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Cell discovery and theory


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Cell discovery and theory

  1. 1. History of Cell Discovery
  2. 2. Daily Question:Brainstorm: What do you think of when you think of the word cell? Use a circle map to brainstorm
  3. 3. History*Cells were unknown until thediscovery of microscopes in the1650’s*two scientists workingindependently built the firstmicroscopes *Anton von Leeuwenhoek in Holland *Robert Hooke in England
  4. 4. *Leeuwenhoek*Studied pondwater, sour milk,and other fluids*named moving organisms“animalcules”scared people and caused asensation
  5. 5. Leeuwenhoek’sdrawings of“animalcules” set off aflurry of amateur andsometimes ridiculousclaims, such as:- pondwateranimalcules causingmadness!
  6. 6. *Hooke*Studied cork - a kindof tree bark*named the structureshe saw “cells” becausethey reminded him ofthe small roomsmonks slept in.
  7. 7. PauseTake two minutes to summarize yournotes into your own words.
  8. 8. *Spontaneous Generation From pre-historic times to about 1850, most people believed that under the right conditions, *living things could spontaneously appear from non-living material.
  9. 9. People throughout the Middle Ages believed that mice could be “created” spontaneously byputting grain in dark,quiet place and leaving it for a few weeks.
  10. 10. The discovery ofcells only confusedpeople more- Ifcells are alive,then where dothey come from? Can these almost invisible things appear spontaneously from the air?
  11. 11. *Francesco Redi *Born 1626 in Italy *First to challenge the idea of spontaneous generation Did not accept the common belief that flies magically appeared from rotting meat
  12. 12. Redi’s Experiment IV=cover DV=presence of flies Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies
  13. 13. Redi’s Conclusions Flies lay eggs, which grow into maggots, which metamorphose into flies Fly eggs If flies can’t lay eggs, then no new flies can grow
  14. 14. Objections to RediMany people rejected Redi’s claim thatflies do not spontaneously generateTheir reasoning: “sealing the jar closed prevented a magical essence from entering the rotting meat and brining it to life” “Scientists seek only to challenge belief systems and stir things up”
  15. 15. PauseTake two minutes to summarize yournotes into your own words.
  16. 16. *Lazzaro Spallanzani *1729. Italian *Believed microbes that spoil food come from the air and can be killed by boiling IV= air, DV=food spoilage Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil
  17. 17. Spallanzani’s Experiment Flask 1: boiled broth, open Flask 2: boiled broth, sealed shut Results Flask 1 spoiled Flask 2 did not spoil
  18. 18. Objections to Spallanzani Sealing the flask shut blocked the entrance of a magical life force in the air from getting to the broth. Since few people had seen these microbes, few people believed him.
  19. 19. *Louis Pasteur*1822. FranceSupported thatspontaneousgeneration is a myth*Inventedpasteurization(sterilization by heat)
  20. 20. Pasteur’s ExperimentAn improvement on Spallanzani’s workUsed special “swan-neck flasks” that allowedair in but kept bacteria outIV= bacteria, DV=spoiling brothHypothesis; If boiled broth is kept free ofbacteria, then it will not spoil even if air canreach it.
  21. 21. The curved neck allows air in but trapsbacteria-carrying dust and dirt particles
  22. 22. *Spontaneous generationis dead! Redi didn’t believe in it, and did an experiment using flies Spallanzani didn’t believe in it, and experimented with broth *Pasteur disproved it conclusively with his open-air yet spoilage free flasks.
  23. 23. Life from dead stuff= 0Biogenesis = 3 Experimental method wins out over superstition the cell theory takes hold among ordinary people
  24. 24. *Pasteur is the father ofmodern microbiologysupported the last part of the cell theory:cells only come from pre-existing cellsidentified yeasts as the microbes thatchange grape juice into wineshowed that heat can be used to sterilizefoods and preserve them in sealed glasscontainers, and later cans.
  25. 25. Finally... in the late 1870’s, doctors start to wash their hands and instruments before operating...some even start wearing gloves! Joseph Lister’s wacky idea that antiseptics kill germs catches on...
  26. 26. The Cell TheoryThe cell theory has three parts: All living things are composed of one or more cells Cells are the basic unit of structure and organization of all living things Cells can only come from pre-existing cells
  27. 27. *The cell theory1. *All living things contain at least one cell Many scientists working after Hooke and Leeuwenhoek observed different plants and animals Each of them noted that no matter what they observed, if it was alive it had cells.
  28. 28. 2. *Cells are the smallest living units ofmatter scientists quickly realized that when cells were dissected or broken open they died This meant that whatever “life” is, it is something that happens inside cells
  29. 29. *3. Cells can only come from pre-existingcells does not answer the question of where the first cell came from or how it came to be. has not been disproved yet- no scientist has ever built a living cell from nonliving organic molecules
  30. 30. *The cell theory is one ofthe most important theoriesin biology. All living things contain at least one cell Cells are the smallest living units of matter Cells can only come from pre-existing cells
  31. 31. And now…Use Google images (selectphotos) to find photographsof cells.Write a description of threecells that you see on yourpaper…
  32. 32. Complete theStudy Guide for ch 7.1If you finish early you may work oncredit Option A