Cell Theory

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 February 17, 2019

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 micrometres (millionth of a metre) Size: 100 - 350 micrometres Size: 100 - 350 micrometres February 17, 2019

Some Multicellular Life Forms: Grass – a common plant Cow – a common creature that eats grass Human – a life form that may eat a cow February 17, 2019

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! February 17, 2019

We Are Not Alone! February 17, 2019

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) February 17, 2019

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 i.e.: Bacteria February 17, 2019

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 February 17, 2019

Prokaryotes vs. Eukaryotes Notice the difference in complexity! February 17, 2019

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 February 17, 2019

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 February 17, 2019

Spontaneous Generation???? Next 150 - 200 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 February 17, 2019

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? February 17, 2019

Development of Cell Theory – 1800’s 1833 – Robert Brown Observed the nucleus in the epidermis of an orchid February 17, 2019

Schleiden and Schwann 1838 - 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. February 17, 2019

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” February 17, 2019

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 February 17, 2019

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Sperm and egg cell February 17, 2019

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Plant cells – shown: early anaphase February 17, 2019

Frog cell anaphase February 17, 2019

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