondria) and cyanobacteria (for chloroplasts).
Thus, the correct answer is the statement that misrepresents a key comparison of size and contradicts the foundational claims of the theory.