Science 10 – Unit C - BIOLOGY
Chapter 1 – The Microscope
C1.2 - Development of cell theory
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When science contradicts belief:
o sometimes, despite scientific evidence to the contrary, people find it hard to accept new
ideas
o as a result, scientific advancement is sometimes slowed
Galileo
o imprisoned in 1630s by the Catholic Church for claiming that
o the Church took exception to this idea because they believed that since God created
man,
o despite being correct, Galileo was forced to recount his findings and spent his last years
on house arrest
o October 31, 1992 – Pope John Paul II issued a papal pardon,
Spontaneous Generation
 another idea that was believed for hundreds of years despite scientific evidence to the contrary
 spontaneous generation is the belief that
 widely accepted until the 19th century
 people believed there was a life force that caused non-living things to “birth” living things
 two photos
o the first is the imprint of a fossilized plant in a rock
o the second is a moldy sandwich
o how do we explain these two photos?
o prior to the 19th century, people would have explained these two
situations differently
 the plant: they would assume
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the sandwich: a non-living thing, would give the mold
Francisco Redi
o set up an experiment to illustrate that maggots, (a living thing)
did not grow spontaneously out of raw meat (a non-living thing)
o set out two flasks
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o only the flask open to air (and flies) had evidence of maggots
o Redi thought this disproved spontaneous generation, but other scientists said
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John Needham
o performed another experiment, and claimed that
o boiled chicken broth (to kill bacteria)
o put it in a sealed flask
o found that
 likely because broth wasn’t heated
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Lazzaro Spallanzani
o repeated Needham’s experiment, but in a vacuum
o this removed
o no microorganisms appeared
o despite this evidence, Needham still maintained this only proved
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Louis Pasteur
o his experiment in 1864 was finally the decisive proof the scientific community needed
o Pasteur set up two flasks, each with the same meat broth
 he heated them both to sterilize them
 the flasks he used had bent necks, so that they were
 initially, neither broth became cloudy with microbial growth
o In experiment 1, Pasteur broke off the neck of the flask,
 dust now had access to flask 1, while it got trapped in the neck of flask 2
 over time, microorganisms
o this proved that microorganisms are not generated by the broth, but rather
Experimental variables
 whenever performing an experiment, a scientist must decided what he or she is testing for
o some variables will change from trial to trial,
o some variables will stay the same so the scientist knows that
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Manipulated variable
o the variable that
o in Pasteur’s experiment, the manipulated variable was
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Responding variable
o the responding variable is
o in Pasteur’s experiment, the responding variable was
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Controlled variables
o the controls are
o in Pasteur’s experiment, the controls were:
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Practice problems
o In each of the experiments described below, identify the manipulated, responding, and at
least two controlled variables:
 a science student wants to know if the amount of water given to a plant affects
how tall it will grow
 M:
R:
 C:
 a pharmaceutical company wants to know if a new drug is effective in treating
migraines
 M:
R:
 C:
 a car company wants to know if the type of brake pads in a car affects stopping
distance
 M:
R:
 C:
Cell theory
 Robert Brown
o with improvements in lens technology came a new understanding of the cell
o in 1833, identified the nucleus of the cell as
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Schleiden & Schwann
o made observations on plant and animal cells
o together, proposed that
o described cells as
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Rudolf Virchow
o expanded on Schleiden and Schwann’s theories on cells
o theorized that all cells arise only from pre-existing cells
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Summary of cell theory
o all living things are made up of one or more cells and
o all life functions take place in cells, making them
o all cells are produced from pre-existing cells
Homework: Check and Reflect page 252 #2-4
 Make a list of the scientists from sections C1.1 and 1.2 with one or two points on their
contribution to science