Introduction to Cells

The Discovery of Cells

• Before cells, people believed in “humours”

• This was the idea that living things were made of elements

• Those were phlegm, blood, bile or black bile

• People had no way to see on a cellular level

The Discovery of Cells

• In 1665, English scientist Robert Hooke looked at various items of nature

• He looked through his light microscope on the bark of a cork oak tree

• What he saw changed science

The Discovery of Cells

• He saw a grouping of boxes that reminded him of cubical or cells where monks live

• The little boxes were dead plant cells

• He then went on to observe other specimens and determined that many things were made of cells

The Discovery of Cells

• The first person to observe living cells was a Dutch trader named Anton van Leeuwenhoek

• In 1673 Leeuwenhoek observed protists

The Discovery of Cells

• Protists are very small microorganisms

• This was the first time that living organisms were seen

• It was also the first time that people started to realize that the world around them was made up of living organisms

The Cell Theory

• Even though there were Cells were recorded and observed by Hooke and Leeuwenhoek, scientists did not start to put the pieces together until much later

• Around 150 years later scientists started to believe that all things were made of cells

The Cell Theory

• In 1838 German botanist Matthias Scheiden concluded that all plants were made of cells

• In 1839 German zoologist Theodor Schwann concluded the same thing for animals

The Cell Theory

• These discoveries led Rudolf Virchow to observe that all cells come from existing cells

• These discoveries helped shape “The Cell Theory”

The Cell Theory

• The Cell Theory– All living thing are

composed of one or more cells

– Cells are the basic units of structure and function in an organism

– Cells come from existing cells

Current Microscopes

• Since the advent of computers there have been great advances in microscope technology

• Scanning electron microscopes (SEMs) produce high resolution images of the surface of cells

• Transmission electron microscopes (TEMs) produce high resolution images of the insides of cells

Current Microscopes

• While these microscopes do produce high quality images of things that are not viewable by light microscopes, they do have drawbacks

• For both SEMs and TEMs samples must be prepared in ways that will kill cells that are viewed

Video

• http://www.youtube.com/watch?v=SfNs_PmEXII

Cell Size

• There are many different types of cell shapes

• Some cells are long and skinny

• Some cells are smooth and pliable

• Some cells are rigid and supportive

Cell Size

• Many cells differ in size– Cells can be one

nanometer– Cells can be as large as

the period on a piece of paper

• Why do you think that all cells are small?

Cell Size

• The size of the cell is limited by the surface area to volume ratio

• The surface area to volume to ratio is

Surface Area

Volume

Cell Size

• This means that as a cell is limited by the size of the surface area

• As the surface area goes up, the volume goes up

• This decreases the surface area to volume ratio