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

IN:  Oxygen  Nutrients  Water OUT:  Carbon dioxide  Waste  Products (e.g. proteins) The plasma membrane of a cell is the surface of exchange for materials between the inside and the outside of the cell.

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

As the cell gets larger, the surface area to volume ratio actually gets smaller… …so the exchange processes become less efficient with increasing size.

Benefits of Large SA:Vol Ratio

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. 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.

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.

Free images from: Presentations ETC, University of Florida. 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

CELLS ALIVE – INTERNET ACTIVITY Use the website to answer the questions on the worksheetwww.cellsalive.com 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 Photo by Stephen Taylor: the whole is more than the sum of its parts

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:

By Fwfu at en.wikibooks [Public domain], from Wikimedia Commons Stem Cells retain the capacity to divide and can differentiate along divergent pathways.

Therapeutic Uses of Stem Cells Animated tutorials from: Treatment for Leukemia Problem Cancer of the blood or bone marrow, resulting in abnormally high levels of poorly- functioning 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. From : Animation of this process:

Free images from: Presentations ETC, University of Florida. Two Minute Essay What is a stem cell? How do stem cells differentiate into specialized cells? Outline one therapeutic use of stem cells.