In recent times, significant interest has piqued in comprehending the evolution process of eukaryotes from prokaryotes. This study illuminates the complex question of how cells evolved to possess nuclei and organelles. The widely accepted endosymbiosis theory proposes that this evolutionary leap originated from a symbiotic relationship between an ancient archaeon (microorganisms that dwell in hostile environments) and a bacterium.
Defining Eukaryotes and Prokaryotes
Life forms on Earth, depending upon the cellular structure, are generally classified into prokaryotes and eukaryotes. Prokaryotes are organisms with cells that lack a true nuclear membrane enveloping their genetic material- usually a circular DNA molecule- and other membrane-bound organelles. This group comprises bacteria and archaea and is characterized by relatively small, simple cellular structures.
On the other hand, eukaryotes have well-defined, membrane-enclosed nuclei within their cells. These organisms also have a range of further membrane-bound organelles, including mitochondria, endoplasmic reticulum, Golgi apparatus, among others. All animals, plants, and fungi fall under the category of eukaryotes, whose primary characteristics include larger, more intricate cells with a nucleus and various organelles.
The Role of Endosymbiosis in the Development of Eukaryotes
Endosymbiosis is a biological phenomenon where one organism resides inside another, and both derive benefit from this association. According to the endosymbiotic theory, the pathway leading to the evolution of eukaryotes involved an archaeon incorporating a bacterium. The archaeon sheltered the bacterium, providing a consistent environment while the bacterium furnished energy to the host organism. Over time, this relationship turned symbiotic, resulting in a new cell type- a eukaryote. The bacterium transformed into mitochondria, an organoid responsible for cellular energy production.
In the case of plants, an additional endosymbiotic incident took place where a cyanobacterium evolved to become chloroplasts, the organelles that carry out photosynthesis. These symbiotic relationships fueled the rise of eukaryotes, allowing them to grow larger and more complex, thereby enabling them to adapt to various habitats.
Addressing Past UPSC Civil Services Examination Questions
In the 2012 prelims of the UPSC Civil Services Examination, questions were posed around ‘stem cells’, an integral area of biological study. One of these questions, seeking to test the candidate’s understanding of stem cells, presented three statements related to stem cells- their source, potential uses, and medical applications. To clarify, stem cells are essentially undifferentiated or “blank,” cells with the potential to metamorphose into cells serving manifold functions in different body parts. They’re not exclusive to mammals, contrary to popular belief, but are also present in other organisms, including plants. Hence, the assertion that stem cells can only be derived from mammals is false.
As stem cells can morph into other cell types, they hold great promise in treating and comprehending diseases. Scientists posit that stem cells can replace damaged organs or tissues, correct organ malfunctions, research genetic defects, probe the emergence of diseases or cancerous cells, and test new drugs for efficacy and safety. They can also be deployed for various medical therapies. Therefore, the statement affirming the potential use of stem cells for screening new drugs and conducting medical therapies is correct.