The Importance of
Surface Area
Size as a limiting factor
• Within each cell
there are a variety
of molecules and
organelles
Size as a limiting factor
• Cells are limited in size due
to the surface area/volume
ratio
• The larger the cell  the more
energy it needs  the higher
the rate of metabolism
• Higher metabolism  increased
fuel needs
• However, due to increased size,
the rate of diffusion is slower
Size as a limiting factor
• As cells increase in size,
they become less
efficient because the
surface area/volume
ratio decreases
• There are not enough
doorways to transport the
needed amount of molecules
into the cell
• The molecules that enter the
cell have too far to travel
• Your cells can’t wait 2 hours
for ATP, they need it now!
Cell division
• Cells divide when they become too large to effectively
carry out metabolic functions
• Smaller cells have the following advantages:
•
•
•
•
Faster rate of diffusion & osmosis
Adequate resources such as RNA
Greater differentiation of jobs
Faster travel (think sperm)
SA/V ratio not just limited to cell size
small intestine
mitochondria
brain
Oooooh!
Form fits
function!
Implications of the SA/V Factor
• Keeping cells
smaller, keeps
the rate of
diffusion fast
Implications of the SA/V Factor
• Limiting size helps cell carry out life functions efficiently
• Cells can specialize
• Characteristics are designed for specific functions
• i.e. muscle cells with multiple mitochondria to carry out cellular
respiration
• Multicellular organisms can show emergent properties
• Cells of the organism interact as a whole rather than individually
• Multicellular organisms often have cells organized into
tissues, organs, and organ systems.
Any Questions??