CELLS The Smallest Units Defined as Life

Wall Walk Aristotle Aristotle Gregorio Redi Gregorio Redi Robert Hooke Robert Hooke Anton van Leeuwenhoek Anton van Leeuwenhoek Lazzaro Spallanzani Lazzaro Spallanzani Louis Pasteur Louis Pasteur Jean-Baptiste de Lamark Jean-Baptiste de Lamark Matthias Schleiden Matthias Schleiden Theoror Schwann Theoror Schwann Rudolph Virchow Rudolph Virchow What is the Cell Theory?

Aristotle B.C. “On the Generation of Animals” Discussed fundamental questions of life: How does reproduction occur? How does development occur? How does heredity take place? “ … within each germ springs from a definite parent and gives rise to a predictable progeny. And thus it is the germ that is the ruling influence and fabricator of the offspring."

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.

Francesco Redi 1668 Born 1626 in Italy Born 1626 in Italy First to challenge the idea of spontaneous generation First to challenge the idea of spontaneous generation Did not accept the common belief that flies magically appeared from rotting meat Did not accept the common belief that flies magically appeared from rotting meat 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 Flies lay eggs, which grow into maggots, which metamorphose into flies If flies can’t lay eggs, then no new flies can grow If flies can’t lay eggs, then no new flies can grow

We Object! Many people rejected Redi’s claim that flies do not spontaneously generate Many people rejected Redi’s claim that flies do not spontaneously generate Their reasoning: Their reasoning: “sealing the jar closed prevented a magical essence from entering the rotting meat and brining it to life” “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” “Scientists seek only to challenge belief systems and stir things up”

THE MICROSCOPE This instrument opened up new doors in the field of biology; Galileo designed a compound microscope

1665-Robert Hooke viewed thin slices of cork tree under a crude microscope and observed tiny hollow boxes. He called these boxes cells. viewed thin slices of cork tree under a crude microscope and observed tiny hollow boxes. He called these boxes cells. Image Credit Cork cellsCork cells © 2010 Paul Billiet ODWSODWS

1674- Anton van Leeuwenhoek observed tiny living organisms in drops of pond water Anton van Leeuwenhoek observed tiny living organisms in drops of pond water. Made over 250 microscopes Made over 250 microscopes Caused a sensation and scared people! Caused a sensation and scared people!

Lazzaro Spallanzani Italian Italian Believed microbes that spoil food come from the air and can be killed by boiling Believed microbes that spoil food come from the air and can be killed by boiling Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

Spallanzani’s Experiment Flask 1: boiled broth, open Flask 2: boiled broth, sealed shut Results Flask 1 spoiled Flask 2 did not spoil

Louis Pasteur 1862 Anti-spontaneous generation experiments: Anti-spontaneous generation experiments: Improved on Spallanzani’s work Improved on Spallanzani’s work Pasteur definitively demonstrated that microorganisms are present in air but not created by air. This was critical for refutation of the concept of spontaneous generation and the for development of germ theory of disease. Pasteur definitively demonstrated that microorganisms are present in air but not created by air. This was critical for refutation of the concept of spontaneous generation and the for development of germ theory of disease. microorganismsspontaneous generationgerm theory of diseasemicroorganismsspontaneous generationgerm theory of disease

JEAN-BAPTISTE DE LAMARCK The majority of this Frenchman's work dealt with animal classification and evolution. He is credited with taking steps towards the creation of the cell theory with this saying: "Every step which Nature takes when making her direct creations consists in organizing into cellular tissue the minute masses of viscous or mucous substances that she finds at her disposal under favorable circumstances

History of the Cell Theory Matthias Schleiden concludes that all plants are made up of cells Matthias Schleiden concludes that all plants are made up of cells.

History of the Cell Theory 1839-Theodor Schwann concludes that all animals are made up of cells Theodor Schwann concludes that all animals are made up of cells. Created the term Cell Created the term CellTheory

History of the Cell Theory 1855-Rudolph Virchow completes the cell theory by proposing all cells come from existing cells Rudolph Virchow completes the cell theory by proposing all cells come from existing cells. Demonstrated that the Demonstrated that the Cell Theory applies to diseased tissues as well

The Cell Theory: All organisms are composed of one or more cells All organisms are composed of one or more cells Evidence? Evidence? The cell is the basic unit of organization for the organism The cell is the basic unit of organization for the organism All cells come from pre- existing cells All cells come from pre- existing cells

Technology Connections Light Microscope 1600’s Light Microscope 1600’s Differential Centrifugation – 1930s Differential Centrifugation – 1930s Procedure to separate organelles from whole cells Procedure to separate organelles from whole cells Separate nucleus from cytoplasm Separate nucleus from cytoplasm Transmission Electron Microscope Transmission Electron Microscope A beam of electrons instead of light is passed through an ultra thin specimen; those that pass through onto photographic plates A beam of electrons instead of light is passed through an ultra thin specimen; those that pass through onto photographic plates Scanning Electron Microscope Forms a 3D image of the specimen Forms a 3D image of the specimen

Two basic cell types: Prokaryotic & Eukayotic Prokaryotic cells Earliest cells Earliest cells Lack membrane bound organelles Lack membrane bound organelles No nucleus No nucleus No mitochondria No mitochondria Have membrane, cytoplasm, free DNA, ribosomes Have membrane, cytoplasm, free DNA, ribosomes

Prokayrotic cells: Bacteria

May have evolved from Prokaryotic cell Have a nucleus that holds the DNA inside a membrane Have mitochondria Also have cell membrane & cytoplasm Eukaryotic cells:

What are Organelles? Specific structures in the cytoplasm of the cell Specific structures in the cytoplasm of the cell Perform specific functions for the cell Perform specific functions for the cell Organelles found only in plants include Organelles found only in plants include Cell walls Cell walls Chloroplasts Chloroplasts

Organelle found only in Animal Cells Centrioles Centrioles