The Development of the Cell Theory Cell Biology Prepared by: A. Abougabal

The Development of the

Cell Theory

Cell Biology

Prepared by: A. Abougabal

Ancient Times• Ancient peoples are

always on the look-out for ways that organisms can be used by them.

• Some civilizations support “great thinkers” and philosophers, but they rarely base their thoughts on observation or experiments.

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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory

334 B.C.E - Aristotle

• Greek philosopher, Aristotle, begins to observe nature.

• He classifies all known organisms as either a Plant or and Animal.

• He writes that living things can arise spontaneously from non-living matter.

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1268 – 1st Eyeglasses

• Roger Bacon, an English friar makes reference to a pair of eye glasses.

• This means that glass is being developed and used in a way that makes it easier to see small things.

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1590 – 1st Microscope

• Zacharias Janssen, a Dutch eyeglass maker, makes the 1st microscope by placing two lenses on top of one another to make extra-large images.

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1600’s

• People start to question the origins of life.

• Many begin to suggest that life can only come from other forms of life rather than through spontaneous generation (as was suggested by Aristotle). This only took about 2000 years!

• William Harvey says that maggots do not come from the meat itself but from tiny eggs too small to be scene.

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William HarveyEnglish Physician

1578-1657

Cell Theory and the Scientists Who Helped

Shape It

• Anton van Leeuwenhoek (1632-1723) reports being able to see tiny beasties (0.002 mm) using a simple single-lens microscope.

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1674 – 1st Microscopic Beasties Seen!

He is known as the

“Father of microscopy.”

Anton van Leeuwenhoek

he documented unicellular organisms based on observations of protozoa [1673] and bacteria

[1683]

Robert Hooke• Born: July 18, 1635

• Died: March 3, 1703

• Wrote and published “Micrographia”

• Known as the

“English Father of

microscopy”http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Hooke.html

Robert HookeContributions:– [1665] He observed

pieces of cork from the bark of a cork tree under the microscope.

– His observations led him to coin the word “cell.” -“Cell” means little rooms in Latin

http://www.learner.org/channel/courses/essential/life/session1/closer1.html

1667 – Species Defined

• John Ray (1627-1705) defines a “species” as a set of individuals that can reproduce their own kind.

• The beginning of the end of spontaneous generation!

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1578-1657

• Francesco Redi (1626-1697) conducts experiments to prove that maggots do not appear in meat if flies cannot land on it!

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1578-1657

1668 – 1st Experiments about origins of maggots

• Microscope claimed to be an instrument of evil when a prominent person was horrified by the sight of a magnified flea!

• Scientists begin to doubt spontaneous generation, but the common people still believe in it!

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1700’s

• Microscopes become sturdier and easier to use.

• Flaws in glass production still causes images to be blurry and have coloured halos.

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1770 – Advancement of microscopes

• Jane Haldimand (1769-1858) writes textbooks for young people to learn about science.

• Terms such as

“cell”, “cellular system” and “Cellular tissue” appear in the book.

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1809 – 1st Science Texts for Students

• Francois Vincent Raspail (1794-1878) wrote a book called (translated from Latin)

“Every cell is derived from a pre-existing cell”.This again puts to rest the idea of spontaneous generation.

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1825 – Book “Cells from Cells”

• Biology is becoming an important science and the body of knowledge is growing, especially since the improvement of microscopes.

• Scientists begin to study the cell extensively!

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1830 – Cells are studied

• Robert Brown (1773-1858) is the 1st to consider the nucleus as a regular part of a living cell.

• The nucleus is still hard to see though without the invention of the electric light for his microscope.

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1831 – Nucleus of Cell Found

• Matthias Jacob Schleiden (1804-1881) makes the claim “All plants are made of cells”.

• Cells are alive!

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1838 – Plant cells!

• Theodor Schwann (1810-1882) makes the claim “All animals are made of cells”.

• “All living things are made of cells”

• Cells are the basic building blocks of life!

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1839 – Animal cells!

• Alexander Carl Heinrich Braun (1805-1877) makes the claim:

“The cell is the basic unit of life”.

• Cells are made of protoplasm enveloped by a flexible membrane.

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1845 – Cell Basic Unit of Life

• Louis Pasteur (1822-1895)

• conducts a series of experiments that once and for all put to rest the idea of spontaneous generation and concluding that living organisms do not arise from non-living matter.

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1860’s, The end of the “Spontaneous Generation” debate

Who came up with the theory?

• Major Contributors:

• Matthias Schleiden• Theodor Schwann• Rudolph Virchow

1-Rudolph Virchow

• German pathologist

• He is known as the

“Father of Pathology.”

Born: October 13, 1821Died: September 5, 1902

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Rudolph wirchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing

cells [1855] All cells come from

pre-existing cells!

Virchow

• Cell Theory

• that is still largely accepted today.

2. Schleiden (1838) All plants are made of cells!

Onion skin cells

German botanist

Born: April 5, 1804Died: June 23, 1881

proposed that cells were the fundamental units of plants based on observations of plant tissue [1838]

Plant cells

3. Schwann

Who came up with this theory?

All animals are made of

cells!

Human red blood cells

proposed that cells were the fundamental units of animals based on observations of

animal tissue [1839]

Born: December 7, 1810Died: January 11, 1882

/

• German zoologist

Blood

Sperm

Schleiden and Schwann

The Cell Theory [1839]• All living things are made of

cells.

• Cells exhibit the fundamental characteristics of life:– Obtain energy—photosynthesis, chemosynthesis, or digestion

– Use energy—respire

– Excrete Waste

– Show Order

– Homeostasis

– Evolve

– Reproduce

– Move

– Respond to changes in environment

– Grow and repair damage to self

The Cell Theory States:• As written by Rudolph Virchow (1821-

1902):– All living organisms are made of one

or more cells.

– Cells are the basic units of structure and function in all organisms.

– All cells come from previously existing cells.

– The activity of an entire organism depends on the total activity of its independent cells.

Definition

= Three part theory about cells

1. All living things are made of cells.

Part 2 of the Theory

2. The cell is the basic structural and functional unit of life.

Part 3 of the Theory3. All cells come from pre-existing

cells.

yeast cells dividing

How big are cells?• Microscopic

(mostly)• Measured in

microns µm • (micrometers).

• A µm is one millionth of a meter =

• 10-9 m = one thousandth of 1 mm.

How big are cells?

Smallest free-living cell = Mycoplasma genitalium

Size = 0.2 to 0.3 µm

How big are cells?• Bacteria e.g. Eschericia coli (aka

E.coli)

• Size=1 µm by 3 µm

How big are cells?• Human red blood cell =

• 8 µm in diameter

How big are cells?

• Largest cell on the human body

= ovum

• Size=

• 1000 µm in diameter

(1 mm)

How big are cells?• Smallest cell in the human body =

sperm cell.

How can we study cells?

Problem:

They are microscopic!

Solution:

Use a microscope!

Cell biology• Cell biology is the study of cell structure and

function, and it revolves around the concept that the cell is the fundamental unit of life.

• Focusing on the cell permits a detailed understanding of the tissues and organisms that cells compose.

• Some organisms have only one cell, while others are organized into cooperative groups with huge numbers of cells.

• On the whole, cell biology focuses on the structure and function of a cell, from the most general properties shared by all cells, to the unique, highly intricate functions particular to specialized cells.

Microscopes

1. Compound light microscope

– Light passes through lenses to magnify image up to 1000X

– Can observe living cells

A. COMPOUND MICROSCOPE

Light Microscope

Human Cheek Cell Nerve Cells

B. STEREOMICROSCOPE

• Gives 3D images of specimen

C. SCANNING ELECTRON MICROSCOPE (SEM)

1. Uses electrons instead of light to project surface image of specimen

SCANNING ELECTRON MICROSCOPE (SEM)

2. Electron microscope

– Uses a beam of electrons to magnify image

> 1000X– Kills cells being

observed

Scanning Electron Microscope

Human Sperm Insect Head

D. TRANSMISSION ELECTRON MICROSCOPE (TEM)

1. Works like light microscope except uses electrons

Transmission Electron Microscope

Plant Cell Mitochondrion

Comaparison of Light and Electron Microscopes

Microscopic measurementsmm – millimeters

μm – micrometer

nm - nanometers

1m = 1000mm = 1000,000μm= 1000,000,000nm

Assignment #1 which microscope can be

used to study the following Sizes of Biological Structures

• Thickness of leaf• Paramecium• Sharp end of pin• Plant cell• Animal cell• Mitochondrion• Bacterium• Ribosome• DNA molecule• Hydrogen atom

• O.5mm

• 200μm

• 100 μm

• 40μm

• 20μm

• 1μm

• 0.5-1μm

• 20nm

• 2nm

• 0.04nm

And, what about viruses?• Are not composed of cells

but consist of a nucleic acid (DNA or RNA) in a protein coat

• Yet conduct all of the cell processes (although with help, not independently)

Documents

The Development of the Cell Theory Cell Biology Prepared by: A. Abougabal