The Microscope & The Cell

The Modern Miscroscope


































A little bit of History:

Microscopes were invented less than 400 years ago.  A hand lens is a simple microscope that allows us to view small items. 

  • Anton von Leeuwenhoek used a simple microscope (a microscope with only one lens) to become the first person to view and describe the miniature world of protozoa and bacteria.  He drew detailed images of what he saw.









                                       von Leeuwenhoek's microscope                                                                                                           What von Leeuwenhoek saw


  • Robert Hooke devised the compound microscope (a microscope with multiple lenses) and an illumination system, and coined the term "cells":  the boxlike cells of  cork tree bark reminded him of the cells of a monastery












                             Hooke's Microscope                                         What Hooke saw, and his first drawings of cells


These, and other microscope makers, allowed us the first glimpse into the smallest units of life.


What they saw

Sceintists saw tiny animals (called now called protists), and plant cells.  They weren't able to see a lot of what was inside the cells yet.  that came when the technology improved.

However, scientists did learn that everything that was alive seemed to be made of cells.  They also noticed that larger organisms were made up of cells that were all about the same size, just more of them.  These two ideas became an iportant part of Cell Theory.


We had to wait for Luis Pasteur  before we got the last bit of Modern Cell Theory.  Pasteur was able to debunk (disprove) the idea of spontaneous generation - quite a feat, considering everyone pretty much believed it, even my  grandmother belived it when I was a child;  that living things could just "pop up" out of nothing.  My grandmother was convinced that garbage left in the house would turn into mice and rats.  When you think about it, it isn't that farfetched an idea - garbage piles usually have rats and mice around them.  But the process that brought he two together was what grandma didn't quite get.  Pasteur developed an elegant experiment that disproved spontaneous generation, and Modern Cell Theory was established.


So what is this Modern Cell Theory?

Simply put, the modern cell theory has three parts:

  1. Cells are the basic unit of Function and Structure of all living things.  Cells are the smallest units of life that can function independently and perform all the necessary functions of life.


  1. All living things are composed of one or more cells

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

  3. Cells come only from existing cells (the reproduction of other cells)


What kinds of cells are there?

All living things are made of cells.  Some types of cells are much more complex than others.

We  divide cells into TWO types, based on internal complexity:

1. Prokaryote cells

Typical PROKARYOTIC features

      •  No nucleus—DNA floats unprotected in the cytoplasm 

      • Internal structures not organized into compartments

      • Always Unicellular (single celled organisms)

      •  Have a cell wall like a plant cell

      • Some capture sunlight energy (like plants) via photosynthesis, but do not have Chloroplasts

2. Eukaryote cells

Typical EUKARYOTIC features 

      •  Has nucleus— DNA is protected inside the nucleus

      • Internal structures are organized into compartments

      • May be Unicellular (single celled organisms) or Multicellular

      •  Larger than Prokaryotes – usually 10 times larger

      • Cytoplasm contains specialized structures called Organelles














But there are other ways to differentiate between cells:

Cells can also be divided by how they obtain their energy. 

  • Autotrophs:  Some organisms (both Prokaryote and Eukaryote) can get their energy directy from  sunlight energy.  These organisms are plants, protists and algae (algaes are like plants in that they are green and capture sunlight energy; they are different because they are single cells.  Plants are always multicellular). 
    The word Autotrophs is a compound word, made up of two parts:  Auto = Self;  Troph = Feeding

  • Heterotrophs: Other organisms (again, both Prokaryote and Eukaryote) cannot get their energy diretly from sunlight energy. These organisms are animals and some protists (Protists are like animals in that they cannot capture sunlight energy and have to eat to get their energy; they are different because they are single cells.  animals are always multicellular). 
    The word Heterotroph is likewise a compound word made up of two parts:  Hetero = Other;  Troph = Feeding


I have mentioned Protists a bit in the above descriptions, but we will not be talking about them in our class.  Protists are an unusual grouping of organisms, and aren't very well understood.  WHile they have fascinating attributes, they become a distraction in our discussions, as they tend to break the  rules.  So we won't be mentioning them again.

















 Autotroph - notice the difference in the cell parts                                                              Heterotroph - these can't capture their energy, but have to eat.


This is, of course, a very simplified introduction to the cell.  Scientists saw parts inside the cell (just like you see them now), and had no idea what function each part had.  It took years of examining cells, experimenting, and analyzing information before the mechanisms of each of these parts were determined, and more discoveries are sure to follow.


Scientists also realized that not all cells are alike, especially in a multicellular organism (an organism made up of more than one cell).  In multicellular organisms, cells take on specialized roles.  Your brain cells do different things than your stomach cells.  Each has its own function, shape, chemistry, and purpose.  these cells are not interchangable cogs in a machine, but are specialized parts that perform specific functions.


Our bodies contain many hundreds of distinct cell types.  I have listed two above (brian and stomach), and I am sure you could come up with many more.  Wikipedia lists more than seven pages of different cell types in human beings.  Each of these cell types has its own function and purpose.  We'll see more about how the purpose and shape are interrelated.


Each single cell in our bodies is an intricate system, a factory in miniature, that operates unceasingly every second of its life.