Reply to comment

Our hypothesis is that the bigger the size of the bead, the slower (therefore less distance covered) the bead will travel, and the smaller the bead, the faster (therefore more distance covered) the bead will travel.

The data results are as followed, as observed under X40, for two minutes:

2-micron bead: 7 micrometers

4-micron bead: 4 micrometers

8-micron bead: 1 micrometers

Based on the data of our experiment, our conclusion follows that of our hypothesis--the smaller the bead, the farther the distance it will travel, and the bigger the bead, the less distance it will travel. However, we want to point out that one factor that may have affected the outcome of this experiment is that the light in the microscope may heat up the slide, affecting the speed of the movement of the beads.

For the next experiment, we placed an onion skin under the microscope and added drops of low sodium water solution (0.1), and then we added drops of high sodium (0.25) water solution, and then added drops of purified water (no sodium). The results show the onion cells filling up with water when low (or no) sodium water solution is added. The cells look "fatter" and fuller, but when the high-sodium water solution was added, the cell walls "crinkled"--they sort of "collapsed" as the cells lost water.

Our explanation for why this happens is because when the no (or low) sodium water solution was added, the semi-permeable membranes of the cell walls in the onion skin allowed the water solution to enter. However, when the salt solution was added, the NaCl particles is bigger than the pores in the membranes of the onion skin cell wall, therefore it does not let the salt particles in, and even more important, the salt particles outside the cell wall will pull the water from the other side of the wall in order to equalize the concentration.