CELL DISCOVERY AND THEORY7.1

History of the Cell Theory

1665: Robert Hooke discovered cellulae using a microscope and cork

Cell: basic structural and functional unit of all living things

The Cell Theory

fundamental idea of modern biology

Consists of 3 principles: All living organisms composed of 1+

cells Cells are basic unit of

structure/organization of all living organisms

Cells arise only from previously existing cells, with cells passing copies of their genetic material on to their daughter cells

As magnification and resolution increases, so do the details we can

see!

Microscope Technology

Compound Light Microscopes

Made of several glass lenses and uses visible light to magnify images Each lens magnifies image of previous lens (ex. 10 x 10 = 100x)

Dyes used to see the cells better

Limitations: objects cause light to scatter, blurring images Max magnification without blurring is

~1000x

Electron Microscopes

Developed during 1940s

Uses magnets to aim a beam of electrons at thin slices of cells

SEM, TEM, STM

Transmission Electron Microscope (TEM)

electrons passed through a specimen to a fluorescent screen

thick parts of specimen absorb more electrons, creating shaded image

*Shows internal details (more like an xray)

can magnify up to 500,000x but specimen must be dead, sliced very thin, and stained with heavy metals

Scanning Electron Microscope (SEM)

Sends electrons over specimen’s surface,creating a 3D image

Disadvantages: TEM and SEM only used for non-living cells/tissues

Scanning Tunneling Electron Microscope (STM)

Charged tip of probe brought to specimen so that electron “tunnel” through small gap between them

Allows scientists to create 3D models of

objects as small as atoms

Advantage: Can be used with live specimens

Atomic Force Microscope (AFM)

Measures forces between tip of probe and cell surface

Image is a scan of a crystal of satellite tobacco mosaic virus particles

Basic Cell Types

Cells have different shapes/sizes and differ based on function

All cells have a plasma membrane! special boundary that helps control what

enters/exits the cell

All cells have some functions in common Most have genetic material that provides

instructions for making substances that the cell needs

2 main groups: eukaryotic and prokaryotic Eukaryotic cells are ~100x larger than prokaryotic

Organelles: specialized structures that carry out specific functions Bound by membranes Allow functions to occur in different places at

the same time

Nucleus: a central organelle that contains cells genetic material (DNA)

Eukaryotic cells believed to have evolved from prokaryotic cells

PROKARYOTIC CELLS EUKARYOTIC CELLSPlasma membrane Plasma membrane

No organelles Has organellesOrganisms prokaryotes Organisms eukaryotesMake up most unicellular

organisms (bacteria)Make up most organisms and some unicellular organisms

(algae and yeast)

Cell Size

Cells are TINY! Some are as small as 1/1000th of a millimeter.

Small cells have more surface area per volume More surface area makes it easier to move material

in/out of the cell

Large cells have less surface area per volume Requires more nutrients, produces more wastes

CONCLUSION: Cells need a certain surface area to properly function (exchange materials). Surface area to volume considerations are the reason why cells stay small!