Magnification and actual size Magnification = length of the image/ actual length of the specimen Actual size = size of image/magnification Use same units of measurement Scale bar shows the size of the line in the real specimen Actual size = Size of diagram (cm)*scale bar in micrometer/length of the scale bar in cm

Importance of Surface area /Volume ratio Limits cell size Limits cell size Rate of exchange of materials is dependent on the SA of the cell Rate of exchange of materials is dependent on the SA of the cell Metabolism (use of resources and production of heat and waste) depends on the volume of the cell Metabolism (use of resources and production of heat and waste) depends on the volume of the cell As cell size increases V increases proportionally faster than SA As cell size increases V increases proportionally faster than SA SA/V ratio gets smaller SA/V ratio gets smaller Lower SA reduces rate of exchange Lower SA reduces rate of exchange Higher V increases metabolic demands Higher V increases metabolic demands Rate of exchange can’t meet needs of metabolic demands Rate of exchange can’t meet needs of metabolic demands Sets upper limit on cell size Sets upper limit on cell size

Question Explain how surface area to volume ratio influences the cell size? Explain how surface area to volume ratio influences the cell size?

Cell differentiation Differentiation is development in a different way Differentiation is development in a different way In multicellular organisms cells differentiate into different types In multicellular organisms cells differentiate into different types Division of labour gives greater efficiency Division of labour gives greater efficiency All cells have identical DNA All cells have identical DNA Specialised cells have switched on some genes and switched off some others Specialised cells have switched on some genes and switched off some others The expressed genes produce proteins for its function The expressed genes produce proteins for its function Gene for insulin is active in pancreas cell not in retina cells Gene for insulin is active in pancreas cell not in retina cells Gene for rhodopsin is active in retina cell not in pancreas cells Gene for rhodopsin is active in retina cell not in pancreas cells Position of the cell, type of hormones, cell -to- cell signals etc influence how a cell deverlops. Position of the cell, type of hormones, cell -to- cell signals etc influence how a cell deverlops.

Question Outline differentiation in a multicellular organism Outline differentiation in a multicellular organism

Emergent properties Arise from the interaction of component parts Arise from the interaction of component parts The whole is greater than the sum of its parts The whole is greater than the sum of its parts Life itself can be viewed as an emergent property Life itself can be viewed as an emergent property Example : the human brain- individual neurons are not capable of thought but communication and cooperation between the neurons make it possible for the brain to think. Example : the human brain- individual neurons are not capable of thought but communication and cooperation between the neurons make it possible for the brain to think.

TOK: What are emergent properties? The levels of life – each level emerges from a level below. The levels of life – each level emerges from a level below. The pumping action of heart emerges from the interaction of the tissues in heart with chemicals and nerve impulses entering it. The pumping action of heart emerges from the interaction of the tissues in heart with chemicals and nerve impulses entering it. The complexity of life result from interaction of its various components. The complexity of life result from interaction of its various components. Question :Is life just a series of chemical and Question :Is life just a series of chemical and physical interactions without any purpose?

Stem cells These are unspecialised cells. They are different from mature cells These are unspecialised cells. They are different from mature cells They are undifferentiated, not yet expressed any of their genes. They are undifferentiated, not yet expressed any of their genes. With the right chemical signal they can be made to differentiate into specialised cells. With the right chemical signal they can be made to differentiate into specialised cells. Stem cells can be obtained from: Stem cells can be obtained from: -embryos -embryos -the umbilical cord and placenta -the umbilical cord and placenta -adult bone marrow -adult bone marrow They are described as : They are described as : -totipotent(can develop into any kind of cell) pluripotent(can become almost any kind eg :embryo) multipotent(many kinds) -totipotent(can develop into any kind of cell) pluripotent(can become almost any kind eg :embryo) multipotent(many kinds)

Therapeutic use of stem cells In 2005 stem cells were used to restore the insulation of neurons in laboratory rats In 2005 stem cells were used to restore the insulation of neurons in laboratory rats Stem cells could be used to replace body tissues such as heart valves and to treat diseases. Stem cells could be used to replace body tissues such as heart valves and to treat diseases.

Ethical issues and TOK -Involves the death of early stage embryos -Involves the death of early stage embryos -risks-stem cells may develop into tumours -risks-stem cells may develop into tumours - benefits :could reduce the suffering - benefits :could reduce the suffering Debate :pros and cons of stem cell research. Debate :pros and cons of stem cell research.