No, not all eukaryotes have mitochondria. While mitochondria are a defining characteristic of eukaryotic cells, some eukaryotes have lost them over evolutionary time.
This understanding contrasts with the traditional definition, as highlighted by Karnkowska, which states that the presence of mitochondria defines eukaryotic cells. However, scientific advancements have revealed exceptions to this rule.
Here's a more detailed breakdown:
- Traditional View: For a long time, the presence of mitochondria was considered a universal feature of all eukaryotic cells.
- Emerging Evidence: Research has identified eukaryotic organisms that lack mitochondria. These organisms are often adapted to anaerobic (oxygen-poor) environments.
- Evolutionary Loss: These eukaryotes are believed to have once possessed mitochondria but lost them or significantly modified them during their evolution. In some cases, mitochondrial remnants called mitosomes or hydrogenosomes are present. These organelles are derived from mitochondria but have specialized functions, such as hydrogen production in anaerobic conditions, instead of typical mitochondrial functions like ATP production via cellular respiration.
Examples of Eukaryotes Lacking "Typical" Mitochondria:
- Monocercomonoides: This is a genus of amitochondrial flagellates that completely lacks mitochondria, mitosomes, and hydrogenosomes.
- Giardia intestinalis: This parasitic protist has mitosomes, which are reduced mitochondria that lack a genome and electron transport chain.
- Other examples include some members of the Oxymonadida group.
In summary: While mitochondria are common in eukaryotic cells, the discovery of eukaryotes that have either lost mitochondria completely or possess highly modified versions demonstrates that they are not a universal feature. The definition of a eukaryote is, therefore, more nuanced than simply "having mitochondria."
