1. Science 10 – Unit C BIOLOGY
Chapter 1 – The Microscope

2. C1.2 Development of cell theory
Brain cells of a rat.

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Louis Pasteur
his experiment in 1864 was finally the decisive proof the scientific community needed to reject spontaneous generation once and for all

11. 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

12. In experiment 1, Pasteur broke off the neck of the flask, giving it access to air
In experiment 2, he left the neck intact

13. 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

14. 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

15. 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

16. 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

17. 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.

18. 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

19. 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

20. 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

21. Rudolf Virchow Expanded on Schleiden and Schwann’s theories on cells
theorized that all cells arise only from pre-existing cells

22. Summary of cell theory The three points of cell theory are:
all living things are made up of one or more cells and the materials produced by these cells
all life functions take place in cells, making them the smallest unit of life
all cells are produced from pre-existing cells through the process of cell division, also called mitosis

23. 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