1. Introduction to Cells

2. 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

3. 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

4. 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

5. The Discovery of Cells The first person to observe living cells was a Dutch trader named Anton van Leeuwenhoek In 1673 Leeuwenhoek observed protists

6. 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

7. 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

8. 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

9. The Cell Theory These discoveries led Rudolf Virchow to observe that all cells come from existing cells These discoveries helped shape “The Cell Theory”

10. 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

11. 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

12. 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

13. Video http://www.youtube.co m/watch?v=SfNs_PmEX II http://www.youtube.co m/watch?v=SfNs_PmEX II

14. 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

15. 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?

16. 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

17. 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