Download of cells

2.1.6 Explain the surface area to volume ration as a factor limiting cell size.
CELL SIZE
• Cell size is a critical component of how cells
function.
• Key Points about cell size:
• Metabolic reactions occur within the cell.
• The membrane controls what goes in and out of the
cell.
• THEREFORE, there has to be a correlation between cell
size (surface area of plasma membrane) and volume.
IN:
 Oxygen
 Nutrients
 Water
The plasma membrane
of a cell is the surface of
exchange for materials
between the inside and
the outside of the cell.
OUT:
 Carbon dioxide
 Waste
 Products (e.g. proteins)
http://commons.wikimedia.org/wiki/Sphere
As the cell gets larger, it requires
more resources to be imported and
produces more products (and waste)
to be exported.
Therefore, a larger volume requires
more exchange across the membrane.
Large Cell = Small SA:Vol Ratio
Small Cell = Large SA:Vol Ratio
http://commons.wikimedia.org/wiki/Sphere
As the cell gets larger, the surface area to
volume ratio actually gets smaller…
…so the exchange processes become less
efficient with increasing size.
http://commons.wikimedia.org/wiki/Sphere
Benefits of Large SA:Vol Ratio
• Diffusion Pathways are shorter (and more
efficient) in
with a larger surface
are to volume ratio.
• More surfaces for metabolic reactions
• More efficient removal of heat and waste
http://commons.wikimedia.org/wiki/Sphere
BENEFITS OF LARGE SA:VOL RATIO
• Concentration gradient are easier to generate
• Makes diffusion more efficient (takes less solute to
make 10% solution in a 100 ml beaker than a 10 L
bucket)
BENEFITS OF LARGE SA:VOL RATIO
• A Larger SA:Vol ratio means the cell can act more
efficiently. For every unit of volume that requires
nutrients or produces waste, there is more
membrane to serve it.
2.1.6 Explain the surface area to volume ration as a factor limiting cell size.
HOW TO MAXIMIZE SA:VOL RATIO
• Surface are to volume ratio is a factor that limits the size of cells.
• By dividing to make more, smaller cells, the efficiency of the exchange
processes across the membranes (into and out of the cells) can be
kept high.
• Cells Compartmentalize – organelles w/ specific functions
• Larger cells typically have in-foldings or out-foldings of plasma
membrane to increase surface area relative to their volume.
BILL
Explain the importance of surface area to
volume ratio as a factor limiting cell size.
As cells increase in size, the Surface area to volume
ratio decreases. Smaller cells have larger surface area
to volume ratios. A larger surface area to volume
ratio makes diffusion pathways shorter, increases the
area for metabolic reactions, and makes the cell more
efficient at removing waste. As a cell increases to the
point where the surface area to volume ratio is too
large that it makes the cell inefficient, it will divide
into two smaller, more efficient cells with larger
surface area to volume ratios
Free images from: Presentations ETC, University of Florida. http://etc.usf.edu/presentations/
CELLS ALIVE – INTERNET ACTIVITY
• Use the website www.cellsalive.com to answer the
questions on the worksheet
• Click on Cell Biology on the left hand side of the page
• Once you have completed the activity you may work on
your lab
Emergent Properties
the whole is
more than the sum
of its parts
Photo by Stephen Taylor: http://www.flickr.com/photos/gurustip/9668701965/in/photostream
2.1.7 State that multicellular organisms show emergent properties
EXAMPLES OF EMERGENT PROPERTIES
• Multicellular Organims
• Composed of cells, tissues, organs, and organ systems. Each has
unique properties that make up the organism, but we see the
organism as a whole entity resulting from a combination of all its
parts.
• Carbohydrate
• Composed of monomers, made of molecules joined together,
which are composed of different atoms. When put all the pieces
together, we have a carbohydrate that functions as a result of the
combo.
BILL
• Lab Reports due by 3:00 pm
• What do we mean by emergent properties? What is an
example of something that displays emergent properties?
• The whole is more than the sum of the parts.
• Multicellular organisms cellstissuesorgansorgan
systemsorganism
EMERGENT PROPERTIES (EXAMPLES)
• Ecosystem
• Each ecosystem is composed of different animals, plants, and
environmental factors (weather, rivers, lakes, etc…). Each can be
viewed separately, but when combined we see the unique ecosystem
composed of all the pieces.
CELL DIFFERENTIATION (SPECIALIZATION) OF CELLS:
• All multicellular organisms start out as a single fertilized cell
(embryo)
• Cell undergoes rapid cell division during developments and
differentiates into specialized cells (liver, heart, skin, etc…)
CELL DIFFERENTIATION
• All cells contain the same genetic material (DNA)
• Type of cell results from the expression of certain genes,
but not others in the DNA
• Genes are expressed/not expressed based on the
position/location of cell, hormones or chemicals present,
or cell-to-cell communication (other cells present)
FOOD FOR THOUGHT
• If all cells come from pre-existing cells, how do we get
all the different types of cells that exist within our
body?
STEM CELLS
Stem Cells retain the capacity to divide and can
differentiate along divergent pathways.
Totipotent
Can differentiate into any type of
cell.
Pluripotent
Can differentiate into many
types of cell.
Multipotent
Can differentiate into a few
closely-related types of cell.
Unipotent
Can regenerate but can only
differentiate into their associated
cell type
(e.g. liver stem cells can only make
liver cells).
Image from: http://en.wikipedia.org/wiki/Stem_cell
Stem Cells retain the capacity to divide and can
differentiate along divergent pathways.
By Fwfu at en.wikibooks [Public domain], from Wikimedia Commons
http://commons.wikimedia.org/wiki/File%3AStemcelldifferentiaion.jpg
Therapeutic Uses of Stem Cells
Treatment for Leukemia
From:
Problem
Cancer of the blood or bone marrow,
resulting in abnormally high levels of poorlyfunctioning white blood cells.
Treatment
Chemotherapy and radiotherapy can be used
to destroy the white blood cells, but these
need to be replaced with healthy cells. Bone
marrow transplants are often used for this.
Role of
Stem Cells
Hematopoetic Stem Cells (HSCs) can be
harvested from bone marrow, peripheral
blood or umbilical cord blood. As these can
differentiate to form any type of white blood
cell, they can be used to repopulate the bone
marrow and produce new, healthy blood cells.
The use of a patient’s own HSCs means there
is far less risk of immune rejection than with a
traditional bone marrow transplant.
http://en.wikipedia.org/wiki/Pluripotential_hemopoietic_stem_cell
Animation of this process:
Animated tutorials from: http://outreach.mcb.harvard.edu/animations/thera7c.swf
Two Minute Essay
What is a stem cell?
How do stem cells differentiate into specialized cells?
Outline one therapeutic use of stem cells.
Free images from: Presentations ETC, University of Florida. http://etc.usf.edu/presentations/