High School Biology-Chemistry SMILE Meeting
27 February 2001
Notes Prepared by Porter Johnson

Ben Stark (IIT Biology) Mendel's First Law
He asked about the inheritance pattern of the offspring with respect to red and yellow corn. He described the following experiment that he had done previously:

1. Take pollen from red and yellow corn, and place on corn silks of opposite type.
2. Wait for the seeds to develop on cobs, and see the results. All are red.
3. The first generation is then crossed, and their offspring examined at full development. Some are red and some are yellow, but not in the same proportion.
4. R gene (alleles)  Þ color (R: red or r: yellow) of kernel.
We conclude that R (red) is dominant over r (yellow). For every gene there are two copies per cell, so you can have RR (red), Rr (red), and rr (yellow).

Gametes have only one gene, but body cells have two  For gametes we have the following rules:

• RR Þ 100 % R
• rr    Þ 100 %  r
• Rr   Þ  50 %  R and 50 %  r

We represent the possibilities through the Punnett Square for the first cross:  RR ´  rr:

 First\Second r r R Rr (red) Rr (red) R Rr (red) Rr (red)

Now the Punnett Square for the second cross:  Rr ´ Rr:

 First\Second R r R RR (red) Rr (red) r rR (red) rr (yellow)

Thus, we expect the second generation to by 75 % red and 25 % yellow.  Actual results with 150 seeds:

 112 red 74.66 % 38 yellow 25.33 %

Pat Riley (Lincoln Park HS) Gas Laws
Non-Mathematical Part:

• She placed a plunger of a syringe on a convenient and simple setting, say 10 or 20, corresponding to a particular volume.  We predicted what would happen to the volume if we held our thumb over the opening and pushed on the plunger.  There was general agreement that the volume would decrease.
• Boyle's Law tells us that, as the volume of fixed amount of gas decreases, the pressure increases---where pressure is defined as  force per unit area
• Now we placed a hand on a piece of paper and traced its outline.  When we push on our hands, we are applying pressure only over the region traced on the paper.
Part involving some mathematics:
• Set a large syringe set at a volume of  100 cm3. Then place the tip onto a rubber stopper to make a seal.  We applied additional pressure by placing books on the stopper, measured the resulting volumes, and made the following table:
 Pressure (Number of Books) Volume (cm3) Inverse Volume (cm-3) 0 100 10.0 ´ 10-3 1 97 10.3 ´ 10-3 2 83 10.8 ´ 10-3 3 86 11.6 ´ 10-3 4 75 13.3 ´ 10-3 5 70 14.3 ´ 10-3
• Kinetic theory states that all gaseous matter is composed of particles that move randomly in straight paths until they collide.  They then bounce off in a new direction, until the next collision.  Collisions of the particles with the walls of the container produce pressure.  As you reduce the volume, there are more collisions with the wall, and hence more pressure.
• As you increase the pressure on the syringe, the gas particles become closer and closer together.

More mathematical part:

To estimate the absolute pressure of the air in the room, make a graph of  Pressure (Number of Books) versus the Inverse Volume (cm-3). The results will look like this
```
6  |
Pressure   |                                  *
# books    |                                *
3  |                              *
|                            *
|                          *
|________________________*_________
|    2    4    6    8   10   12   14  ´ 10-3
|                    .
|    1/V           .
-3 |                .
|              .
|            .
-6 |          .
|        .
|      .
-9 |    .
|  .
|.
-12 |

```
Atmospheric pressure [as measured in "number of books" on syringe] corresponds to the crossing point on the vertical axis; the vertical intercept,  or about 11 or 12 books.

Next presentation: Charles Law

Notes taken by Therese Donatello.