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CellsHow their
discovery led to the Cell
Theory
CellsHow their
discovery led to the Cell
Theory
HistoryCells 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
Leeuwenhoek
Studied pond water, sour milk, and semen
named moving organisms “animalcules”
scared people and caused a sensation
Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- pond water animalcules causing madness!
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.
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.
Definition of Cell
• A cell is the smallest unit that is capable of performing life functions.
• A cell is the basic unit of life.
Examples of CellsAmoeba Proteus Plant
Stem
Red Blood CellNerve
Cell
Bacteria
The Cell TheoryThe 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)
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.
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
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
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.
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.
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?
Francesco RediBorn 1626 in Italy
First to challenge the idea of spontaneous generation
Did not accept the common belief that flies magically appeared from rotting meat
Redi’s Experiment
IV=cover
DV=presence of flies
Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies
Redi’s Conclusions
Flies lay eggs, which grow into maggots, which metamorphose into flies
If flies can’t lay eggs, then no new flies can grow
Fly eggs
Objections to RediMany 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”
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
Lazzaro Spallanzani
Spallanzani’s Experiment
Flask 1: boiled broth, open
Flask 2: boiled broth, sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil
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.
Louis Pasteur1822. France
Supported that spontaneous generation is a myth
Invented pasteurization (sterilization by heat)
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.
The curved neck allows air in but traps bacteria-carrying dust and dirt
particles
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.
Pasteur is the father of modern microbiologysupported 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.
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
Cell Structure & Function
http://koning.ecsu.ctstateu.edu/cell/cell.html
Examples of Cells
Amoeba Proteus Plant
Stem
Red Blood CellNerve
Cell
Bacteria
Two Types of Cells
• Prokaryotic
• Eukaryotic
ProkaryoticDo not have structures surrounded by membranes
Few internal structures
One-celled organisms, Bacteria
http://library.thinkquest.org/C004535/prokaryotic_cells.html
EukaryoticContain organelles surrounded by membranes
Most living organisms
PlantAnimal
“Typical” Animal Cell
“Typical” Plant Cell
Cell Parts
Organelles
Surrounding the Cell
Cell Membrane
Outer membrane of cell that controls movement in and out of the cell
Double layer
http://library.thinkquest.org/12413/structures.html
Cell Wall
Most commonly found in plant cells & bacteria
Supports & protects cells
Inside the Cell
Nucleus
Directs cell activities
Separated from cytoplasm by nuclear membrane
Contains genetic material - DNA
Nuclear Membrane
Surrounds nucleus
Made of two layers
Openings allow material to enter and leave nucleus
Chromosomes
In nucleus
Made of DNA
Contain instructions for traits & characteristics
Nucleolus
Inside nucleus
Contains RNA to build proteins
Cytoplasm
Gel-like mixture
Surrounded by cell membrane
Contains hereditary material
Endoplasmic Reticulum
Moves materials around in cell
Smooth type: lacks ribosomes
Rough type (pictured): ribosomes embedded in surface
Ribosomes
Each cell contains thousands
Make proteins
Found on ribosomes & floating throughout the cell
MitochondriaProduces energy through chemical reactions – breaking down fats & carbohydrates
Controls level of water and other materials in cell
Recycles and decomposes proteins, fats, and carbohydrates
Chemical diagram of an ATP molecule.
Golgi Bodies
Protein 'packaging plant'
Move materials within the cell
Move materials out of the cell
LysosomeDigestive 'plant' for proteins, fats, and carbohydrates
Transports undigested material to cell membrane for removal
Cell breaks down if lysosome explodes
VacuolesMembrane-bound sacs for storage, digestion, and waste removal
Contains water solution
Help plants maintain shape
Chloroplast
Usually found in plant cells
Contains green chlorophyll
Where photosynthesis takes place
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