Cell theory and size

2.1.1 Outline the cell theory


  • Cells are the smallest unit of life
  • All organisms are composed of one or more cells
  • All cells come from pre-existing cells

2.1.2 Discuss evidence for the cell theory

Earliest evidence:
Robert Hooke first described cells in 1665 while observing cork with a microscope he built himself.
The 'pores' reminded him of the small cubicles occupied by monks in a monastery, so he took the Latin word "cella" meaning a little room and gave it to what he saw. Hence the word "cell" today.

The diagram below is Hooke's drawing of what he saw.

external image hooke.jpg

Robert Hooke with his microscope:
external image C5_CellTheory_1.GIF

2.1.3 State that unicellular organisms carry out all of the functions of life

  • metabolism
  • growth
  • reproduction
  • response
  • homeostasis
  • nutrition

2.1.4 Compare Cell size

external image cellsize_1.gif

2.1.5 Calculate magnification

scale bar
scale bar

To determine MAGNIFICATION (M) divide the scale bar length by the number given
The units must be converted to the same value (note that microns = micrometers)
  • M = 1 cm divided by 10 microns = 10,000 microns divided by 10 microns
M = 1000
To determine the REAL SIZE, measure the object and divide by Magnification (in this case by 1000)

2.1.6 Explain surface area/volume relationship This graph shows how quickly volume (cubic) increases in comparison to surface area (area). For adequate cell diffusion, the cell SA must be be kept high in relationship to the volume. this limits the size that the cell can grow. external image area.gph2.gif

Examples of how increased surface ara to volume increases diffusion of a) heat and b) iron particles

external image sareatovolume2.jpg

external image slide20.gif

2.1.7 State that multicellular organisms show emergent properties 2.1.8 Explain multicellular organism cells differentiate to perform different functions by expressing some of their genes but not others. external image a2%20cell%20differentiation.gif external image rlb1a.jpg 2.1.9 State that stem cells retain the capacity to divide and differentiate along different pathways external image stem-cell-diagram-nih.jpg The following link shows stem cell life http://www.dnalc.org/stemcells.html Stem cells can be produced by cloning:

Stem cell breakthrough
Stem cell breakthrough

Stem cell breakthrough

2.1.10 Outline one therapeutic use of stem cells

Stem cells can be used to replace injured or degenerating tissue. Stem cells from embryos or from cloning can be used.
Parkinson's and Alzheimer's disease are caused by a loss of brain cells and implanted stem cells could replace these cells, thus, lowering the symptoms of these diseases.

external image 15stemcells_em.gif