High School Biology- Chemistry SMILE Meeting
04 December 2001
Notes Prepared by Porter Johnson
Tyrethis Penrice (Oak Park Elementary) Behavior of Matter: Handouts on
Adhesion and Cohesion
Tyrethis led our discussion of these
Tyrethis then handed out two
worksheets, corresponding to each of these questions, and we proceeded to
investigate in groups. We noticed these things:
- Q: What happens when drops of water are placed on talcum
A: We suggested "beading up", absorption, and "clumping" of
- Q: What happens to the surface of water sprinkled with pepper when
detergent is dropped in?
A: We thought the pepper grains would move
away from the detergent layer.
- Drops did form beads which, after a few minutes, had a skin of talcum
powder on them. The beads formed only where talc was fairly thickly spread on
the paper. We may have been seeing cohesion of H2O to
H2O, talc to talc, or adhesion of talc to
H2O---or perhaps all of them. We would not expect the talc
to H2O interaction to be present, since beading occurs.
- Initially the pepper floats uniformly spread on the surface of the
H2O . The addition of detergent initially causes the
pepper grains to move away from one another suddenly (similar to "like charge"
repulsion?) and then to sink below the surface (loss of surface tension).
- In a third activity a glass was filled to the top with H2O
so that there was a "surface bulge" over the edge of the glass. A
cork was then floated on the surface. The surface tension kept the cork
near the center of the glass, far away from the edges.
Karlene Joseph (Lane Tech HS) Handout: Cell Diversitybrain, blood, muscle, skin, nerve, follicle, ...
started by asking "What types of cells are
Frana mentioned animal and plant cells. Inside
the human body we have these types of cells:
Activity: Karlene distributed clumps of clay of the same
volume. Each person took a clump and molded it into shapes corresponding
to the shape of a given type of cell. Here are some examples:
to a discussion of sickle cell anemia, thallassemias, etc, including "balanced
polymorphism" of the sickle cell allele. Even though the rr
individuals have sickle cell disease, rR individuals are more resistant
to Malaria than RR. In regions where Malaria is prevalent, the
rR individuals are the most fit of the three possibilities [rr, rR, and
RR], and this "balances" the presence of both r and R alleles
in the population.
- Skin Cells (flattened). This makes sense, because skin cells are
used as a cover.
- Muscle Cells (elongated): They contract and relax in the direction
- Red Blood Cells
- Normal (disc shaped; concave): R allele
- Sickle Cell (crescent shaped): r allele
This also led to a discussion of the sizes of various types of cells, which
vary (generally) from a few to a few dozen microns in diameter (1
micron = 1 mm = 10-6 meters). We
considered intrinsic limitations in sizes of cells in terms of the surface
area/volume ratio. We made "clay cells" of various shapes using our clumps
of clay. Then we measured the dimensions and calculated the surface/volume
ratios. [For example, a cube of side 2.5 cm has a surface area of
37.5 cm2 and volume of 15.625 cm3, so that
the surface to volume ratio is 2.40 cm-1.] Cells need to
be small so that the surface/volume ratio is large, so that cells are able
to absorb O2, food, and other nutrients at rates required to
support life. By contrast, large egg cells already have the nutrients
inside them, so that they are not limited so much in size. (For example,
consider ostrich eggs.)
Very interesting, Karlene!.
Mary Scott (Williams School) Handout: Air Power
Mary used a
small amount of air to lift a heavy load, to demonstrate the power of air.
She inserted a drinking straw into a 4-liter (gallon) size "zip-lock" bag, and
carefully sealed the opening with heavy-duty clear tape. She put the
deflated bag on the table, and put a rather heavy book on top of it. When
she inflated the bag through the straw, the book was lifted. She repeated
the experiments with several books on the bag, demonstrating the effect of
pressure of compressed air. The air blown into the bag becomes compressed, and
exerts enough (additional) pressure to lift and then support the books.
Good work, Mary!
Notes taken by Ben Stark.