 If you have not already done so, turn in your microscopy lab.  Place the following molecules/organisms in order of increasing size. ◦ Virus ◦ Bacteria ◦ Cell Membrane, ◦ Plant Cell ◦ Animal Cell  Cell Membrane  Virus  Bacteria  Animal Cell  Plant Cell

 Cell size is a critical component of how cells function.  Key Points about cell size: ◦ Most chemical reactions occur within the cell and its size affects the rate of these reactions. ◦ 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. ◦ Surface area to volume ratio is a factor that limits the size of cells Explain the surface area to volume ration as a factor limiting cell size.

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. Larger cells have small surface area to volume ratio and less efficient exchange processes Large Cells

 Larger cells have comparatively (relative) less surface area than smaller cells.  To compensate, larger cells typically have infoldings or outfoldings of plasma membrane to increase surface area relative to their volume Explain the surface area to volume ration as a factor limiting cell size.

 Smaller Cells require less resources to be imported and produces less to be exported.  Therefore, a smaller volume requires less exchange across the membrane.  Smaller cells have large surface area to volume ratio and more efficient exchange processes

 Large cell = Small SA:V ratio (inefficient)  Small cell = Large SA:V ratio (efficient)  When cells become too large, they will divide into two smaller cells with large surface area to volume ratios

 Surface area 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.

 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.

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)

2.1.6 Explain the surface area to volume ration as a factor limiting cell size.

Free images from: Presentations ETC, University of Florida. 2-minute convo 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

Emergent Properties Photo by Stephen Taylor: the whole is more than the sum of its parts

2.1.7 State that multicellular organisms show 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.

 Come up with some examples of things that could show emergent properties.

 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.

 Explain how surface area to volume ratio limits 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

 All multicellular organisms start out as a single fertilized cell (embryo)  Cell undergoes rapid cell division during developments and differentiates, or become specialized, into specific cells, tissues, and organs that carry out specific functions (nerve cell, muscle fibers, liver, heart, skin, etc…)

 All cells contain the same genetic material (DNA)  Type of cell results from the expression of certain genes, and 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)

 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 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others

 Stems cells retain the capacity to divide and DIFFERENTIATE into various cells (liver, heart, skin, etc.) Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others

 Embryonic Stem Cells – found in the inner cell mast of the blastocyst (formed soon after fertilization)  Adult Stem Cells – can be found in babies, children, and adults, and are undifferentiated cells found in various tissues throughout the body (umbilical cord, bone marrow, mammary cells, intestinal cells)  /thera7c.swf /thera7c.swf

Stem Cells retain the capacity to divide and can differentiate along divergent pathways. Totipotent Can differentiate into any type of cell. (Embryonic) Pluripotent Can differentiate into many types of cell. (Embryonic) Multipotent Can differentiate into a few closely-related types of cell. (adult) Unipotent Can regenerate but can only differentiate into their associated cell type (e.g. liver stem cells can only make liver cells). Image from:

 Stargardt’s Disease ◦ Inherited disease that causes cells in the retina (back of the eye) to deteriorate, resulting in vision loss  Treatment for Stargardt’s disease ◦ Stem cells designed to protect and regenerate parts of the eye (photoreceptors) that are damaged by the disease. ◦ 7c.swf 7c.swf

Therapeutic Uses of Stem Cells Animated tutorials from: Animation of this process:

Outline therapeutic use of stem cells