CELL THEORYCELL THEORY A theory resulting from many scientists’ A theory resulting from many scientists’

observationsobservations & & conclusionsconclusions

CELL THEORYCELL THEORY 1. The basic unit of life is the1. The basic unit of life is the cellcell. (. (HookeHooke)) In 1665, an English scientist In 1665, an English scientist

named named Robert HookeRobert Hooke made made an improved microscope and an improved microscope and viewed thin slices of viewed thin slices of cork cork viewing plant cell wallsviewing plant cell walls

Hooke named what he saw Hooke named what he saw "cells""cells"

Discovery of CellsDiscovery of Cells 1665- English Scientist, Robert Hooke, discovered cells 1665- English Scientist, Robert Hooke, discovered cells

while looking at a thin slice of cork.while looking at a thin slice of cork. He described the cells as tiny boxes or a honeycombHe described the cells as tiny boxes or a honeycomb He thought that cells only existed in plants and fungiHe thought that cells only existed in plants and fungi

Anton van LeuwenhoekAnton van Leuwenhoek 1673- Used a handmade microscope to observe pond 1673- Used a handmade microscope to observe pond

scum & discovered single-celled organismsscum & discovered single-celled organisms He called them “animalcules”He called them “animalcules”

He also observed blood cells from fish, birds, frogs, He also observed blood cells from fish, birds, frogs, dogs, and humansdogs, and humans

Therefore, it was known that cells are found in animals Therefore, it was known that cells are found in animals as well as plantsas well as plants

Development of Cell TheoryDevelopment of Cell Theory 1838- German Botanist, Matthias Schleiden, 1838- German Botanist, Matthias Schleiden,

concluded that all plant parts are made of cellsconcluded that all plant parts are made of cells 1839- German physiologist, Theodor Schwann, who 1839- German physiologist, Theodor Schwann, who

was a close friend of Schleiden, stated that all was a close friend of Schleiden, stated that all animal tissues are composed of cells.animal tissues are composed of cells.

Development of Cell TheoryDevelopment of Cell Theory 1858- Rudolf Virchow, German physician, after 1858- Rudolf Virchow, German physician, after

extensive study of cellular pathology, concluded extensive study of cellular pathology, concluded that cells must arise from preexisting cells.that cells must arise from preexisting cells.

150-200 Year Gap???150-200 Year Gap??? Between the Hooke/Leuwenhoek discoveries Between the Hooke/Leuwenhoek discoveries

and the mid 19and the mid 19thth century, very little cell century, very little cell advancements were made.advancements were made.

This is probably due to the widely accepted, This is probably due to the widely accepted, traditional belief in Spontaneous Generation.traditional belief in Spontaneous Generation.

Examples: Examples: -Mice from dirty clothes/corn husks-Mice from dirty clothes/corn husks-Maggots from rotting meat-Maggots from rotting meat

1919thth Century Advancement Century Advancement Much doubt existed around Spontaneous GenerationMuch doubt existed around Spontaneous Generation Conclusively disproved by Louis PasteurConclusively disproved by Louis Pasteur

Pasteur: Ummm, I don’t think so!!!

+

=?

The Cell Theory CompleteThe Cell Theory Complete The 3 Basic Components of the Cell Theory The 3 Basic Components of the Cell Theory

were now complete:were now complete: 1. All organisms are composed of one or more cells. 1. All organisms are composed of one or more cells.

(Schleiden & Schwann)(1838-39)(Schleiden & Schwann)(1838-39) 2. The cell is the basic unit of life in all living things. 2. The cell is the basic unit of life in all living things.

(Schleiden & Schwann)(1838-39)(Schleiden & Schwann)(1838-39) 3. All cells are produced by the division of 3. All cells are produced by the division of

preexisting cells. (Virchow)(1858)preexisting cells. (Virchow)(1858)

Functions of lifeFunctions of life All organisms carryout all the functions of All organisms carryout all the functions of

life likelife like MetabolismMetabolism GrowthGrowth ReproductionReproduction ResponseResponse HomeostasisHomeostasis nutritionnutrition

VirusesVirusesViruses are not considered to be living Viruses are not considered to be living things since they cannot carry out the things since they cannot carry out the

functions of life on their ownfunctions of life on their own

Cells and sizes.Cells and sizes.

Some Random Cell FactsSome Random Cell Facts

The average human being is composed of The average human being is composed of around 100 Trillion individual cells!!!around 100 Trillion individual cells!!!

It would take as many as 50 cells to cover It would take as many as 50 cells to cover the area of a dot on the letter “the area of a dot on the letter “ ii””

WOW!!!WOW!!!

MagnificationMagnification Light microscopes upto 2000 *Light microscopes upto 2000 * Electron microscopes over 100000*Electron microscopes over 100000* To know the actual size of a specimen To know the actual size of a specimen

scale bars are used with a micrographscale bars are used with a micrograph

Cell SizeCell Size

Most cells are relatively small because as Most cells are relatively small because as size increases, volume increases much size increases, volume increases much more rapidly.more rapidly. longer diffusion timelonger diffusion time