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Bio 103, Lab 3, Size Relationships: From Cells to Organisms

Paul Grobstein's picture

As you've discovered, scientific research can be done (and often is done) just by trying to make sense of the world around one, with that motiving observations that in turn lead to more specific understandings and new questions and hypotheses. Scientific research can also be done by using general questions and existing observations to shape a particular hypothesis that itself motivates new observations. Today's lab is aimed at giving you some experience with the latter kind of scientific research.

We know that multicellular organisms come in a variety of sizes but have in common that they are assemblies of cells. A general question that follows from this is "is there any relation between the size of an organism and the size of the cells that make it up?".

Your task today (in groups of two) begins with thinking of some possible general answers to this question, and about which ones make good (ie interesting and testable) hypotheses. You should then pick such an hypothesis and (using tools we will make available, including a microscope) collect relevant observations.

cejensen's picture

Emily Scioscia and Claire Jensen: Cells and Size

Going in to this experiment we assumed that all cells in living organisms were more or less the same size, and that it was the number of cells that corresponded to the size of the organism (large organism = more cells).

We first looked at a cross section of a worm, and second, part of a human's uterine lining. According to our initial thought/ our pre-experiment hypothesis, the worm and the uterus lining should have had cells the same size. When we looked at the worm cross section, we could see its complete boundary and the boundaries of its internal parts/organs. It was very difficult to see anything that looked like cells, though we knew we had to be looking at cells because living things are made of cells. On the 40 lens, we could make out many tiny brown-orange dots... but we still weren't sure. Then, we moved on to the uterine lining to compare. We immediately saw cells, or at least their nuclei through the 4x lens. As we zoomed in, we were able to see boundaries of cells-- the nuclei were dark purple and oblong/circular, and the cell membrane was a more elongated, transparent form surrounding it. We looked next at a part of a pig's kidney and found similar observations and cells of similar size to those of the uterine wall.

This changed our hypothesis. We now thought perhaps the cell sizes were different, but proportionally sized to the size of the entire organism/or proportional to its parts (i.e., looking at the full worm made it difficult to see the cells (assuming they were smaller) because its organs were smaller than, say, a human's or a pig's...).

To test this revised hypothesis, we compared a small plant (moss) to a larger plant (a pine tree).

We observed results that matched our hypothesis. The pine tree stem cross section, at 10xlens, we could measure/see about one nucleus per square "unit" (the space between the line for 0 and the line for 1) in the pine stem, but we could measure up to five nuclei in this same space for the moss.

As a side note, it was also slightly easier to see cells in plants because of their cell walls.

paoli.roman's picture

Fun with Microscopes


"I think the idea that big organisms have large cells and small organisms have small cells is valid."- Paoli

"I think all cells are the same size and that bigger organisms just have more cells."- Laura

Data/ Observations:

We both observed different sizes and shapes of cells. Trying to measure each organism was difficult since we both had different measurements (numbers) on our ruler.

1) Pine Tree-  36.6 microns
2)Laura- 63.3 microns
3) Pig- 7.3 microns
4) Earthworm- 10.6 microns
5) Moss- 7.6 microns
6) Algae- 33.3 microns
7) Fungus- 38.3 microns

We organized our data from largest organism to smallest however the cell sizes did not correlate. Both of our hypothesis were wrong since the size of the organism had nothing to do with the size of its cells and the cells in each organism were different from each other.WE HAD FUN! OUR HAIR IS THICK!

Yashaswini's picture

Michelle, Valerie, Yashaswini

We started with the hypothesis that bigger organisms do not necessarily have bigger cells, but instead, have a larger number of cells, that differ in shape and structure.
To acquire further information to prove/disprove our hypothesis, we decided to study the slides of the uterine lining of a human, the cross section of an earthworm and the jejunum of a pig.
The uterine lining of a human initially was a convoluted mess, at 4x. On magnifying further at 40x, we found it consisted of many, many elongated cells cluttered together, with only the nucleus of each cell visible in the form of a dark, round spot. We estimated the size of each cell to be between 3-5units, or between 7.5-12.5 u.
The earthworm‘s slide was actually a very, very interesting find: we found THREE different kinds of cells! The outermost cells were made conspicuous by a clutter of black dots, placed very close to one another. These cells were far too small for us to be able to measure them. The layer beneath this layer comprised of much larger, spaced-out, elongated, bubble-like cells (that resembled cheek cells a LOT) with very visible dark spots (nuclei) towards their boundaries. These cells varied from 5-10 units, or 12.5-25 u. The third category of cells was placed further below the second, bubble-type cells. These were horizontally elongated and had thin, hair-like structures jutting out. The nuclei of these cells weren’t visible very clearly.
Finally, the cells from the jejunum of the pig were similar to those from the uterine lining. They were initially wound up in a convoluted coil, which, on further magnification, revealed many tiny blackish dots, which we assumed to be the nuclei. We couldn’t see the individual boundary of these cells very clearly. The size of these cells varied between 2-4 units, or 5-10u.
We thus saw, that even though a pig is bigger than an earthworm, the size of its cells is smaller than that of the earthworm. Hence, we concluded that there is no correlation between the size of an organism and the size of its cells. We also understood that the shape, structure and size of cells in an organism differ according to their location of the cell and the function they’re expected to perform, as seen in the case of the earthworm.

Serendip Visitor's picture

in english!!!

i dont understand please use english!!!!!!!!!!!!!!!!!!

ktan's picture

cells-Kristel and Jesse

Hypothesis: Our hypothesis is that the size of the organism has no correlation with the size of the cells.  We believe this will be true because the size of an organism is dependent on its complexity, which involves layers of many cells, not a limited number of large cells.  Therefore, simple organisms could have larger cells than large organisms.

The following are measured in micrometers:

Uterus: 5
Pine Stem: 40
Jejunum: 17.5
Buttercup: 20
Gonium (4-cell colony): 100
Lumbricus (cross-section): 10
moss: 170

Conclusion: Using our data collected by measuring the different specimens, we found that the cell size and the size of the specimen appear to have no correlation, as we hypothesized.

sophie b.'s picture

sophie and keshia

Hypothesis: Bigger things are made up of small cells but small things are made up bigger cells

In the preliminary stage of our observations we thought that bigger organisms (i.e trees) were made up of small orderly cells, we looked at slides of five different organisms: a pine tree, a buttercup, fungi, algae, and moss. Our observations were as follows:

Pine Tree: 5-10 microns at 40x, smaller bounded circles, appeared to be more of a pattern, with little space in between cells.

Buttercup: Approximately 6.25 microns at 10x, also smaller bounded circles in a similar pattern to the pine tree cells.

Fungi: Approximately 5 microns, in long strands at 40x, spaced far apart from one another.

Algae: Cells were approximately 7 microns at 40x, individual cells in small groups, in a random arrangement spaced far apart from one another.

Moss: Cells were approxmiately 5 microns accross (the cells were too long to measure in height) at 40x, spaced tightly together.

We believe that our obervations support our hypothesis, as the larger organisms all had larger amounts of small cells, whereas the smaller organisms (ie, the moss) were made up of comparitvely bigger cells. Our observations may be skewed because we only compared plant cells, and not animals.


mcasias's picture

Lab 3

Heather Lewis and Mariah Casias

Hypothesis: After viewing some preliminary samples, we hypothesized that the size of an organism’s cells is inversely proportionate to the size of the organism. In other words, bigger organisms would be comprised of smaller cells while smaller organisms would be comprised of bigger cells.

In order to test our hypothesis, we viewed the cells of nine different organisms under a microscope and measured the size of the cells using units of micron. We then compared these measurements to the size of the whole organism on a meter scale.

Supporting Evidence: We observed that moss (usually measured in centimeters), had cells that were about 100 microns, which was a large measurement compared to our other data. Cup fungus (measured in millimeters or centimeters), had cells that measured around  150 microns. Pine stem cells were around 30 microns, while earthworm cells were 100 microns.

Refuting Evidence: Unfortunately the rest of our data refuted our original hypothesis. Pig intestine (m) cells measured at around 200 microns, and algae (mm) cells measured at 15 microns. Additionally, human uterus cells were around 20 microns each.

Conclusion: The evidence found appears to refute our hypothesis. The data would seem to suggest, in fact, that based on this particular data sample, there is no correlation between cell size and the size of the organism. Perhaps if the cell size of organisms is not dependent on organism size, then it is based on other criteria, such as quantity, function or location within the organism.


achiles's picture

Lab 3

Given the task of theorizing on the relationship between the size of an organism and the size of its cells, we hypothesize that there is none.
In order to carry out this experiment, we used a microscope to observe samples from several different organisms. We used eye piece scales 4x, 10x, and 40x to generally observe differences between the size, shape, color, and boundedness of cells within each sample. In order to create a uniform means of comparing cell size, we focused on the eyepiece with 40x objective. For each organism, we used the 40x eyepiece to measure the average cell sizes within each sample as denoted by the cell's diameter (length where appropriate). Our findings are as follows:
Buttercup: Average cell size: 62.5 micrometers
Algae: Average cell size: 12.5 micrometers
Pig Jejunum: (length) 275 micrometers

Human uterus average cell size: (length) 25 micrometers

Earthworm average cell size: (length) 75 micrometers

Pine tree average cell size (length): 50 micrometers

Moss average cell size (length): 37.5 micrometers

We believe that our diverse findings are without pattern and largely support our hypothesis that cell size does not correspond to organism size. We did notice some patterns, however, amongst our various cells. The plant cells, found in the Buttercup, Algae, Pine Tree, and Moss, were more distinguished (as they had walls around them) than were the cells found in animals. But, as stated before, we found no correlation between the average cell diameter in micrometers and the size of the respective organisms.


Anna Chiles. Debbie Chin


drichard's picture

cells and stuff

Our initial hypothesis was that cell size corresponds to organism size; in other words, a "small" organism will have smaller cells and a "larger" organism will have larger cells. Our hypothesis was obliterated as follows:

We observed five specimens in total:

Pig intestine: cell size ranged from approx. 2.5 - 40 microns at 40x magnification

Human uterus: cell size ranged from approx. 20 - 30 microns at 40x magnification

Worm: cell size ranged from approx. 10 - 15 microns at 40x magnification

Buttercup stem: cell size ranged from approx. 2.5 - 60 microns at 40x magnification

Prepared stem slide: cell size ranged from approx. 30 - 50 microns at 40x maginification


Basically, cell size has nothing to do with organism size. This is clearly exhibited by the difference in cell size between buttercups and humans. This fact combined with the high variability of cell size and shape within an organism pointed us to the conclusion that cell size is largely dependent on the specific function of that cell as opposed to the organism it belongs to.

Also, a note on plant cells: they are more clearly defined/ more easily seen because, unlike animal cells, they are bounded by cell walls.


-David R & Janice L

JJ's picture

Cell size and organism size

Hypothesis (and how we reached it):

Initially, we tried to come up with a hypothesis without looking at the slides, but Professor Grobstein told us that we should probably at least take a peek. Our hypothesis both before taking a look and after was: the size of an organism's cells is not relative to the size of the organism itself. We observed that while the cell size of each organism varied, never was the cell size relative to the organism's size. For instance, the size of a human uterine size was 250 microns, while the size of a moss cell was 360 microns. A human is a good deal larger than most patches of moss, so in this case, cell size and organism size were not proportional. Below are some of our other findings: (approximates)

Cell sizes in microns

Buttercup cell: 12.5

Uterine cell: 25

Kidney: 24

Pine stem: 28

Fungi: 37.5

Moss: 36

Worm: 8

Algae: 12


As our hypothesis was pretty broad, it would have been difficult to disprove it. Our observations were consistent with our hypothesis, but we also discovered that there is too much cell size variation in each organism to form a completely accurate set of observations.

-JJ and Lili

mfmiranda's picture

Week 3 LAB

When we frist began our lab we thought that the relationship that existed between organisms and their cells was proportional. We figured that if an organism was larger, it meant that its cells were also large. We looked at several different slides and compared our knowledge of what organism these came from to determine whether our observations supported what we had thought to be true.


The first slide that we looked at was the buttercup slide. We looked at it throught he microscope at many different settings. We didn't take notes and instead moved on to other slides. We continued to look at all the slides thoroughly, and realized that we couldn't take any real measurements of anything because the sizes of cells changed and so did their shapes. It was more difficult to compare cells to their organisms and to each other than we had previously thought.


In the end we gave up on measuring everything in a specific way. We realized that size wasn't proportional, and decided that size didn't have to be measured exactly. Perhaps we used our tools in a different way than the rest of the class. While others tried to assign specific number measurements to their cells, we decided that


We did however realize that our idea that a cell was proportional to the organism it came from didn't actually work. For example, the cells in the buttercup were larger than those in the human uterus. That didn't support our hypothesis since we know that a human is on a different scale than a buttercup. We also noticed that the pine tree also had smaller cells which again didn't seem to fit what we had predicted would happen.


Another problem with how we set out to make our observations was that we didn't think of all the differences that would inevitable be present. We only took into account the size of the organisms and completely ignored the fact that these organisms are completely different which meant that their cells would follow the same pattern. We found different shapes which meant that we couldn't just measure everything in the same way. I guess the biggest problem was how we were going to measure everything. We had to make choices about how we thought things were meant to be measured, but sometimes these choices set the cells even further apart. At the beginning we had taken some measurements and they fit into some sort of range. For example the buttercup was from 30-45 microns and the pine stem was from 10-30 microns. Still, although these were informative, figuring out our ranges was sometimes too complicated. In some instances we had to completely change the range just for a couple of cells. 


I guess in the end we ended up not really quantifying the cells. We ended up basing everything on just observations and not on exact measurements. Still, we did realize that our first thoughts about how big cells and their organisms are were off.


Maria Fernanda Miranda

Karina Granadeno

Terrible2s's picture

Lab 3: Cell Size and Organism Size

JPierre and Terrible2s

Hypothesis: The more complex an organism, the more levels of cells and therefore more cells that the organism will have.

We compared a few different organisms. These organisms included: pine-stem, jejunum ("pig organ"), moss, buttercup, and a human uterus during menstration. When we used the microscope on smaller organisms (or less complex), such as the moss and the buttercup, with an objective of up to 40 microns, we were able to see some of the smallest cell bodies within a larger cluster of cells that make up the organism. However, when viewing larger or more complex organisms such as the pig organ or the human uterus at 40 microns, we were not able to view in much depth. In fact at 40 microns, we were not able to see the smaller cells cells that make up the organism at all, but instead only a blob. Therefore, we believe that because a human organ  is a more complex organism (particularly in the case of the uterus), we would need a more sophisticated microscope to allow us to see it in higher microns to prove or disprove our hypothesis. From the tests we have done so far with our current equipment, our hypothesis has yet to be disproven. Yet, we do want to note that we cannot be completely certain of its "truth".

We would also like to note our experiences within the lab. Although we feel our hypothesis so far is strong, we did have trouble focusing the microscope lens at 40 microns and this could have led to a source of error in our data.

jmstuart's picture

cell size relative to organism size

Our research today was concerning the size of cells, and whether the overall size of the organism will indicate anything about the size of the cell. We looked at several different cell samples, including a buttercup stem, the cross-section of an earthworm, and the intestines of a pig. Our hypothesis was that the size of cells relates more to the function of the cell itself than to the overall size of the organism, especially in more complex plants or animals. We gathered the following observations:

Buttercup cells=60 micrometers

Earthworm=60 micrometers (lengthwise)

Unidentified small plant=65 micrometers (lengthwise)

Pig intestine=25 micrometers

Algea=15 micrometers


Our general conclusion is that there is no direct correlation between cell size and organism size, and that larger plants and animals are just more complex and composed of a greater number of cells rather than simply larger cells.


-Herman Marcia and Julia Stuart

Serendip Visitor's picture

problems doing research

It can be hard in some cases to identify cells (why easier in some cases? which cases?)

Cells come in different shapes, and in different sizes within one organism. How deal with those problems?

Good hypotheses are often developed only after making some preliminary observations. Is that cheating?