1. Cell Theory
Biology 2

2. Introduction Living organisms are made up of CELLS
Living organisms can be made up of one cell or many hundreds of millions of cells
Unicellular – life forms consist of only one cell
Multicellular – life forms are made of many cells
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3. Some Unicellular Life Forms:
E. Coli – a mostly friendly bacteria that lives in our gut
Paramecium – a pond water creature that eats bacteria
Amoeba – a pond water predator that may eat paramecium
Size: 2 micrometers (millionth of a metre)
Size: micrometers
Size: micrometers
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4. Some Multicellular Life Forms:
Grass – a common plant Cow – a common creature that eats grass Human – a life form that may eat a cow
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5. Humans & Cells Made of trillions of cells Of those trillions there are
only about 200 different varieties
For example: brain cell, muscle cell & red blood cell
All humans began as one cell that grew & divided into trillions!
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6. We Are Not Alone!
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7. We Are Not Alone! Microorganisms live all over and inside our body!
Skin (surface & deep layers)
Saliva
Intestine
Stomach
Eyes, nose & ears
The number of human cells (trillions) are OUTNUMBERED by the number of bacteria, fungi & other microorganisms by at least a factor of 10 : 1 !!
(For every 1 human cell, we have 10 microorganisms living with us)
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8. Two Types of Cells - 1. Prokaryotic Cells
Evolutionarily ancient (3.8 billion years ago)
first cells on earth & only life form for billions of years before more complex cells came along
Have a membrane around its outside
outer boundary keeping insides in
No membrane around nucleus
genetic material floats around cell
“pro” = before, “karyon” = nucleus
Most often unicellular organisms
ie: Bacteria
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9. Types of Cells - 2. Eukaryotes
More complex cells – evolved from prokaryotic ancestor
Outer membrane (like prokaryotes)
Double-walled membrane around genetic material (DNA) = “nucleus”
“Eu” = true, “karyon” = nucleus
Membranes also surround internal cell sections of the cell = “organelles”
Involved in metabolism & energy conservation of energy within the cell
IE Mitochondria, Chloroplast, Golgi Apparatus
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10. Prokaryotes vs. Eukaryotes
Notice the difference in complexity!
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11. Discovery of Cells – Robert Hooke
1665 – English scientist, Robert Hooke, discovered cells while looking through one of the first microscopes Looked at a thin slice of cork and described what he saw as “tiny boxes or honeycombs” Named the boxes “cells” as they reminded him of the cells in monasteries Thought cells only existed in plants
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12. Anton van Leuwenhoek 1673 - Anton van Leuwenhoek used a
handmade microscope to observe
pond scum & discovered
single-celled organisms
He called them “animalcules”
He also observed blood cells from fish, birds, frogs, dogs, and humans
Therefore, it was known that cells are
found in animals as well as plants
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13. Spontaneous Generation????
Next years - Very little research on cells because widely accepted view of life was maintained by the church, which frowned on modern science
Their theory was based on observations such as…
Dead logs were the source of mushrooms
Rotting meat was the source of flies
Mouldy hay was the source of mice
Spontaneous Generation – living organisms arose from non-living objects
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14. How would you disprove Spontaneous Generation?
Many scientists were sceptical of Spontaneous Generation & set about to understand how organisms come into existence (through the scientific method!)
A jar of rotting meat
People used to believe that flies came from the rotting meat
How would you prove that flies were not a by-product of the rotting meat?
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15. Development of Cell Theory – 1800’s
1833 – Robert Brown
Observed the nucleus in the epidermis of an orchid
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16. Schleiden and Schwann
Matthias Schleiden, a German professor of botany, conclusively identified the first plant cells and concluded that all parts of a plant is made of cells
1839 – Theodor Schwann, a German physiologist, who was a close friend of Schleiden, stated that all animal tissues are composed of cells.
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17. Rudolf Virchow
1855 – Rudolf Virchow, German physician, now known as the father of modern pathology
Discovered that all disease results as an injury to the cell
Proved that cells arise from other cells, not from non-living matter
“Omnis cellula e cellula”
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18. Current Microscopes Scanning Electron Microscopes (SEM)
Bombards the object with a high-energy beam of electrons
Electrons bounce off the atoms of the object and make a picture
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20. Sperm and egg cell
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22. Plant cells – shown: early anaphase
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23. Frog cell anaphase
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