High School Biology-Chemistry SMILE Meeting
14 September 2004
Notes Prepared by Porter Johnson
We were all happy to see so many of our regular Biology /Chemistry SMILE family as well as some new members at our first meeting.

Pat Riley (Lincoln Park HS)
gave the first presentation of the year. Pat's first part was a nifty way to explain density. It involved three identical dark amber bottles (with lids), one of which was filled with cotton, one with water, and one with iron filings. Although all three looked identical from the outside (and had identical volumes), lifting (by Ed Scanlon) clearly showed that the masses (and thus the densities) were different, in both cases increasing in the order "cotton", "water", "iron filings".

Pat then showed a neat way to demonstrate the large heat capacity of water; this was done with ordinary (waxed paper) Dixie cups. Pat first showed that a Dixie cup will start burning easily when lighted with a match (we showed this first for the rim of the cup and later for the bottom; it works both ways). When the cup was filled with water, however, the lighted match would not set the cup on fire when held beneath the bottom of the cup; the water absorbed so much of the heat from the burning match (1 calorie/gm/degree C--the "specific heat" of water) that the paper could not reach a high enough temperature to ignite. The cup with the water did accumulate soot from the burning match on its bottom, which looked superficially like the result of burning, but closer examination showed that the cup with water did not burn. Excellent, Pat!

Roy Coleman (Morgan Park HS)
then gave us a demonstration of the new SMILE/SMART CD. This combines a huge number of SMILE presentations ("miniteaches") and SMART activities, as well as some really neat video clips of other science activities in one package. It is like having the SMILE and SMART websites on CD; this allows very fast/easy use of the SMILE/SMART resources without the requirement of an internet connection. The CD's are available from Roy for $10.

Ben Stark (IIT)
then discussed the genetics of sex determination in humans. Normal human males have the sex chromosome composition of XY, and females, XX. In human embryonic development, the default is development into a female. The Y chromosome contains a gene (SRY), which encodes the protein "testis determining factor" (TDF). At a certain point in development the SRY gene is turned on, and TDF is made. It causes the as yet undifferentiated gonads to develop as testes. The testes then secrete testosterone, which results in the development of other male specific characteristics. In the absence of TDF, the undifferentiated gonads develop into ovaries, which secrete female hormones, resulting in female development. Unusual XY individuals can be female if the SRY gene is missing or mutated. Unusual XX males have a piece of the Y chromosome containing the SRY gene "translocated" to one of the X chromosomes. XY individuals that lack a functional testosterone receptor cannot respond to the presence of testosterone and develop as females (although they have vestigial testes instead of ovaries and are thus sterile).

Notes taken by Benjamin Stark.