Download - Cell Biology
Cell Biology
Honors CS2
Ms. Levensailor
The Cell Theory
All living things are made of cells!– Lowest level of structure.
Cells are the basic unit of structure and function in living things!– Capable of performing all the activities of life.
All cells come from pre-existing cells.
Two Major Classes of Cells
Prokaryotic Cells: lacks a nucleus and other organelles.– Bacteria– Archaea
Eukaryotic Cells: has a nucleus and organelles surrounded by membranes.– Protists, fungi, plants and animals
Eukaryotic
Greek meaning “true kernel”– Kernel refers to the nucleus
10 to 100 micrometers
Prokaryotic
Much simpler in structure Smaller in size (1 to 10 micrometers in
diameter)
Cell Size
Size directly relates to function! Logistics of carrying out metabolism sets
limits to cell size. Lower limits: Mycoplasmas (bacteria)
– Smallest packages with enough DNA to program metabolism
– Also enough enzymes to sustain itself and reproduce.
Cell Size Continued
Upper limits: as a object increases in size, its volume grows proportionately more than its surface area. – Area is proportional to a linear dimension squared
cm2
– Volume is proportional to the linear dimension cubed.
cm3
Surface-to-Volume Ratio
The smaller the object, the greater its ratio of surface area to volume.
Area / Volume
Cell shape and rates of diffusion
With your face partner do pre-lab 6 www.biology.com A high surface-to-volume ratio facilitates the
exchange of materials between a cell and its environment.
Cell shape and rates of diffusion
Plasma membranes function as a selective barrier that allows sufficient passage of:– Oxygen, nutrients, and wastes
For each square micrometer of membrane, only so much of a particular substance can cross per second.
Cell shape and rates of diffusion
If a cell were very large, rates of chemical exchange would be inadequate to maintain the cell.
This explains the microscopic size of most cells.
Larger organisms don’t have larger cells, just more cells.