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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. 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.





LuisanaT's picture

Lab was rather frustrating this time around

It is understandable that the students in this class all come from different scientific backgrounds and so it can not be assumed that concepts like osmosis/hypertonic/hypotonic/concentration gradients/etc to be common knowledge. But its irritating to find yourself as one of the few that aware of the answer to the "big" questions behind the ink dispersing in the different beakers or the onion cells undergoing inhibition. But its more agravating because you don't amount to anything with that. It felt so unfullfilling.


I constantly see our profs avoiding using the exclusive jargon associated with heavy duty science with good reason. We have come to understand, better said, memorize, how something happens and ignore why it is able to happen. Knowing the technical terms off of the top of our heads does not mean that we understand the topic at hand any better. Science is much simplier than that and so going into this the lab with a clean slate so to speak, allows us to actually grasp the story, not just the title.




Sharhea's picture

Onion Experiment (Shanika n Sharhea pt.2)

As we observed the experiment that Will performed, we saw man reactions. The color of one the cell membranes changed as time went by. *One drop of the salt: the purple is fading at the edges according to our view with the microscope*Second drop of salt: more of the cells continued to fade. The membranes located on the outer sphere faded first, probably because they got more of a direct contact with the salt first. The ones in the middle took more time to fade. One of the membranes totally faded out.*Third drop of salt and so on: fading at the same rate as the other twoGaps are created that allowed the cell membrane to pull away from the cell wall. Once we added water the cell membranes expanded *Salt water=shrinkage*Water=expandThe onion membranes behaved like a sponge. When salt water was dropped on it, it shrunk. When pure water was dropped on it, it expanded. Technically, we didn’t observe this ourselves but with Will’s experiment on the board.
ekim's picture

on the change of the onion cells.

Vivian Cruz, Saskia Guerrier, Eurie Kim

The onion layer on its own...
1) cell membrane
2) full purple coloring (from the purple skin/peel) within the membrane

When 1%NaCl (salt) was added to the onion layer...
1) the purple coloring along the rims of the cell membrane started pulling inwards
2) the more gaps started to form in the inner parts of the cell
3) little, tiny wrinkles formed along the edges of the cell membrane.

When distilled water was added back to the onion layer...
1) the gaps that formed in the inner parts of the cells started to slowly disappear
2) the purple coloring started to fill the cell again, but there is still a slight empty rim along the membrane

Our Story
At first, we thought the onion cells were making room for the salt, but it did not do the same for the distilled water, which means something in the salt is
causing the "shriveling"changes.
So then we think that the salt is drying up the water in the cells causing it to shrivel and create gaps within the cell membranes. These gaps would've been where the water was stored. Therefore, we believe that cells need water.

BUT we also think that the movement of the salt was too slow to move across the membrane, so that's why the cells had gaps along the walls for the salt (the salt was taking up space). On the other hand, the movement of water was fast enough to move across, therefore, refilling the onion to its almost-original state.

So what's the deal with the water molecule?

kcough's picture

Onion Cell Fun

Elizabeth Harnett

Kaitlin Cough

After we put the sodium solution under the slide, we could see white appearing around the membrane about 3 minutes later. Not all of the cells reacted this way: some of them showed no reaction to the sodium, whereas others were more affected. After about five minutes we put in a couple of more drops of the distilled water. This reaction was a lot quicker then the reaction with the sodium: in about a minute the cells already showed signs of "filling" up again and not show the white area around the cell. After about five minutes all of the cells were back to normal, the cells even looked like they were beginning to swell.

So why would the cell membrane pull away from the cell wall when the salt solution was added? It looked like the cell was being "deflated"-maybe it was losing water. The salt was sucking the water out of the cell, which meant that water can move in and out of the cell. The water was moving towards the area where there was a higher concentration of the salt. When we put the water back into the slide, the cell started to fill back up with water.

It seems that is was easier for the water to move in and out of the cell, whereas it was harder for the salt to move across the membrane. We can see that it was easier for water to move in and out of the cell because once we placed the distilled water solution into the slide the cells swelled almost immediately as opposed to when we placed the sodium solution into the slide. This took about three minutes for the water to leave the cell (we knew the water was leaving the cell because it was deflated).

Kee Hyun Kim's picture

Andy and Lakesha (part 2)

After finishing the first part of the lab, we proceeded to observe cell movements and how they diffeer when water and/or salt is added.

when we added 1 percent salt walter, the self membrane began to shrink and the gap between the cell membrane and the cell wall began to widen.

However, as soon as we added distilled water, the cell membrane began to expand again, filling up the gap between cell membrane and the water.

we think the shrinkage is due to the simple idea of osmosis. Osmosis is simply water diffusing from a highly concentrated area to a less concentrated area. (remember.. cell membranes are penetrable) this is why adding salt caused the cell membrane to shrink because it caused the water inside the cell to move out. (there is a high concentration of salt outside the onion cell and because of osmosis, water would flow out of the cell in attempt to balance the level of concentration)

Therfore, the cell becomes dehydrated and that is why a gap appears between the cell membrane and the cell wall and is again why this is reversed when we add distilled water.


Kee Hyun Kim's picture

Andy and Lakesha

We began the lab by observing the movement of color dye inside the water beaker. The pace in which the color dye was moving differed depending on the temperature of the water.

The beaker containing heated water moved the fastest, followed by the one in room temperature and the color dye in the cold beaker moved the slowest.

From this observation, we were able to come to a conclusion that the higher the temperature is, the faster the molecules move.

We than proceeded to observe movements of small plastic beads in water. The beads were different in size ( 2micron, 4micron and 8 micron.) We predicted that the smaller the beads were, the faster they would move since they are lighter and are therefore easier to be moved.

However, we had some trouble with our observations.



2 micron

30 micron

50 micron

4 micron

220 micron

350 micron

8 micron

350 micron

450 micron

The 2 micron plastic beads performed as expected ( each beads moved to different directions from where they started) however, we encountered a problem with the 4micron and 8 micron beads, both of them moved in bulk ( in a same wave of direction). Although we tried making different slides hoping to fix this problem, the 4micron and 8micron beads continued to perform in such manner and therefore it was impossible to make any meaningful observation.


kcough's picture


Elizabeth Harnett

Kaitlin Cough

2 micron beads:

5 trials, 1 minute trials, at the x40 objective

1st Trial: 4 units=10.4

2nd Trial: 19 units – messed up possibly because of microscope movement=49.4

3rd Trial: 3 units=7.8

4th Trial: 4 units =10.4

5th Trial: 4 units=10.4

Average: 6.8=17.68

w/o trial 2: 3.75=9.75

4 micron beads:

1st Trial: 5 units=13

2nd Trial: 2 units=5.2

3rd Trial: 1 unit=2.6

4th Trial: 1 unit=2.6

5th Trial: 1.5 units=3.9



The beads were moving much faster when we first set up the slide because they hadn’t settled. The smaller ones had a lot greater movement than the larger ones.

ekoike's picture

Crystal, Luisana and Eri

Crystal, Luisana and Eri


In the initial experiment that we conducted as a class, we observed the effect of temperature upon how the two drops of dye dispersed in the water. In the room temperature water, we found that the drops of dye slowly dispersed and began to move towards the bottom of the beaker. (It was concluded that this may have to do with the effects of gravity on the drops of dye themselves.)

In comparison to how the dye moved in the warm water, the drops of dye immediately began to disperse at a faster rate than in room-temperature water and change the color of the water and also, when we experimented with the cold water, the dye seemed to form a gel like structure. Therefore, we came up with a hypothesis that the temperature is a huge factor when considering how quickly and how wide something disperses.


Our observations:

2 microns: (30 seconds) 18.2 microns

4 microns: (30 seconds) 42 microns

(We were unable to observe the other micron-measure since the other two beads were sticking to the surface and couldn't be observed to be moving.)

Through our observations, we found that in the 2 microns slide, it was moving in a smaller concentrated area in comparison to the 4 microns slide, which was moving one general direction. We found that the larger the microns size, they covered more ground.


In this last portion of the experiment, we initially observed that there are cell membranes that adhere very closely to the cell walls of the onion sample when covered in distilled water.

Later, the more salt water we added, the more the cell membrane pulled away from the cell wall, leaving clear spaces in between as if they had shriveled. This was most visible in the cells with purple coloring.

Finally, when we pulled distilled water back across the slide and looked at the onion cells, the cell membrane appeared to have re-inflated and filled the space within the cell walls again without any gaps. Also, the color of the cell membrane seemed to have faded.

Previously we observed gravity, and different temperatures playing a part in causing the dye to disperse within the water. In this case, we observed the different solutions (salt water and distilled water) affecting the membranes within the cell walls. The introduction of the salt water appears to have drawn the water out of the cell membranes, causing them to shrink. When distilled water washed back over the onion sample, the membranes soaked in the water and appeared full once more, similarly completely filling the area within the cell wall.

cmcgowan's picture

beadylicious through a glass onion

In our class discussion we hypothesized that the smaller molecules would move more quickly, therefore moving longer distances in a controlled amount of time and the bigger molecules would move more slowly and therefore shorter distances.


In our investigation we gathered results that support our collective hypothesis. For each bead size we ran 2 trials for 30 seconds. We then calculated the averages for each size. The results are as follows:


2 microns: 34

4 microns: 26

8 microns: um, like...nothing. maybe 2.3.


In the second experiment, we tried to figure out why cell membrane moved away from the cell wall when NaCl was added and then why it moved back when water was added. Our story is that the NaCl opened the membrane so that the water could escape and since molecules are always moving the water left the cells and moved out to the paper towel because it was attracted to itself. It's so vain, it probably thinks this experiment is about it...

When we added the water back, the cell membrane expanded and moved out towards the cell wall. Molecules were moving so fast that the water didn't have a chance to move out once it got in.


ekim's picture

on the movement of microbeads.

Vivan Cruz, Saskia Guerrier, Eurie Kim

2-micron microbeads: 26.8 microns

4-micron microbeads: 43.3 microns

8-micron microbeads: 5.63 microns

*We started out with the hypothesis that temperature and size affect the movement/speed of molecule. The bigger the molecule, the slower the movement; the smaller the molecule, the faster the movement.

Although our data is inconsistent with our hypothesis in terms of size affecting speed, we think that the 4-micron microbead could have had an offset piece of data because only one of the three trials, the 4-micron microbead moved farther than the 2-micron microbead.

Sharhea's picture

Beads, Beads (Sharhea and Shanika)

At the beginning of class, we discussed how molecules may be dispersed throughout water. We tried different temperatures and observed how the blue dye dispersed throughout the water. With our observation, we assumed that due to the temperature of the water the blue may disperse more slowly and/or faster. In cold water, the blue dye dispersed slower than when it was in hot water or room temperature.

Movement: Sometimes the beads are vibrating or moving swiftly. Our data may be skewed due to the vibrations at one point and the swift movements at another time of observations. Observations for each Bead:


2microns - beads 2 microns-beads 4microns- beads 4microns -beads 8microns beads
Time 1min 2min 1min 2min 1min
Distance 12*2.6 =31.1micrometer 40*2.6 =104 micrometer 40*2.6 =104 micrometer 28*2.6 =72.8 micrometer No movement
Magnification 40x 40x 40x 40x 40x
Ruth Goodlaxson's picture

Ruth & Samar's Summary of Observations

We began with the observation that something caused the cell membrane to pull away from the cell wall when salt was added to a sample of onion cells. The center of the cell, in other words, shrank in the presence of salt water.

We had to think for a while about what could have caused this. It is our opinion that distilled water may pass freely through a cell, but salt cannot pass through a cell membrane. The water outside the cell is constantly in motion, in turn causing the salt particles to jitter. They pass through the cell wall, but are unable to permeate the cell membrane. They displace some of the space taken up by the cell membrane, causing the interior of the cell to shrink and expell some of its water. This explains why the size of the cell wall was not effected, but the interior of the cell was. Basically, the underlying concept seems to be that water can pass through a cell membrane but salt cannot.

Kendra's picture

Kendra and Ashley!

After observing how an onion membrane reacts when in contact with distilled water and with sodium chloride, we noticed that the NaCl pulled the membrane (cytoplasm) away from the cell wall. We think this is because the molecules of the NaCl are moving at a faster rate against the cell wall molecules than that of the distilled water, which caused the molecules of the cell wall to clump together in the middle.

Question: What would happen if we used a higher percentage of NaCl?

kgould's picture

Catrina and Kate Part 2

In the second part of the lab we were instructed to observe onion membrane cells. We took a small piece of membrane, placed it on a slide, applied some distilled water and looked at the specimen under the microscope.

We saw clear, rectangular cells with a light green border.

We then applied 1% NaCl and observed the result.

The cell membranes appeared to dissolve, drying out because of the NaCl. The light green border disappeared, leaving a faint gray outline of the cell, and an ugly shrunken form in the center.

Our explanation: the cells were dried out from the NaCl; the water moved out of the cell as the 1% NaCl was drawn into the slide. (The cells wanted to reach equilibrium with their environment, i.e. balancing the concentration of water and NaCl). As a result the cell membranes grew flaccid and shrank while the cell walls remained the same.

Questions: what would happen if you were to apply dye instead of 1% NaCl? Would you be able to observe the absorption of one substance and the expulsion of water? Does this experiment work on other plant cells? 

MarieSager's picture

Our hypothesis is that the

Our hypothesis is that the salt will explode the cells.

Observations: With the 1% NaCl the cells appeared slightly shrink. After reviewing this further, what ACTUALLY happened was the cell membrane moved away from the cell wall. This may have happened because the inside and outside of the cell were in equilibrium, and the addition of NaCl to the cells screwed up the equilibrium. In order to compensate, the cells expelled water and the cell membrane shrunk.

Further questions: What are the chemical make up of cells? And also, would
this be true of all cells? In answering this, one could use animal cells, human cells, and other plant cells.
Kendra's picture

Water Beads

From the demonstration Professor Grobstein did for our lab session, we came up with the hypothesis that since water molecules are moving constantly, small beads are more jittery than the larger beads.

By making slides for the microscope, we added water containing beads 2 microns, 4 microns and 8 microns big.

The slides containing 2 micron beads moved the fastest. Our fastest bead moved 15 micrometers in 2 minutes. When observing them, we could hardly keep up!

The 4 micron beads moved a little slower than the 2 micron beads and the fastest bead moved about 10 micrometers in 2 minutes.

Since the 8 micron beads were the largest, we found no movement at all. They simply stayed stagnant in the water.

Despite appearances, everything is moving constantly all the time. The larger the bead that we observed the less it moved and the smaller the bead, the faster it moved. Proving our hypothesis was correct.

Ruth Goodlaxson's picture

Ruth & Samar's Report

From the discussion, we hypothesized that the smaller microspheres would have a larger diameter of motion relative to their size than the larger micropheres, because the motion of the molecules would have greater effect on them.

Unfortunately, due to our difficulties with the microscpoe, we were only able to gather data for 2 micron beads. We measured the jitter of two beads, and found that their movement had a diameter of 26 and 20.8 microns. We didn't feel we could really draw conclusions from this data becacuse we have no point of comparison. However, it does support that water molecules are randomly moving.

MarieSager's picture

Observations: The


The 2micron--> jittered 20 microns

The 4micron--> jittered 11 microns

The 8micron--> didn't jitter!

So, the smaller spheres move faster than larger spheres and this is in line with our hypothesis.

A question for everyone: Does randomness really exist in science?

kharmon's picture

Jittery Beads Jittery Beads

Kerlyne Jean

Kyree Harmon

Based on our class discussion, we hypothesize that since water molecules are moving, small beads will jitter more than large beads. We observed 3 different sizes of spheres and 2 spheres within each size. For the 2 micron spheres, we observed movement in both, one for 28.6 microns and the other for 65 microns with an average distance of 31.2 microns. For the 4 micron spheres, we measure movement in only one sphere which was approximately 2.6 microns while the other sphere jittered without any forward or backward movement. In the 8 micron spheres we still observed 2 spheres but measured no movement for each.

The findings from our observations support our hypothesis. Because water molecules are moving and creating approximately the same force on each side of the spheres, the larger spheres did not appear to move as the forces cancel each other out. However, with the smaller spheres, smaller surface creates more chance for uneven force on each side, thus causing difference in force and visible movement.

Part 2

We continued this experiment with an observation of onion cells. When we added NaCl to the cells, the random movement of molecules was obviously stronger on one side than the other, pushing the cell membrane away from the cell wall and into the cytoplasm of the cell. Based on these observations, we wonder whether the random movements of the NaCl molecules are faster than those of water, which would cause the ueven movement of the cell membrane or a stronger force on just one side. We also question whether or not the size of the cell affects the speed of the molecules that affect it and whether or not the moving molecules "bump" the cell walls. Lastly, we wonder how whether other molecules of other chemicals move also and how.

kgould's picture

Catrina and Kate

In the first part of the lab, we observed the movement of a drop of dye within a beaker of water. The first beaker of water was at room temperature and the dye slowly expanded and moved through the water of, seemingly, its own accord. The second beaker of water was heated (to an unspecified heat) and a similar drop of dye was introduced. The dye expanded at a quicker rate through the heated water than it had through the water at room temp. A beaker of cold water (also of unspecified temperature) received a drop of dye and the dye moved very slowly through the water. (Actually, it still hasn't completely expanded through the beaker at the time that we're writing this, approximately 20 minutes after the dye was introduced).

It can be inferred from our observations that:

a) molecules are always moving randomly (hence the expansion of dye in otherwise "still" water)

b) the higher the heat of a substance, the quicker the random movement of molecules; the lower the heat, the slower the movement; therefore, the movement of molecules is directly related to temperature

In the second part of the lab, we were asked to observe "boats" in water, that is, the movement of small plastic beads (2 microns, 4 microns, and 8 microns) in relation to the movement of the water they rested in.

We observed three different sizes of plastic beads:

2 microns: these beads moved the most, moving 13 microns in 60 seconds.

4 microns: these beads move at a moderate rate, less than the 2 micron beads, moving 10.4 microns in 60 seconds.

8 microns: these beads moved the least at 2.6 microns in 60 seconds.

The beads moved in a jittery, random pattern, (they did not move in a directed path).

We developed a new hypothesis from these obervations: the smaller the bead, the more they were affected by the movement of the water molecules.

Water molecules are definately in constant, random motion-- that much is evident from the behavior of the plastic beads.