Transcript File - Mr. Downing Science 10

Science 10 – Unit C
BIOLOGY
Chapter 1 – The Microscope
C1.2
Development of cell theory
Brain cells of a rat.
When science contradicts belief:
sometimes, despite scientific evidence to the
contrary, people find it hard to accept new ideas
– as a result, scientific advancement is sometimes slowed
Galileo
– imprisoned in 1630s by the Catholic Church for
claiming that the Earth revolved around the Sun
– the Church took exception to this idea because they
believed that since God created man, he should be at
the centre of the Universe
– despite being correct, Galileo was forced to recount his
findings and spent his last years on house arrest
– October 31, 1992 – Pope John Paul II issued a papal
pardon, 350 years after Galileo’s death
Spontaneous Generation
another idea that was believed for
hundreds of years despite scientific
evidence to the contrary
spontaneous generation is the belief that
living things can emerge from non-living
matter
– widely accepted until the 19th century
– people believed there was a life force that
caused non-living things to “birth” living things
Spontaneous Generation
To the left we have two photos
– the first is the imprint of a fossilized plant in a
rock
– the second is a moldy sandwich
How do we explain these two photos?
– the plant:
trapped between the rock and the layers of dirt
and sediment above it
as it decomposed, it wore out a pattern in the rock
– the sandwich:
microscopic spores of fungus landed on the bread
over time, the fungus spread across the surface of
the bread, giving it the moldy appearance
Spontaneous Generation
prior to the 19th century,
people would have explained
these two situations differently
– the plant:
they would assume the plant had
grown out of the rock
– the sandwich:
the sandwich, a non-living thing,
would give the mold a life force,
allowing it to grow
Francisco Redi
set up an experiment to illustrate that maggots,
(a living thing) did not grow spontaneously out
of raw meat (a non-living thing)
set out two flasks
– one with access to air
– one without access to air
only the flask open to air (and flies) had
evidence of maggots
Redi thought this disproved spontaneous
generation, but other scientists said it proved
that air was a necessary ingredient in life force
John Needham
performed another experiment, and
claimed that it proved the existence of life
forces
– boiled chicken broth (to kill bacteria)
– put it in a sealed flask
– found that microorganisms still appeared
likely because broth wasn’t heated for long enough
or at a high enough temperature
Lazzaro Spallanzani
repeated Needham’s
experiment, but in a vacuum
– this removed all the air from
the flask before it was sealed
– no microorganisms appeared
despite this evidence,
Needham still maintained this
only proved air was an
ingredient in life force
Louis Pasteur
his experiment in 1864 was finally
the decisive proof the scientific
community needed to reject
spontaneous generation once and
for all
Louis Pasteur
Pasteur set up two flasks, each with the
same meat broth
– he heated them both to sterilize them and
remove the bacteria
– the flasks he used had bent necks, so that they
were open to the air but protected from dust
– initially, neither broth became cloudy with
microbial growth
In experiment 1,
Pasteur broke off
the neck of the
flask, giving it
access to air
In experiment 2, he
left the neck intact
dust now had access to
flask 1, while it got
trapped in the neck of
flask 2
over time,
microorganisms
appeared in flask 1, but
not in flask 2
this proved that
microorganisms are not
generated by the broth,
but rather carried in the
air, and simply too
small to see
Experimental variables
whenever performing an experiment, a
scientist must decided what he or she is
testing for
– some variables will change from trial to trial,
and the results analyzed
– some variables will stay the same so the
scientist knows that these variables are not the
cause of any differences between trials
Manipulated variable
the variable that is altered between trials
in Pasteur’s experiment, the manipulated
variable was whether the flask’s neck was
broken or left intact
Responding variable
the responding variable is the results of the
changes made
in Pasteur’s experiment, the responding
variable was the presence of microbial
growth
Controlled variables
the controls are all the things that could have
been changed, but were deliberately kept
constant
in Pasteur’s experiment, the controls were:
–
–
–
–
–
the temperature and duration of heating
the shape and size of flasks before they were broken
the type of broth
the amount of broth
etc.
Variables - Practice problems
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
– a pharmaceutical company wants to know if a
new drug is effective in treating migraines
– a car company wants to know if the type of
brake pads in a car affects stopping distance
Robert Brown
with improvements in lens technology
came a new understanding of the cell
in 1833, identified the nucleus of the cell as
being responsible for controlling cell
function
Schleiden & Schwann
made observations on plant and animal
cells
together, proposed that all plant and
animals are composed of cells
described cells as the basic unit of life for
all organisms
Rudolf Virchow
Expanded on Schleiden and Schwann’s
theories on cells
theorized that all cells arise only from preexisting cells
Summary of cell theory
The three points of cell theory are:
1. all living things are made up of one or more
cells and the materials produced by these
cells
2. all life functions take place in cells, making
them the smallest unit of life
3. all cells are produced from pre-existing cells
through the process of cell division, also
called mitosis
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