Cells I. The Discovery of Cells A. What are cells? 1. the foundation for all life forms; all life functions begin with cellular processes 2. the smallest unit that retains all the characteristics of life 3. A collection of organelles, each with particular function, held together by a selectively permeable membrane B. The Cell Theory 1. All organisms are composed of one or more cells a. unicellular: one cell b. multicellular: many cells, often organized into specialized tissues, organs, systems 2. The cell is the basic unit of structure and organization of organisms 3. All cells come from preexisting cells. a. cells divide to produce two identical daughter cells b. disputed previous beliefs of spontaneous generation, homonculus, etc. C. How we arrived at what we know: 1. 384BC - Aristotle theorized that each germ must have come from another 2. 1665 - Robert Hooke - an English scientist ; used a light microscope to look at thin layers of cork. Discovered small boxes that resembled rooms at a monestary; called these "cellulae" (small rooms) 3. 1674 - 1683 - Anton von Leeuwenhoek - a dutch scientist designed his own microscope and discovered what he thought were living organisms in pond water, milk, body fluids, scrapings of scum on his teeth, etc. 4. a. called them "animalcules" b. discovered bacteria and protozoans 1668 - Francesco Redi - disproved spontaneous generation with maggot experiments a. one of the first scientific experiments conducted with proper controls and isolated variables b. spontaneous generation - the idea that living organisms can originate from non-living matter 5. 1802 - Lorenz Oken began the idea of the modern cell theory by stating that all living organisms originate from and consist of cells 6. 1833 - Robert Brown - observed plant cells and discovered, as well as named, the nucleus: recognized that is an essential organelle in cells and stressed its importance in reproduction 7. 1838 - Matthias Schleiden - German scientist that looked at plant tissue and concluded that they were composed of cells; cells are the basic building blocks of life 8. 1839 - Theodore Scwann - German scientist that observed animal cells and reached same conclusions as Matthias Schleiden; showed that plant and animal cells are fundamentally similar. Determined that cells are the basic unit of life. 9. 1855 - Rudolf Virchow - German scientist - published research that cells come from preexisting cells 10. 1857 - Albert Von Kolliker - discovered mitochondria 11. 1860 - Louis Pasteur - French physician that developed germ theory and said microorganisms cause disease. Supported idea that cells come from preexisting cells. 12. 1869 - Friedrich Meischner - isolated DNA 13. 1879 - Walther Flemming - described chromosome behavior 14. 1960's - Lynn Margulis - An American scientist that proposed that eukaryotic cells arose from a symbiotic relationship between prokaryotic cells (mutualism); The Endosymbiant Theory D. The Endosymbiant Theory: (endo = inner; symbiant = relationship) 1. Observed unicellular organisms and noted that some bacteria resemble chloroplasts in size, structure, and function (photosynthesis); some bacteria resemble mitochondria in structure and function (cellular respiration) 2. Both chloroplasts and mitochondria contain their own unique DNA similar to the DNA found in prokaryotes and not like the DNA found in eukaryotic cells; also have their own ribosomes and reproduce independently of the cells that contain them. 3. Reasoned that one prokaryotic cell was engulfed by another; once inside, the cell that was engulfed processed energy for both cells; the cell that did the engulfing provided the food sources broken down through respiration 4. The same was true for prokaryotes that resembled chloroplasts; a prokaryote capable of photosynthesis was ingested by another prokaryote and ultimately carried on the process for both cells; in exchange, a food source for respiration, protection, etc. was provided for the inner cell.