The Cell TheoryThe Cell Theory

The Cell TheoryThe Cell Theory

The The CELL THEORY,CELL THEORY, or cell or cell doctrine, states that all doctrine, states that all organisms are composed of organisms are composed of similar units of organization, similar units of organization, called cells.called cells.

History Leading up to Cell History Leading up to Cell TheoryTheory

1.1. First compound microscope First compound microscope developeddeveloped

Zacharias Jansen, of Middleburg, Zacharias Jansen, of Middleburg, Holland, around the year 1595.Holland, around the year 1595.

History Leading up to Cell History Leading up to Cell TheoryTheory

2.2. Robert HookeRobert Hooke English English

ScientistScientist Observed Observed

cells in corkcells in cork Approx. Approx.

16631663

History Leading up to Cell History Leading up to Cell TheoryTheory

3.3. Antony van Antony van LeeuwenhoekLeeuwenhoek

First to observe First to observe bacteria and bacteria and protozoaprotozoa

Called Called “animacules”“animacules”

Approx. 1673Approx. 1673

Development of Cell TheoryDevelopment of Cell Theory

1.1. Robert BrownRobert Brown British British

botanistbotanist Discovered Discovered

the nucleus of the nucleus of a cella cell

18331833

Development of Cell TheoryDevelopment of Cell Theory

2.2. Theodor Theodor SchwannSchwann German German

zoologistzoologist Described Described

animal cells animal cells with nucleuswith nucleus

18381838

Development of Cell TheoryDevelopment of Cell Theory

3.3. Matthias Matthias SchleidenSchleiden German botanistGerman botanist Described plant Described plant

cells with a cells with a nucleusnucleus

18381838

Development of Cell TheoryDevelopment of Cell Theory

4.4. Rudolf VirchowRudolf Virchow German doctorGerman doctor Stated “every Stated “every

cell originates cell originates from another from another cell”.cell”.

About 1855About 1855

Tenants of Modern Cell Tenants of Modern Cell TheoryTheory

1.1. All known living things are made up All known living things are made up of cells.of cells.

2.2. The cell is structural & functional The cell is structural & functional unit of all living things.unit of all living things.

3.3. All cells come from pre-existing cells All cells come from pre-existing cells by division. by division.

Tenants of Modern Cell Tenants of Modern Cell TheoryTheory

4.4. Cells contains hereditary Cells contains hereditary information which is passed from information which is passed from cell to cell during cell division.cell to cell during cell division.

5.5. All cells are basically the same in All cells are basically the same in chemical composition.chemical composition.

6.6. All energy flow (metabolismAll energy flow (metabolism & & biochemistry) of life occurs within biochemistry) of life occurs within cells.   cells.  

Historical Problem with the Historical Problem with the Cell TheoryCell Theory

Flew in the face of current beliefFlew in the face of current belief Then, current belief was life Then, current belief was life

originated from non-livingoriginated from non-living Known as Known as Spontaneous Spontaneous

GenerationGeneration Disproved by Louis PasteurDisproved by Louis Pasteur

Pasteur’s WorkPasteur’s Work

Nutrient broths were heated and Nutrient broths were heated and sterilized in a flask with a straight sterilized in a flask with a straight neck and a curved neck.neck and a curved neck.

Pasteur’s WorkPasteur’s Work

1.1. Step 1 of his procedureStep 1 of his procedure As his control, straight-neck flaskAs his control, straight-neck flask Allowed bacteria to growAllowed bacteria to grow

Pasteur’s WorkPasteur’s Work

2.2. Step 2 of his procedureStep 2 of his procedure S-shaped necks. S-shaped necks.

With such necks bacteria could With such necks bacteria could not enternot enter

Therefore no bacteria grew.Therefore no bacteria grew.

Pasteur’s WorkPasteur’s Work

Straight-neck, bacteriaStraight-neck, bacteriaS-shaped neck, no bacteriaS-shaped neck, no bacteria

So, based on his observations, So, based on his observations, what can you conclude?what can you conclude?

General ObservationsGeneral Observations

1. All cells posess:1. All cells posess: Cell membraneCell membrane CytoplasmCytoplasm RibosomesRibosomes Hereditary Information Hereditary Information

(DNA)(DNA)

General ObservationsGeneral Observations2. Prokaryotes2. Prokaryotes

Single celledSingle celled Genetic material Genetic material

is a single, is a single, circular strandcircular strand

No nucleusNo nucleus No membrane No membrane

bound bound organellesorganelles

3. Eukaryotes3. Eukaryotes Began as single-Began as single-

celledcelled Genetic material Genetic material

– many, strings– many, strings Has a nucleusHas a nucleus Membrane Membrane

bound bound organellesorganelles

Became multi-Became multi-celledcelled

General ObservationsGeneral Observations

4. Why are cells so small?4. Why are cells so small? Exchange sufficient amount of Exchange sufficient amount of

materialmaterial Surface area to volume ratioSurface area to volume ratio