Investigating Cell Theory Image acquired from http discussions

Investigating Cell Theory Image acquired from http: //discussions. texasbowhunter. com/forums/showthread. php? t=112982

Objectives: Study how the scientific process influenced our understanding of how life originates. Investigate the idea of abiogenesis or spontaneous generation. Understand how theories are formed in science. Discuss the current cell theory.

Vocabulary Abiogenesis (Spontaneous Generation) - Living organisms can arise spontaneously from non-living matter Cell - a structure that contains all the material needed for life Life - the condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change preceding death. Theory - a well-substantiated explanation of some aspect of the natural world

Habits of the Mind Remaining Open to Continuous Learning Thinking Flexibly

Titan Creed Titans endeavor to recognize and pursue truth, beauty, and goodness.

Key Question: How does life originate? All civilizations have pondered this question.

Prior to science… How did people interpret the world? For thousands of years, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas. Conclusions were based on untested observations. The scientific method did not exist.

Definition: Abiogenesis or Spontaneous Generation Living organisms can arise spontaneously from living (not related) or non-living matter whenever conditions are favorable.

Observations of Ancient Egyptians: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. Along with the muddy soil, large numbers of frogs appeared that were not around in drier times. Conclusion: Frogs came from the mud of the Nile. Imaged acquired from http: //senr. osu. edu/about-us/news/transition

Observations of Ancient Civilizations Ancient China – Aphids spontaneously generate from bamboo India – Flies come from dirt and sweat Ancient Babylonia – Mud from canals produced worms

Greek Philosophers…. Aristotle - Developed the “theory” of spontaneous generation “Active principle” responsible for life Fleas came from sweat Mice came from garbage Flies and maggots came from dead/decaying meat Supported by Thales Democritus Plato Remained unchallenged until the Scientific Revolution of the 17 th century

Maggots came from rotting meat… Image acquired from http: //discussions. texasbowhunter. com/forums/showthread. php? t=112982

Caterpillars came from dew on cabbage leaves… Images acquired from http: //www. flickr. com/photos/lordv/2639277095/ and http: //www. wildaboutbritain. co. uk/forums/eggs-larvae-and-caterpillars/16340 -butterfly-eggs. html

Moths came from wool…

Early Scientific Experiments Jan Baptista van Helmont Early 1600’s - Belgian physician Found wheat grains in a sweaty shirt. After 21 days - the wheat grains were gone and mice were present. Concluded - sweat was the “active principle” that changed the wheat grains into mice. What was wrong with this experiment?

Early Scientific Experiments Francisco 1668 Redi - Italian physician Proposed that flies produce maggots Observed that after a few days, maggots appeared on meat after flies were present. Used the scientific method to question the validity of the “theory” of spontaneous generation. Concluded: Maggots came from eggs laid by flies.

Redi’s Experiment What is the control of this experiment? VIDEO: Redi's Experiment

Early Scientific Experiments Anton Van Leeuwenhoek - Father of Microscopy 1683 -Dutch Unlikely scientist No fortune; No higher education Started as an apprentice in a dry goods store (tradesmen) Magnifying glasses were used to count the threads in cloth. Inspired by the glasses used by drapers to inspect the quality of cloth Taught himself new methods for grinding/polishing tiny lenses of great curvature Gave magnifications up to 270 x diameters Lenses led to the building of his microscopes Considered the first practical microscopes Skill, diligence, an endless curiosity, and an open mind free of the scientific dogma of his day, allowed Leeuwenhoek to succeed in making some of the most important discoveries in the history of biology.

Anton Van Leeuwenhoek Gathered a water sample when he went boating. Noticed the water was cloudy. Placed a sample of the water under a microscope. The sample contained tiny living organisms. 1 st to see tiny organisms under a microscope. Named these organisms “animacules. ” For the next 200 years, scientists could not agree whether the “animacules” were alive or how they came to exist. What do you think these tiny living organisms were?

Anton Van Leeuwenhoek Video: The Hidden Life in Pond Water Image acquired from http: //www. britannica. com/EBchecked/media/110525/Microscope-made-by-Antonie-van-Leeuwenhoek Image acquired from http: //lensonleeuwenhoek. net/overview. htm

Early Scientific Experiment John mid Needham 1700’s - English scientist Used an experiment containing “animacules” to refute Redi’s work. Needham claimed that under the right conditions, spontaneous generation could occur.

Needham Experiment: Boiled broth in a flask for a few minutes; claimed to kill all the living things in it with heat. Sealed the flask. After several days he found organisms swarming in the broth. Conclusion: The “little animals” came from the broth.

Lorenzo Spallanzini • Late 1700’s - Italian scholar • Read about Needham’s work. • Believed Needham’s experiment was flawed. • Microorganisms in the air got in the flask between the boiling and sealing. • Substance not boiled long enough to kill the microbes. • Conducted a similar experiment in a partial vacuum. • No life was found in the sealed flask. Image acquired from http: //en. wikipedia. org/wiki/File: Spallanzani. jpg

Lorenzo Spallenzini Conclusion: Nonliving gravy did not produce living things. Supported the hypothesis that new organisms are only produced by existing organisms. Skeptics argued that this only proved that spontaneous generation needs air to function.

Louis Pasteur – Settled the argument • 1864 - French scientist • Designed a curved neck flask to conduct his experiment that remained open to the air; did not allow microorganisms to make their way through the neck into the flask. • One of science’s most famous experiments Image acquired from http: //www. biography. com/people/louis-pasteur-9434402

Pasteur’s Conclusion: • Broth in the broken flasks quickly became cloudy --a sign that it teemed with microbial life. • Broth in unbroken flasks - remained clear • Without the introduction of dust--on which microbes can travel--no life arose. • Louis Pasteur experiment refuted the notion of spontaneous generation. Video: Louis Pasteur - Biography Video: Redi and Pasteur's Experiments

Question to Ponder… Can spontaneous generation occur on Earth today?

What is a scientific theory? A well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses" Merriam-Webster's Medical Dictionary

What is a scientific theory? Theories accepted by the scientific community majority are generally strongly supported by many different lines of evidence-but theories may be modified or overturned if warranted by new evidence and perspectives. http: //undsci. berkeley. edu/article/howscienceworks_19

Theories are central to scientific thinking. Theories are overarching explanations that make sense of some aspect of nature, are based on evidence, allow scientists to make valid predictions, and have been tested in many ways. Theories are supported, modified, or replaced as new evidence appears. Theories give scientists frameworks within which to work.

Theories are central to scientific thinking. Major theories of science, such as the cell theory, gravitational theory, evolutionary theory, and particle theory, are all big ideas within which scientists test specific hypotheses. The strength of a theory depends on its supporting lines of evidence.

Key Question Based on the current definition of a scientific theory, would you consider spontaneous generation a “theory? ”

Cell Theory – History (19 th century) Compound microscope - highly advanced Series of discoveries provided basic information for cell theory 1831 - Robert Brown Discovered nucleus in cells of plants 1838 - Mathias Schleiden (German botanist) Observation - all plants were made up of cells 1839 - Theodlor Schwann Observation – all animals were made up of cells which were similar to plant cells.

Cell Theory - History Schleiden/Schwann formulated the “Cell Theory”. All organisms are made up of cells. The cell was considered a bag of thick dense substance containing a nucleus. Power/quality of microscopes improved Revealed sub cellular bodies inside the cell : “organelles”

Cell Theory - Current All living things are made up of cells. Cells are the basic units of life. Living cells can come only from other preexisting cells. Cells contain and pass on hereditary information during cell division. All cells are relatively the same in relation to chemical composition and metabolic activity.

Cell Theory Overview VIDEO: The Wacky History of Cell Theory Rap: Cell Theory

Works Cited Andre Brack. The Molecular Origins of Life: Assembling Pieces of the Puzzle. Cambridge University Press. March 1999. Levine, Russell and Chris Evers. The Slow Death of Spontaneous Generation (1668 -1859). 31 March 2009. Access Excellence. http: //www. accessexcellence. org/RC/AB/BC/Spontaneous_Generation. php. Web. Spontaneous Generation. 31 March 2009. Virginia University. http: //etext. virginia. edu/cgi-local/DHI/dhi. cgi? id=dv 4 -39. Web.