Sir Ken Robinson Changing Education Paradigm L4U L4U

2.1.6 Explain SA/V ratio as a factor of limiting cell size Cell size is limited by its need to exchange materials with its environment If a cell is too large, its diffusion distance becomes too long to be efficient because its SA/V ratio becomes too small to allow the necessary exchange Rate at which a cell produces heat/waste and consumes resources (food and oxygen) is directly proportional to its volume Since uptake of resources and removal of waste goes via the cell membrane, the rate of uptake/removal is proportional to its SA

Fill in the following table: As you can see V increases more rapidly than SA which creates a problem for the cell Side of CubeSurface AreaVolumeSA/V Ratio 1 cm 10 cm 20 cm

How cells and tissues increase surface area: – Protruding extensions Villi and microvilli in the small intestines for absorption of nutrients following digestion – Flattening the cell Red blood cells are flat which increases their SA to carry gases (O 2 and CO 2 ) Multicellular organisms increase their efficiency by having more cells, not by increases cell size

2.1.7 Multicellular organisms show emergent properties The organism can achieve more than the sum of what each cell could achieve individually Nerve cells (neurons) are not capable of thought but the communication and cooperation between the neurons make it possible for the brain to think

2.1.8 Cells in multicellular organisms differentiate to carry out specialized functions Every cell contains all the genetic material (DNA) but only a small portion of it is “turned on” or active ex. the cell in your toes has the information on how to make the pigment which colours your eyes, but will not use it Cells differentiate by expressing some genes (segments of DNA on a chromosome) and not others Genes that are not expressed are so tightly packed that they cannot be accessed Euchromatin = genes that are used or transcribed Heterochromatin= inactive genes

2.1.9 Stem cells are unspecialized cells An embryo’s cells are totipotent (they have the ability to become any type of cell) After many divisions the zygote becomes a ball of cells called a blastocyst- these cells are pluripotent (they have the ability to become almost any type of tissue) Cells from the umbilical cord are multipotent (they can become a limited number of particular types of cells)

Stem cells are different from normal cells: 1.Stem cells are undifferentiated. This means they have not yet specialized and all or most of their genes can still be expressed. 2.Stem cells are self-sustaining. They can divide and replicate for long periods of time.

Stem cells have the ability to differentiate when given a certain chemical signal Theoretically, you could make a stem cell replicate and then differentiate into liver cells and grow a new liver. In some countries stem cell research is restricted by legal measures: – Denmark, Spain, Sweden and UK- stem cell research is allowed using cells from embryos less than 14 days old – Only Denmark and the UK allow the creation of embryos for research purposes – 2006 President Bush vetoed a bill which would allow Federal money to be used for research where stem cells are derived from destroyed embryos

Outline one therapeutic use of stem cells Cell therapy= the therapeutic use of stem cells Most common cell therapy is bone marrow transplant to cure leukemia – Blood cells are produced in the bone marrow Also used in experiments to graft new skin cells for people with severe burns Another use is to grow corneas for people with failing eyesight Therapeutic cloning is very controversial and unacceptable in most cultures and religions

Let’s Clone Mimi Reproductive cloning g/clickandclone/ g/clickandclone/

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