Welcome to Cell Biology!

• it's alive!

Cell Theory

• 2.1: Outline the Cell Theory• 2.1.2: Discuss the Evidence for Cell Theory

Cell Theory

1. Living organisms are composed of cells2. Cells are the smallest unit of life3. Cells come from pre-existing cells, by division

(so that new cells cannot be constructed from non living substance)

The History of Cell Theory

Let’s meet who discovered cells…Meet the Scientists...

1. All living things are made of cells…

Digestive Tissue Goblet Cells http://www.olympusmicro.com/galleries/abramowitz/index.html 6.11.12

How do we know that all living things are made of cells?

Because we can SEE them through microscopes….

When we we first start talking about ‘Cells’?

Robert Hooke coined the term ‘cells’ since he felt that the space-filled chambers of dead cork resembled a monk’s empty cell…

Cell Theory: Robert HookeMicrographia, 1665:

. . . I could exceedingly plainly perceive it to be all perforated

and porous, much like a Honey-comb, but that the pores of it

were not regular. . . . these pores, or cells, . . . were indeed the first microscopical pores I ever saw,

and perhaps, that were ever seen, for I had not met with any Writer

or Person, that had made any mention of them before this. . .

The Father of Microscopy: Van Leeuwenhoek

The first man to visualise single-celled animals (he called protists animacules): 1674Microscopy bytes

Nothing smaller can survive independently

If a cell is broken down into its individual components, its

subunits cannot survive independently

3.All cells come from pre-existing cells: ‘Omnis Cellula e cellula ‘

• Disproving spontaneous generation

• Pasteur

Limitations to cell theory

Limitations 1: There are many unicellular organisms

• Mobile amoeba

Primitive unicellular organisms carry out all of the functions of life• Prostista • Paramecium• Amoebae• Giant amoebae!

Limitations to cell theory: multinucleated cells (syncytiae)

• Skeletal and cardiac muscle

Limitations to cell theory: multinucleated cells (syncytiae)

Fungal hyphae (phase contrast microscopy)

How large are cells?

Let's put things into perspective....

What units do we use to measure cells and cell components?

Size is relative….

Organism Size

Prokaryotic cell 1 – 10 μm

Animal Cell 10 – 30 μm

Plant Cell 10 – 100 μm

Virus < 100 ηm

DNA molecule 2 ηm

Phospholipid membrane 10 ηm

How do microscopes work?

• Anatomy of vision

Magnification and scale bars

• You will often need to calculate the actual size of a specimen/ component of a cell from a microscope image, or a photograph/micrograph

• The first step is to ensure that all parts of your calculation have the same units!!

Magnification = size of imageactual size of

specimen