1. Cells
How their
discovery led to
the Cell Theory
2.
3. History
Cells were unknown until the
discovery of microscopes in the
1650’s
two scientists working
independently built the first
microscopes
Anton von Leeuwenhoek in
Holland
Robert Hooke in England
4. Leeuwenhoek
Studied pond water, sour milk,
and semen
named moving organisms
“animalcules”
scared people and caused a
sensation
6. and...
Human sperm cells
contain tiny human
beings!
Today we can look
back and think
“crazy,” but at the
time people took these
ideas very seriously.
7. Hooke
Studied cork - a kind
of tree bark
named the structures
he saw “cells” because
they reminded him of
the small rooms
monks slept in.
8. Definition of Cell
• A cell is the smallest unit that is
capable of performing life
functions.
• A cell is the basic unit of life.
9. Examples of Cells
Amoeba
Proteus Plant
Stem
Bacteria
Red
Blood Cell
Nerve
Cell
10. The Cell Theory
The cell theory has three parts:
All living things contain at least one
cell
Cells are the smallest working units
of all living things.
Cells can only come from pre-existing
cells through cell division (meiosis)
11. The cell theory-a closer look
All living things contain at least one cell
Many scientists working after Hooke
and Leeuwenhoek observed different
plants and animals
Each of them noted that no matter
what they observed, if it was alive it
had cells.
12. Cells are the smallest working units of
all living things.
Scientists (Theodor Schawnn
&Matthias Schleiden) quickly
realized that when cells were
dissected or broken open they died
This meant that whatever “life” is, it
is something that happens inside cells
13. Cells can only come from pre-existing
cells through cell division
does not answer the question of where
the first cell came from or how it
came to be.
has not been disproved yet- no
scientist has ever built a living cell
from nonliving organic molecules
14. Spontaneous Generation
From pre-historic times to about 1850,
most people believed that under the right
conditions, living things could
spontaneously appear from non-living
material.
15. People throughout the
Middle Ages believed
that mice could be
“created”
spontaneously by
putting grain in dark,
quiet place and leaving
it for a few weeks.
16. The discovery of
cells only confused
people more- If
cells are alive,
then where do
they come from?
Can these
almost invisible
things appear
spontaneously
from the air?
17. Francesco Redi
Born 1626 in Italy
First to challenge the
idea of spontaneous
generation
Did not accept the
common belief that
flies magically
appeared from rotting
meat
18. Redi’s Experiment
IV=cover
DV=presence of flies
Hypothesis: If a jar
containing rotting
meat is covered, then
it will produce no
flies
19. Redi’s Conclusions
Flies lay eggs, which
grow into maggots,
which metamorphose
into flies
Fly eggs
If flies can’t lay eggs,
then no new flies can
grow
20. Objections to Redi
Many people rejected Redi’s claim that
flies do not spontaneously generate
Their reasoning:
“sealing the jar closed prevented a
magical essence from entering the
rotting meat and brining it to life”
“Scientists seek only to challenge belief
systems and stir things up”
21. Lazzaro Spallanzani
1729. Italian
Believed microbes that spoil food
come from the air and can be killed
by boiling
IV= air, DV=food spoilage
Hypothesis: If air is allowed to
reach food, then microbes will get in
and cause it to spoil
22. Spallanzani’s Experiment
Flask 1: boiled broth, open
Flask 2: boiled broth, sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil
23. Objections to Spallanzani
Sealing the flask shut
blocked the entrance of a
magical life force in the air
from getting to the broth.
Since few people had seen
these microbes, few people
believed him.
25. Pasteur’s Experiment
An improvement on Spallanzani’s work
Used special “swan-neck flasks” that allowed
air in but kept bacteria out
IV= bacteria, DV=spoiling broth
Hypothesis; If boiled broth is kept free of
bacteria, then it will not spoil even if air can
reach it.
26. The curved neck allows air in but traps
bacteria-carrying dust and dirt particles
27. Spontaneous generation is
dead!
Redi didn’t believe in it, and did an
experiment using flies
Spallanzani didn’t believe in it, and
experimented with broth
Pasteur disproved it conclusively with
his open-air yet spoilage free flasks.
28. Pasteur is the father of
modern microbiology
supported the last part of the cell theory:
cells only come from pre-existing cells
identified yeasts as the microbes that
change grape juice into wine
showed that heat can be used to sterilize
foods and preserve them in sealed glass
containers, and later cans.
29. The cell theory is one of the
most important theories in
biology.
All living things contain at least one cell
Cells are the smallest living units of matter
Cells can only come from pre-existing cells
30. Cell Structure & Function
http://koning.ecsu.ctstateu.edu/cell/cell.html
31. Examples of Cells
Amoeba
Proteus Plant
Stem
Bacteria
Red
Blood Cell
Nerve
Cell
33. Prokaryotic
Do not have
structures
surrounded by
membranes
Few internal
structures
One-celled
organisms,
Bacteria
http://library.thinkquest.org/C004535/prokaryotic_cells.html
34. Eukaryotic
Contain organelles surrounded by
membranes
Most living organisms Animal
Plant
40. Cell Membrane
Outer membrane of cell
that controls movement
in and out of the cell
Double layer
http://library.thinkquest.org/12413/structures.html
41.
42.
43. Cell Wall
Most commonly
found in plant cells &
bacteria
Supports & protects
cells
52. Mitochondria
Produces energy through
chemical reactions –
breaking down fats &
carbohydrates
Controls level of water
and other materials in cell
Recycles and decomposes
proteins, fats, and
carbohydrates
56. Lysosome
Digestive 'plant' for
proteins, fats, and
carbohydrates
Transports undigested
material to cell
membrane for removal
Cell breaks down if
lysosome explodes
