Where do cells come from? Scientists in the 1800s proposed an answer to this question by stating that all organisms are made of cells, and all cells arise from preexisting cells. This hypothesis, later to become the cell theory, was a direct challenge to an alternate hypothesis called spontaneous generation. Scientists design experiments to test the validity of hypotheses. Louis Pasteur designed what is now a classic experiment to test the hypothesis of spontaneous generation. His hypothesis was that if cells arise from nonliving substances, they will appear in sterile broth. He created two treatment groups: a broth that was exposed to a source of cells, and a broth that was not. For his control treatment, Pasteur used a straight-necked flask to separate the broth from the surrounding air. For his experimental treatment, he used a swan-necked flask. The neck shape and length assured that no cells were entering the flask from the air. Pasteur then performed the same procedure on these two flasks. He boiled the broth to kill any existing organisms. He then let the broth cool and allowed it to sit for several days, after which he checked for the growth of any organisms. Pasteur found living organisms only in the control flask. Because the experimental flask remained sterile, the hypothesis of spontaneous generation was rejected. By changing a single variable-the shape of the flask-Pasteur was able to conclude that cells were not generated spontaneously but were actually entering the broth from the surrounding air. Microorganisms, carried by dust particles, fell into the straight-necked flask. However, the swan neck trapped the particles, preventing cells from entering the broth. Let's examine a set of experiments using two types of flies: houseflies and Zonosemata vittigera flies. Unlike houseflies, Zonosemata have dark wing bands and a habit of waving their wings when disturbed. This wing-waving behavior has been observed only in the presence of Zonosemata's major predator, the jumping spider. The jumping spider also has dark bands-but on its legs-and has a territorial display of waving its legs. In this activity, you will test the hypothesis that Zonosemata flies mimic jumping spiders to deter predation by the spider-in effect, leading the spider to mistake the fly for another spider. We can break down the hypothesis into three questions, using three experimental groups: Question 1: How does the presence of wing bands alone affect predation by jumping spiders? To answer this question, Zonosemata wings can be surgically removed and glued onto houseflies. Question 2: How does the use of wing waving alone affect predation by jumping spiders? To answer this question, housefly wings can be surgically removed and glued onto Zonosemata. Question 3: How does the presence of both wing bands and wing waving affect predation by jumping spiders? Intact Zonosemata can be used to answer this question. Control groups are needed to ensure that any variation is the result of a treatment specifically related to the hypothesis being tested. In this experiment, control groups test the following questions: Question 4: How does the lack of wing bands and wing waving affect predation by jumping spiders? Intact houseflies can be used to answer this question. Question 5: Does the wing surgery affect predation by jumping spiders? Zonosemata with their own wings reglued can be used to answer this question. When a jumping spider encounters a normal housefly, the spider typically attacks the fly. However, when the spider encounters a Zonosemata fly, the spider often retreats. We can measure the response of jumping spiders to flies from each group. When a jumping spider encounters an untreated Zonosemata (that is wing markings plus wing-waving fly), the spider often retreats. When a jumping spider encounters Zonosemata with own wings reglued (that is operation performed fly), the spider often retreats. When a jumping spider encounters Zonosemata with housefly wings (that is wing waving but no wing markings fly), the spider typically attacks the fly. When a jumping spider encounters a Housefly with Zonosemata wings (that is wing markings but no wing-waving fly), the spider often retreats. When a jumping spider encounters an untreated housefly (that is no wing markings, no wing-waving fly), the spider typically attacks the fly. Let's examine the results in light of our original hypothesis, which stated that Zonosemata vittigera flies mimic jumping spiders to deter predation by the spider. From these results, we can say that both wing markings and wing waving were important in causing the spiders to retreat. However, the sub-hypotheses that wing markings or wing waving alone would cause the spider to retreat were rejected.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 20m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
- 45. Nervous System55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
1. Introduction to Biology
Experimental Design
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