Download File

SIZE AND SHAPE
BY STEPHEN JAY GOULD
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Like eukaryotic cells, before larger animals could
evolve, they needed to increase vital surface areas.
Can you name these features?
• Nutrient Absorption?
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Nutrient Absorption? The villi of the small intestine.
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Gas Exchange in the lungs?
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Gas Exchange in the lungs?
• Alveoli: the grape-like clusters with a rich blood
supply.
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Gas Exchange in tissues?
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Gas Exchange in tissues?
• Capillaries are one RBC in diameter.
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• The strength of a leg bone?
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• The strength of a leg bone?
• …depends upon the area of its cross section.
• If bones grew proportionately (s.a.)2 they would not support the mass
(vol.)3 of the organism. The bones would break.
CLICK THE LINK TO GO TO BOZEMAN BIOLOGY FOR
A DISCUSSION OF SURFACE AREA AND VOLUME.
• Mr Anderson talks about why cells are small. (5:54 min)
• https://www.youtube.com/watch?v=wuXSEOKNxN8
AS A CELL GROWS, HOW DO SURFACE
AREA AND VOLUME INCREASE?
AS A CELL GROWS, HOW DO SURFACE
AREA AND VOLUME INCREASE?
Surface area increases by the square of length
while volume increases by the cube of length.
AS VOLUME INCREASES, HOW DOES RELATIVE
SURFACE AREA CHANGE COMPARED TO VOLUME?
AS VOLUME INCREASES, HOW DOES RELATIVE
SURFACE AREA CHANGE COMPARED TO VOLUME?
Surface area decreases relative to volume.
There is an upper limit on cell size.
What is the limiting factor?
There is an upper limit on cell size.
What is the limiting factor?
Surface Area
WHY IS THIS IMPORTANT TO CELLS?
WHY IS THIS IMPORTANT TO CELLS?
• Many functions that depend upon surfaces
must serve the entire volume of the cell.
WHY IS THIS IMPORTANT TO CELLS?
• Many functions that depend upon surfaces
must serve the entire volume of the cell.
• Three examples:
• Food supply in, wastes out.
• Gasses must be exchanged across surfaces. Oxygen
must diffuse in, Carbon Dioxide diffuses out.
• From the paper: strength of a leg bone depends
upon the area of its cross section.
SUBSTITUTE “SUPPLY OF FOOD” FOR SURFACE AREA
AND “METABOLIC DEMAND” FOR VOLUME.
• Surface area increases by the square of length while
volume increases by the cube of length.
SUBSTITUTE “SUPPLY OF FOOD” FOR SURFACE AREA
AND “METABOLIC DEMAND” FOR VOLUME.
• Surface area increases by the square of length while
volume increases by the cube of length.
• As a cell grows, the supply of nutrients increases by
the square of length while the metabolic demand
increases by the cube of length.
• When the supply of nutrients can no longer meet
the metabolic demand, the cell must stop growing.
• Continued growth would result in the cell….
SUBSTITUTE “SUPPLY OF FOOD” FOR SURFACE AREA
AND “METABOLIC DEMAND” FOR VOLUME.
• Surface area increases by the square of length while
volume increases by the cube of length.
• As a cell grows, the supply of nutrients increases by
the square of length while the metabolic demand
increases by the cube of length.
• When the supply of nutrients can no longer meet
the metabolic demand, the cell must stop growing.
• Continued growth would result in the cell starving or
poisoning itself.
There is an upper limit on cell size.
What is the limiting factor?
There is an upper limit on cell size.
What is the limiting factor?
Surface Area
NOW, EQUATE SUPPLY OF NUTRIENTS TO
METABOLIC DEMAND WHEN THE CELL DIVIDES.
?
NOW, EQUATE SUPPLY OF NUTRIENTS TO
METABOLIC DEMAND WHEN THE CELL DIVIDES.
• As a cell divides, the supply of nutrients decreases
by the square of length while the metabolic
demand decreases by the cube of length.
NOW, EQUATE SUPPLY OF NUTRIENTS TO
METABOLIC DEMAND WHEN THE CELL DIVIDES.
• As a cell divides, the supply of nutrients decreases
by the square of length while the metabolic
demand decreases by the cube of length.
• This results in a favorable surface area to volume
ratio.
NOW, EQUATE SUPPLY OF NUTRIENTS TO
METABOLIC DEMAND WHEN THE CELL DIVIDES.
• As a cell divides, the supply of nutrients decreases
by the square of length while the metabolic
demand decreases by the cube of length.
• This results in a favorable surface area to volume
ratio.
• To make an organism larger, the cell doesn’t get
bigger, it divides to create many cells.
PROKARYOTIC CELLS HAVE INCREASED THEIR
SURFACE AREA USING INFOLDING OF THE PLASMA
MEMBRANE.
Aqua: Mesosome
Red: Inclusion body
Blue: Nucleoid
Purple: Membrane
Brown: Cell wall
The folds of membrane in this
cyanobacterium house the
enzymes for photosynthesis.
More surface area for
enzymes, more sugar.
HOW CAN EUKARYOTIC CELLS BE SO MUCH BIGGER
THAN PROKARYOTIC CELLS?
HOW CAN EUKARYOTIC CELLS BE SO MUCH BIGGER
THAN PROKARYOTIC CELLS?
Eukaryotic cells evolved when prokaryotic cells added
surface area in the form of membrane-bound
organelles. This allowed their volume to become
greater than prokaryotic cells. Eukaryotic cells are
about 10x bigger than prokaryotic cells.
HOW CAN EUKARYOTIC CELLS BE SO MUCH BIGGER
THAN PROKARYOTIC CELLS?
Organelles allowed for the formation of compartments within the cell which was important in the
progressive evolution of larger and more complex
organisms.
IF AN ORGANISM IS ONE CELL BIG, HOW IS OXYGEN
BROUGHT IN AND CARBON DIOXIDE EXPELLED?
IF AN ORGANISM IS ONE CELL BIG, HOW IS OXYGEN
BROUGHT IN AND CARBON DIOXIDE EXPELLED?
• Diffusion
IF AN ORGANISM IS ONE CELL BIG, HOW IS OXYGEN
BROUGHT IN AND CARBON DIOXIDE EXPELLED?
• Diffusion
• Which cell organelle is responsible for controlling
what enters and leaves the cell?
IF AN ORGANISM IS ONE CELL BIG, HOW IS OXYGEN
BROUGHT IN AND CARBON DIOXIDE EXPELLED?
• Diffusion
• Which cell organelle is responsible for controlling
what enters and leaves the cell?
• The plasma membrane.
IF AN ORGANISM IS ONE CELL BIG, HOW IS OXYGEN
BROUGHT IN AND CARBON DIOXIDE EXPELLED?
• Diffusion
• Which cell organelle is responsible for controlling
what enters and leaves the cell?
• The plasma membrane.
• Is the plasma membrane a surface or a volume?
• Surface
• Therefore, as the cell grows, the plasma membrane
or rate of diffusion increases by the square of
length.
WHAT IS THE LIMITING FACTOR FOR CELL SIZE?
SURFACE AREA OR VOLUME?
WHAT IS THE LIMITING FACTOR FOR CELL SIZE?
SURFACE AREA OR VOLUME?
COMPARTMENTALIZATION
• The benefits include:
COMPARTMENTALIZATION
• The benefits include:
• Simultaneous reactions can occur. (ex. Photosynthesis & cellular respiration
COMPARTMENTALIZATION
• The benefits include:
• Simultaneous reactions can occur. (ex. Photosynthesis & cellular respiration
• Concentration of reactants increasing metabolic
efficiency. (ex. E.R. and Golgi)
COMPARTMENTALIZATION
• The benefits include:
• Simultaneous reactions can occur. (ex. Photosynthesis & cellular respiration
• Concentration of reactants increasing metabolic
efficiency. (ex. E.R. and Golgi)
• Maintaining a pH different than the cytoplasm for
the optimal reaction rate of enzymes needed in
specific reactions. (ex. mitochondria, chloroplasts)
COMPARTMENTALIZATION
• The benefits include:
• Simultaneous reactions can occur. (ex. Photosynthesis & cellular respiration
• Concentration of reactants increasing metabolic
efficiency. (ex. E.R. and Golgi)
• Maintaining a pH different than the cytoplasm for
the optimal reaction rate of enzymes needed in
specific reactions. (ex. mitochondria, chloroplasts)
• Storage of digestive enzymes safely away from the
rest of the cell. (ex. Lysosomes)
COMPARTMENTALIZATION
• The benefits include:
• Simultaneous reactions can occur. (ex. Photosynthesis & cellular respiration
• Concentration of reactants increasing metabolic
efficiency. (ex. E.R. and Golgi)
• Maintaining a pH different than the cytoplasm for
the optimal reaction rate of enzymes needed in
specific reactions. (ex. mitochondria, chloroplasts)
• Storage of digestive enzymes safely away from the
rest of the cell. (ex. Lysosomes)
• Separation & control of processes. (ex: transcription
and translation)
THIS SHOWS A WHITE (PURPLE) AND RED BLOOD
CELL NEXT TO A BACTERIAL CELL (GREEN). NOTE
THE SIZE DIFFERENCE.
WHY ARE INTERNAL ORGANS IMPORTANT IN THE
PROGRESSIVE EVOLUTION OF LARGE ORGANISMS?
• Hint
• Cell : Organelles ::
• Organism : Organs