Cells IntroDefining Life
Cell Theory
Cell Size
Prokaryotic vs. Eukaryotic
Animal vs. Plant
Organelles
Magnification
Defining Life
Does it grow? Does it reproduce? Does it use energy? Does it respond to environmental stimuli? Does it have order? Does it regulate its internal environment? Does it show evidence of evolutionary adaptation?
Cell Theory
All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of
many cells Unicellular organisms (example: bacteria) are composed of
only one cell.
Cells are the smallest unit of life. They are the smallest structures capable of surviving on their own. See previous slide
Cells come from pre-exsisting cells and cannot be created from non-living material. Gooseneck flask experiment
Evidence for Cell Theory
No such thing as spontaneous generation
Pasteur’s experiment
Cell Size
Surface area of cell responsible for exchange of nutrients and waste products
Volume of cell responsible for cellular functions (e.g. cell respiration)
Volume
Volume determines the amount metabolism in the cytoplasm
Metabolism will require import of precursors
Metabolism will result in the export of secretions
And the export of excretory products
© 2007 Paul Billiet ODWS
Surface area Surface area will determine the exchange of
materials between the cell and its environment
Bigger cells will metabolise more But they will need more surface to support that
metabolism And the sites of metabolism in bigger cells will
be further from the surface of the cell
© 2007 Paul Billiet ODWS
Growing cells
1µm
2µm
3µm
4µm
5µm
6µm© 2007 Paul Billiet ODWS
How are surface area and volume affected by growth?
11.21.5236
216125642781
2161509654246
654321
SA/V
Volume / µm3
Surface area / µm2
Size / µm
© 2007 Paul Billiet ODWS
Comparing Surface Area and Volume changes
0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4 5 6 7 8 9 10
Size / µm
Surface areaVolume
© 2007 Paul Billiet ODWS
Surface Area:Volume Ratio
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9 10
Size / µm
SA
/V
© 2007 Paul Billiet ODWS
Solving the problem
Bigger cells have a greater metabolism than smaller cells
BUT bigger cells have a proportionally less surface for exchange
How to increase surface area with increasing size?
© 2007 Paul Billiet ODWS
Throw out extensions
Microvilli of small intestine epithelium
© copyright 2001 Gwen V. Childs, Ph.D., University of Arkansas for Medical Sciences
Flatten into a thin film
Chick blastodisc© Developmental Biology Online © Developmental Biology Online
Divide the cytoplasm into smaller volumes
Early human embryos
Zygote
8-cell Embryo
© Reproductive Medicine and Fertility Center
Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
© Illinois Enviromental Protection Agency© Text 2007 Paul Billiet ODWS
Multicellular organisms show the same adaptations
Mammals have a long small intestine with internal folding to absorb digested food
lithograph plate 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918. This image is in the public domain because its copyright has expired
© Text 2007 Paul Billiet ODWS
Prokaryotic vs. Eukaryotic
Prokaryotic cells No nucleus Circular DNA No histone proteins No membrane bound organells Simple ribosomes
Eukaryotic cells Nucleus Linear DNA (chromosomes) Histone proteins Membrane bound organelles Complex ribosomes
Animal vs. Plant
In animals but not plants: In plants but not animals:
Lysosomes Cell Wall
Centrioles Centrosomes
Flagella Chloroplasts
Central Vacuole
Organelles
http://library.thinkquest.org/12413/structures.html
Magnification
Magnification = Size of image (Units must be the same)Actual size
If a red blood cell has a diameter of 8 μm and a student shows it with a diameter of 40 mm in a drawing, what is the magnification of the drawing?
A.× 0.0002B.× 0.2C.× 5D.× 5000