Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

Bio 103, Lab 4, Very small space/time scales: randomness as a first mover?

Paul Grobstein's picture

Our broad objective today is to make sense and explore the implications of a remark about small scales by the physicist Erwin Schrodinger in a classic book called What Is Life? published in 1944.   Schrodinger asserted that underlying all order is random motion.  Is that so, and, if so, how does order emerge?
The activity falls into three parts. The first we will do and discuss together. From it will emerge an hypothesis about water that groups will attempt to test with relevant observations on Brownian Motion (movie). A summary of your observations and the conclusions you draw from them should be the first part of your lab report. Your group will then be asked to make an additional set of observations, and try and come up with an hypothesis to account for it that draws from the first two activities in the lab. The second part of your lab report should include a summary of your observations, the resulting hypothesis, and a suggestion of a set of new observations that could be used to test it.
(For more on randomness and order, see Evolution/Science: Inverting the Relationship Between Randomness and Meaning).  

ktan's picture


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.

ED's picture

Brownie points

Emily Scioscia and Claire Jensen
I.                    Initial class hypothesis: smaller things move faster, so perhaps the smaller beads will move more quickly.
II.                  Summary of observations:
All measurements were taken at 40 x lens.
2 microns bead: moved 4um (4 units on ruler) away from starting point over one minute. We did this twice, and got the same distance both times.
4 microns bead: in one minute, it moved 70 units “down,” and approximately 20 units to the left of the ruler (it started “on” the ruler at 100) – but not only did it move “down,” it also went out of focus, which means it move up or out.
8 micron bead (courtesy of Paoli’s microscope set up): moved .5 (x2.5) microns in one minute.
*Because our initial data set for the 2 micron beads did not support our hypothesis, nor the matching trend that our 4 and 8 beads reflected, we decided to retest the 2 micron bead just incase…
Our results: this time, our 2 miceron bead moved 28 units, and became significantly out of focus.
III.                Conclusion: While our retesting of the 2 micron bead did not perfectly match up with the class’ initial hypothesis (that the small bead would move fastest), we can account for error in that we had no way of measuring how far “up” or “down” in the water the bead being watched moved. We also should consider that the heat of the light may have varied, depending on how long it had been on and how bright we had it.
IV.                Onions!
Thinking out loud/conclusions:
Ok. The salt makes the membranes of the cells shrivel/implode, seeming to suck something out. The water expands them back to their rounder, fuller, normal size. This seems to be caused by the cells absorbing the water. Water molecules are a little bigger than sodium molecules… Water doesn’t have a charge, but sodium has both a negative charge and a positive charge. A minimally possible thought (though judging by will’s behavior, we don’t think he thinks charge really matters in this):
Membrane is semi-permeable, and it is lipid-y. Water isn’t supposed to be able to permeate fatty membranes (ie oil in water), but eventually it does.. the fat and the water tend to separate… yet the water easily was being re-absorbed into the cells when water was added again after the salt had shrivled the membrane up (the membrane was within the cell wall…).
In the previous “beads” experiment with water, we hypothesized and for the most part, found to be true, that smaller molecules/things move faster. Since an NaCl (sodium) molecule is slightly smaller than an H2O molecule, we can hypothesize that the sodium moves faster than the water. This still doesn’t explain the effect of the salt on the membrane (zig-zaggy implosion) vs the effect of the water on the membrane (expansion/rounding out).  We are also attempting to relate the look of these lines (zig-zaggy vs. rounded out) with the initial experiment today: three beakers of water, one cold, one medium temp, and one hot--- each had blue dye added. The blue dye totally spread/evened out in the hot water beaker, and kind of froze/stayed in random swirls in the cold one. Temperature indicates amount of energy present (hot = more energy). The salt molecules had “zig-zaggy” lines like were stuck in the cold water—but moved around more like the molecules in the hot water….
No grant money for us. To be continued (maybe).

xhan's picture


Hypothesis: the bigger the micron the slower the movement.
2 microns:
10 micrometers per minute
4 microns:
2 micrometers per minute
8 microns:
Movement too slow to detect (per minute?)
Conclusion: conclusion matches hypothesis

1% saline solution: normal-looking cells
25% saline solution: heavily shriveled cells. Looked like small, sharp fragments of broken glass.
Distilled water: returned to normal brick-like cell shape, maybe a little larger.

Observations: when we added the water we moved the slide from left to right following the movement of the water and observed the changes in the cell sizes/shapes.
When we added 25% salt solution(NaCl), the cell membrane tended to shrink, because the salinity of the solution outside the cell was higher than the liquid inside the cell, thus the water on the inside diffused to the outside(high concentration to low concentration). When we added distilled water, the cell membrane expanded because the concentration of water was higher on the outside as opposed to the inside, so the water diffused to inside.

lcorhan's picture


In discussing the idea of movement and diffusion, Paoli and I (Laura) predicted that substances diffuse faster depending on their movement. We believe that increased energy causes increased movement and in turn allows for a faster diffusion process. Also, we think that the smaller the particles the less energy will be needed for maximum movement. Therefore our prediction is that the best conditions for maximum diffusion are small particles and a lot of energy.

When looking at the micron balls, we discovered our hypothesis to be true! The 2 micron balls moved the fastest then followed the 4 microns and lastly the 8 micron balls.

Our Data:

all observed at 40x under microscope

2 micron balls - move somewhat fast, there is shifting within the liquid, wiggle in place and then in a circular motion

4 micron balls - clumpy, moving somewhat faster than 2 micron however hard to REALLY tell

8 micron balls - very separated, moving extremely slowly.


At the beginning of this experiment both Paoli and I we very discouraged and frustrated: WE COULDN'T SEE ANYTHING BESIDES CELLS!!! However, once Will put the slide on the projector, we started to notice the cells reacting to the water and the sodium chloride mixture. We observed that by adding water to the slide, the onion cell's sac absorbed the water and expanded. When we added the the NaCl solution to the onion slide, we noticed the cell's sac "dried" up and looked crinkled.

We know that when NaCl is diffused in water it "breaks" apart into positive Na ions and negative Cl ions. We decided that ions don't exist long by themselves due to their charge. The charge makes them "attractive" and "attracted" to other atoms and molecules. H2O is the only other atom in the solution, so we decided that the ions start a type of bond or some such thing to "absorb" the water molecules making them no longer just H2O. We think that the ions actually take the water molecules from the cells, essentially "burning" them and making them "crinkled". Although this was witnessed in regards to the cell's sac, we didn't notice an effect on the cell's wall.


jmstuart's picture

brownies in motion

Phase 1: In search of Brownian Motion we observed plastic beads of three sizes (2, 4, and 8 microns respectively) for two minutes under 40X power. We completed three trials for the 2 micron beads and two trials for the 4 and 8 mircon beads. The average movement is represented below:

2 micron beads: about 7.67 microns.

4 micron beads: about 5.625 microns

8 micron beads: about 2.5 microns.

It should be noted that, during our calculations, we omitted a fourth trial of the 2 micron beads as we determined it was not representative of the general motion of the beads (during this trial a bead was observed to move 75 microns. Though this would have further proved Brownian Motion, the finding was an outlier).

Phase 2: During this portion of the lab we observed the changes in an onion cell when is was immersed in .1% salt water, 25% salt water, and distilled water. It was observed unanimously that the cell membrane of the onion cell shrunk away from the cell wall when immersed in 25% salt water. This pattern points to a very NON-random movement of molecules (which contradicts the earlier findings of the lab). However, in the same way that temperature seems to influence the movement of molecules, the concentration of a particular solute can dictate how a group of molecules will move. In this case, the salt concentration gradient over the cell membrane (less salt in the cell, more salt outside of the cell) caused the water to move out of the cell so as to maintain equilibrium (as the cell membrane was impermeable to salt) - that is, the water left the cell so that the water to salt ratio was equal inside and outside of the cell. In this case, equilibrium seemed to take precedence over random movement.

One way to test this theory of equilibrium influencing the random movement of water molecules would be to use a dialysis bag manufactured to be impermeable to molecules larger than water. By filling a dialysis bag impermeable to glucose with water, and placing it into a solution including glucose, we could observe the movement of water by taking a measurement of the weight of the bag before and after exposure. This experiment would establish whether movement of water molecules could/would be directionally dictated by a solute concentration gradient over a membrane.

This process of equilibrium, like evolution (discussed in class today) is a blind process, devoid of intention.


Julia Stuart and David Richardson

achiles's picture

Lab 4: Anna and Kalyn

The following report is on an experiment involving testing Einstein's theory of Brownian Motion using microspheres in water. Upon beginning testing Einstein's theory, we hypothesized that the smaller the diameter of the microsphere (2 microns, 4 microns, or 8 microns), the higher the degree of movement the microspheres will have in the water. Our findings support ours and Einstein's hypotheses.
The microspheres with a diameter of 2 microns, when viewed under an objective of 40x, were seen to move in a vibrating motion at a fast pace. Some moved a small distance from their original positions.  
The microspheres with a diameter of 4 microns, also seen at 40x, were visibly moving bu only at a slow "floating" pace.
The microshperes with a  diameter of 8 microns, seen at 40x, were almost stationary.
In conclusion to part A of the experiment, all empirical evidence suggests that Einstein was onto something with his theory of Brownian Motion. The randomly moving water molecules do, in fact, move the microspheres at a similarly random pace. The smaller the microspheres (and the mass the water molecules have to move), the faster the pace at which the body moves. 
  In part B of this experiment, we observed the effect of water and salt, hydration and dehyration, of the skin of an onion, which is approximately one cell layer deep. We observed the skin in 3 different solutions: distilled H2O, NaCl (1%), and NaCl (25%). Each solution represented a different concentration of salt: 0%, 1%, and 25%. Using the microscope, we made observations regarding the structure of the cell in each solution. The following is a summary of our observations:

In the low concentration (1%) of NaCl, we observed the cell membranes increasing in size.

In the higher (25%) concentrated NaCl, the cell membranes exhibited an apparent "shrinking." The cell walls, however, stayed put.

In the distilled H2O, the cell membranes swelled again.

The first observation we made in class consisted of water's interaction with dye. By altering the temperature of water the dye interacted with the water's molecules at different rates depending on the water's temperature. The skin of the onion when interacting with either salt or water generated a swelled or shrunken cell membrane.  When submerged in H20, the cells swelled because water was entering the cell. When submerged in the NaCl (especially higher concentration, the cell was dehydrated and water left the cell, producing a shrunken membrane.

For every reaction, there is an equal and opposite reaction. Perhaps it is because there are more salt molecules to bump against the cells of the onion skin, the cell membrane shrinks to form a stronger barrier.

A way to test this would be to heat up the 1% NaCl before adding it to the skin of the onion. Because the temperature of the solution would increase the speed of the movement of the water molecules, perhaps the cell membrane would react more strongly and shrink at a greater rate in order to "protect" itself from the salt molecules.

JPierre's picture

Lab 4-Jennifer Pierre, Karina Granadeno, Maria Miranda

These are our observations with an objective of 40x

2 Microns
1st time: 30 micrometers
2nd time: 20 micrometers

Here there was a lot of movement and it was difficult to measure and we kept trying to average it out.

4 microns
1st time: 3 micrometers
2nd time: micrometer

Here, we barely saw any movement and it was hard to tell if they were actually moving or if we just assumed they were.

8 microns
1st time: <1
2nd time: 0

Here we were unsure if there was any movement at all. We ended up wondering whether it was moving but it was too difficult for us to actually see the movement because it was so slight.

Onion Peel Observations

1% salt water:

There was no movement. There were cells that were almost rectangular, like long boxy blobs. Inside of them there were tiny dots. We didn't see anything that was moving inside the cells and the cells themselves weren't moving.

25% salt water:
Now we see the cells but instead of dots inside of them, there is something bigger in the middle of them. We are seeing more than just the cell wall. This is apparently the cell membrane, which has now pulled away from the cell wall and is now more apparent.

Distilled water

With the distilled water the cell is no longer shrinking but is instead expanding.


Overall we hypothesize that the size of the particle AND the density of the water play a role in the movement of the particles. For example, the first half of the lab we observed that the bigger beads moved much less than the smaller beads in distilled water. This is because the distilled water (being less dense) was randomly moving however, it was not strong enough to move the beads that were much more denser.

In the second half of the lab, we observed that in 1% salt water, the cell membrane of the onion seemed as if it were attached to cell wall (to the human eye). However, when the water was made more dense after an increase in the amount of salt to 25%, the water was able to detach the cell membrane from its cell wall and move it (albeit a small movement) towards the center of the cell. When the onion was tested in distilled water, the cell membrane reverted to being attached to the cell wall again. This is because the water being less dense was not a strong enough force to pus the cell membrane away from the cell wall, therefore the cell membrane remained attached to the cell wall.

dchin's picture

Onion Membrane

Janice, Debbi, Lili, JJ

Why are the changes happening? 
One story we decided on was that the saltier water contains more molecules that push against the cell membrane more, forcing the membrane to contract, as if it were a phalanx protecting Spartan warriors.  The wall is permeable, letting water come in and push on the membrane. With the added pressure of invading salt molecules, the membranes must contract and protect the inner "Spartans" from the invading "Persian" salt water.  With distilled water added, the Persians were defeated, because there was less pressure pushing on the membranes because the Athenians came to aid. Then the Spartans were liberated.

The end.

mcasias's picture

Onion cell observations


Heather and Mariah
We think that the change in the cells occurs from the diffusion of water across the cell membrane and into or out of the cell. When the cell is in a .1% salt solution, the membrane is filled with water. When this is replaced with the 25% salt solution, the water wants to move to the area with more salt so that it is reduced to the same concentration as within the cell.  Brownian motion explains why this water is in motion and thus able to pass out of the cell. When the distilled water is introduced, the water wants to move back into the cell and so the membrane fills back up with water and the equilibrium between the cell and its surrounding water is restored. We think an additional way to test this idea would be to measure the amount of salt present within the cell while it is immersed in different solutions and see if there is a connection between what the cell looks like and how similar or different its salt level is to that of the surrounding solution.


hmarcia's picture

Onions Observations

In the first part of lab, we observed that water bumped into the beads and forced the bead to move (thus proving Einstein's Brownian Motion Theory).  In the second part, we saw the effects of Brownian Motion on an organic entity.  We observed that an onion skin in .1% salt water had rigid cell structures with free-flowing membrane cells.  When placed in 25% salt water, the onion cells appeared to have a shriveled membrane in its center.  When placing the onion cells in distilled H2O, we observed that the onions cells went back to a similar composure like the onion cells in .1% salt water.

When the combining the first part of the lab with the second part, we are able to theorize that the water molecules bump against the salt molecules, which in turn bumps into the onion cell's wall.  This in turn pushes the cell wall closer together, giving it a shriveled appearance.  From this information, we can conclude that the lesser the quantity of salt, the greater the movement of the onion cell's membranes. 

To test our hypothesis, we simply replace salt with other molecules, of similar size of course, and redo the same experiment and see its results. 

-Halima and Herman

mcasias's picture

Bead Observations


Heather and Mariah
2 micron beads: 20 µ of movement over two minutes
4 micron beads: 12.5 µ/ 2 minutes
8 microns beads: 15 µ/ 2 minutes
Our observations show that the 2 micron bead moved faster than both the 4 and 8 micron beads. The 8 micron bead moved faster than the 4 micron bead so we cannot say that this evidence supports Einstein’s theory or refutes it. However, the difference in movement between the 4 and 8 microns beads is smaller than the difference between the 2 and 4 micron beads so further observations could provide evidence in support of his theory.


dchin's picture


Debbi and Janice

We conducted two trials for each bead measurement of 2, 4, and 8 microns, observing each for two minutes at a time. The first time we observed the 2 micron beads, there were 26 units of movement, meaning that it moved 65.0 microns. The second time we observed it, there were 17 units of movement, meaning that it moved 42.5 microns. The first time we observed the 4 micron beads, there were 16 units of movement, meaning that it moved 40.0 microns. The second time that we observed it, there were 8 units of movement, meaning that it moved 20.0 microns. The first time we observed the 8 micron beads, there were 10 units of movement, meaning that it moved 25.0 microns. The second time that we observed it, there were 5 units of movement, meaning that it moved 12.5 microns.

Our observations were consistent with Einstein's theory. The amount of movement decreased as the molecules got bigger. We attribute the decrease in movement between the first and second trials to the cooling of the water.

dchin's picture


Debbi and Janice

We conducted two trials for each bead measurement of 2, 4, and 8 microns, observing each for two minutes at a time. The first time we observed the 2 micron beads, there were 26 units of movement, meaning that it moved 65.0 microns. The second time we observed it, there were 17 units of movement, meaning that it moved 42.5 microns. The first time we observed the 4 micron beads, there were 16 units of movement, meaning that it moved 40.0 microns. The second time that we observed it, there were 8 units of movement, meaning that it moved 20.0 microns. The first time we observed the 8 micron beads, there were 10 units of movement, meaning that it moved 25.0 microns. The second time that we observed it, there were 5 units of movement, meaning that it moved 12.5 microns.

Our observations were consistent with Einstein's theory. The amount of movement decreased as the molecules got bigger. We attribute the decrease in movement between the first and second trials to the cooling of the water.

hmarcia's picture

Observations of beads

After observing three different size beads, we conclude the Einstein's theory is valid and that size is a factor in the velocity of the object.  We found that the bigger the bead, the less distance it covered during our two mintue observations.


2 micron beads moved a distance of 12.5 microns.

4 micron beads moved at a distance of 7.5 microns.

8 Micron beads moved at a distance of 2.5 microns. 


-Herman and Halima

JJ's picture

bead observations

Lili and JJ

We observed the beads moving in the same pattern that Einstein stated: the 2 microns moved the most, the 4 microns moved some, and the 8 microns very little. The 2 micron in diameter beads moved 247.5 microns. The 4 micron beads moved at 10 microns. The 8 micron beads moved at 2.5 microns.  We repeated the procedure but found that none of the beads moved at all, so did not include this data. From our observations, it appears as if Eistein's statement was correct but we cannot be sure because we only collected one "legitimate" set of data.