American anatomist Ivan Wallin ($${}1883$$–$${}1969$$) furthered the endosymbiotic hypothesis by experimentally testing the similarities between mitochondria, chloroplasts, and bacteria in the $${}1920$$s. He published several papers supporting the hypothesis, including a $${}1926$$ co-authored work with Konstantin Mereschkowski. Wallin claimed to culture mitochondria outside their host cells, but scientists dismissed this as bacterial contamination. Modern genome sequencing supports his critics, revealing that much of the mitochondrial genome transferred to the host cell's nucleus, preventing independent mitochondrial life.

Ivan Wallin

Following Ivan Wallin's early experimental work, the endosymbiotic hypothesis was largely ignored for $${}50$$ years because scientists were unaware that organelles contained their own DNA. However, the hypothesis was resurrected in the $${}1960$$s with the discovery of mitochondrial and chloroplast DNA.

Resurrection of the Endosymbiotic Hypothesis

Based on the ability of chloroplasts to reproduce independently, Russian botanist Konstantin Mereschkowski ($${}1855$$–$${}1921$$) suggested in $${}1905$$ that chloroplasts may have originated from ancestral photosynthetic bacteria living symbiotically inside a eukaryotic cell. He proposed a similar origin for the nucleus of plant cells. This represented the first articulation of the endosymbiotic hypothesis to explain how eukaryotic cells evolved from ancestral bacteria.

Google

A multi-membrane organelle where photosynthesis occurs in eukaryotes

Chloroplast

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

In the early $${}1880$$s, German botanist Andreas Schimper ($${}1856$$–$${}1901$$) became the first to describe the chloroplasts of plant cells. He identified their crucial role in starch formation during photosynthesis and noted that chloroplasts divided independently of the cell's nucleus.

Andreas Schimper

Konstantin Mereschkowski

The modern endosymbiotic theory states that mitochondria and chloroplasts arose as a result of prokaryotic cells establishing a symbiotic relationship within a eukaryotic host. Mounting genetic evidence, particularly from DNA sequencing, supports this theory by demonstrating similarities between these organelles and bacteria.

Learn Before

Related

Learn After