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

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.


Sharhea's picture

Micro - Explorations

Shanika Bridges-King

Sharhea Wade

We think that the larger the organism, the more cells it will have. We will use three plants: coleus, pine-stem, buttercup; and two animals: pig, human cheek cells.



Average Size

Coleus (medium)

Hairy, cactus shape @ 4x; Purple dots in the middle of blue walls (outlines) @ 10x; scales of a fish @ 40x

~38 microns

Pine-stem (big)

Multiple circle within a circular figure, multi-colored @ 4x; resembles an eye instead of brown eyes with black pupils, we have green eyes with pink pupils @10x; looks like a rainbow fish @ 40x

~ 20 microns

Buttercup (small)

Circular outer wall, inside filled with green space and a star-shaped figure in the middle @ 4x; more spacious than the other previous organism, the star is surrounded by a bunch of green spots @ 10x; more space between each cell

~109 microns

Pig (medium)

Shaped like an embryo with orange as the outside layer, and pink within @ 4x; @10x, we see the cells are much bigger and resembles a zebra but instead of black and white stripes, we see pink and white random stripes; @40x we could see the spaces between each cells

~46.6 microns

Human cheek cells (medium)

@4x small black circles with holes in them, resembling a black ring; @10x the cells are very spaced out and vary in shape and size, resembles blue crystals with black lines through it; @40x completely blue

~60 microns

Our initial hypothesis predicted that the bigger the organism, the more cells the organism will have. We proved this correctly because a small plant like a buttercup has very big cells, while a large organism like a pine has billions and billions of small cells.


andrelle's picture

Saskia and Luisana


There is a positive correlation between the size of the organism and the size of it's cell. The bigger the organism, the bigger the cell.


Organism Diameter at 40x (microns) Average Diameter at 40x

Coleus Stem Tip 26.0, 18.2, 26.0, 208 22.7

Buttercup 36.4, 70.2, 52.0, 44.2 50.7

Pine Tree Stem 13.0, 10.4, 13.0, 15.6 13.0

Paramecium 130.0, 156.0 186.0

Human cheek 13.0, 7.8 20.8

Sum of observation:

Through this lab our hypothesis has been proven wrong. From our observations we see that there is an inverse relationship between the size of the organism and its individual cell. The bigger organism had the smallest cell size, and vice versa.

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Using the Microscope

Crystal Reed

Eri Koike

Andy Kim

Hypothesis: We began our experiment with the prediction that there will be little correlation between cell sizes and the size of the organism itself. The reasoning behind such hypothesis was that organisms vary such greatly in size while there is little difference in the size of the cells; we believe that genetic information stored in DNAs play a bigger role.


Observations: (Big --> Small)

1. Human cheek sample (10 X) 50-80 microns

2. Jejunum (Pig Intestine) (40 X) 2.6-5.2 microns

3. Coleus (Stem Tip) (4 X) 26-65 microns

4. Pine Stem (4 X) 26-182 microns

5. Euglena (Protist) 20 -50 microns

6. Mixed Flagellates (40 X) 2.6 microns

Conclusion: We found that are hypothesis proved to be correct to a certain extent. The differences in cell sizes were huge, contrary to our prediction. However, little connection seemed to exist between the size of the cells and their parent organism. We found that organism size may have more to do with the complexity of the cells, as observed in both the pig intestine and the pine stem sample.


cmcgowan's picture

Rachel and Caitlin's Experiment: Hold Me Closer, Tiny Membrane

Hypothesis: There is no relationship between the size of an organism and the size of a cell, but rather, the amount of cells.

We tested our hypothesis by looking at various specimen and measuring the cells within each specimen. Here are our results:

1. Pinus-cells varied in size, with larger cells clustered in the middle. The cells generally ranged from 10-40 microns.

2. Coleus- no observable pattern of cell grouping. Average cell size was 30 microns.

3. Buttercup root- rounder cells ranging in size from 30-50 microns.

 4. Carolina- clumps of cells ranging from 40-50 microns

 5. Pig intestine- average cell was about 5 microns.

From this data, we have concluded that our story is a good one.  There seems to be no observable relationship between cell size and organism size. Each sample had cells of many different shapes and sizes. This diversity at the smaller scale perhaps reflects the diversity that we see in species as a whole.  However the reason for this will require further inquiry through observation, research, testing, questioning.

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Cell Size

Kaitlin Cough and Elizabeth Harnett

Before we started looking at the different organisms under the microscope, our hypothesis was "providing that the cells are the same size, the bigger the organism the more cells it will have." We believed that the cells would be the same size for the different organisms and there would be a direct relationship between the size of the organism and the number of cells. We observed seven different organisms: a buttercup, shark brain, pine stem, spirogyra, coleus stem tip, jejunum and Elizabeth's cheek cell.

Needless to say we quickly disproved our hypothesis. After looking at our first organism we realized that there were many different cells and were variable in size and color. There was no correlation between the size of the cell and the size of the organism. Below are our measurements for each of the organisms:

Buttercup: had two different types of cells, the outside blue cells (ground cells) were an average of 50 microns and the middle pink cells (vascular cells) ranged from 5.2 to 23.4 microns.

Shark Brain: all relatively the same size, purple in color, 2.6-5.2 microns on average.

Pine Stem: 4 different types of cells, the middle pink cells were 52 microns on average, smaller pink cells that were 10 microns, green outer edge cells were 38.2 microns on average and the small green cells were 7.8 microns on average.

Spirogyra: Small blue cells, 10.4 microns on average.

Coleus Stem Tip: Green cells with purple nuclei, 7.8-20.8 microns.

Jejunum: Pink cells, 2.6 microns

Cheek Cell: Blue cells, 2.6 microns.

After reviewing our observations the plant cells seem to be much larger than the animal cells. The animal cells are all about the same size: 2.6 microns.


vcruz's picture

cells vs. organisms

Vivian Cruz

Eurie Kim

All organisms have same-size cells, but have a different number of cells that determine the size of the organism.

Jejunum (pig) - 80 to 90 microns
Cheek cells - 70 to 80 microns
Coleus (stem tip) - 13 to 52 microns
Paramecium Caudatum (protista) - 130 to 182 microns
Pine stem - 13 to 52 microns
Buttercup root - 26 to 78 microns
Ceratium (protista) - 70 to 100 microns

Our story:
From looking at our observations, the smallest organism (protistas) had the biggest cells, the plants (coleus and pine) had the smallest, while the mammals (pig and human) had the middle range-size cells.
This shows that there is no correlation between cell and organism size.

kharmon's picture

The organism, the larger the cells.

Kyree Harmon

Kerlyne Jean

We believe that the larger the organism, the larger the cells that compose it. To test this, we collected 5 cell specimen, 3 plants and 2 animals. For each sample, we measured the largest cell and the smallest cell. The first sample was from Coleus. Its smallest cell was 5.2 microns and its largest was 31.2. Next we used Buttercup Root whose smallest cell was about 7.8 microns and largest was about 78. Then we observed the Pine Stem with a range of 13 microns to 52 microns. The first animal specimen was from a pig, whose smallest cells were about 2.6 microns and largest were 5.2. The last specimen that we observed was from Kerlyne's mouth and the cells there ranged from 2.6 to 5.2 microns. Based on our observations, we see somewhat of a correlation in our plant group. For the plant specimens, the larger the plant, the larger the smallest cells were. There was an upward trend for the largest cells, but they were not ordered. For the animal samples, both animals' cells were about the same size. More animals would have to be tested in order to make more accurate summaries concerning the size of the animal cells. However, our plant data seemingly supports our hypothesis. The difference in larger cell size can be attributed to cell growth and development and/or human error. It is still important to note that within each organism, there is a great variety of cell size and many more observations should be made and summarized.

Kendra's picture

Microscopic Adventures

Before Ashley and I made our observations, we came up with the hypothesis that the larger the organism, the larger the cells. There were an array of different types of organisms to observe, but we chose to use Protista/ Carolina Pendinium, Buttercup, Coleus, Pine Stem and Pig.

We soon discovered that there were smaller cells inside the larger cells and these smaller cells,in turn, sometimes had smaller cells. We both always thought that a cell didn't have smaller components. Since each larger cell had so many smaller ones, we measured the largest and the smallest cell and found the average. We used the micrometer scale located on one of the eyes lenses and at the 10x magnitude to measure the largest and smallest cell components. Here is a chart of the data we observed:

Organism Biggest Cell
Smallest Cell
Pine Stem
70 microns 20 microns
45 microns
Coleus 40 microns
5 microns
22.5 microns
Pig! 30 microns
10 microns
20 microns
10 microns
20 microns
15 microns
30 microns
10 microns
20 microns

We found that the size of the organism did not have any affect on the size of its cell. It seemed logical that the larger the organism, the larger the cell but when we looked back at our data, it showed that the largest of the organisms, the Pig, did not have an average as large as the Pine Stem, which is significantly smaller in size. Although we did not include data from the cells from Kendra's mouth, we quickly observed that those cells were significantly smaller than that of the pig, which was an interesting observation.

Ultimately, by reflecting on our observations, our hypothesis was proven wrong. The size of the cells does not have a direct correlation to the size of the organism.


Ruth Goodlaxson's picture

Ruth Goodlaxson and Samar Aryani-Sabet

We hypothesized that the size of an organism has no effect on the size of that organism's cell. We saw no reason to conclude that large organisms would have large cells, and suspected that large organisms simply had more cells.


Below, we list the largest and smallest cells evident in each organism. Organisms are listed from smalled to largest.

1. Protista: cells were 30 to 40 microns wide, and about 100 microns long.

2. Buttercup root: 20 to 60 microns

3. Coleus: 7 to 15 microns

4. Pig: 3 to 6 microns

5. Pine stem: 10 to 30 microns


The general trend we discovered was that smaller organisms possessed larger cells. This is true in every case except the pig, which is also the only animal of our samples and so has different cell structure. It warrants more investigation to discover if this pattern holds true for larger samples of both plant and animal cells. We would guess that in general, smaller plants have larger cells and larger plants have smaller cells.


However, it is important to note that there is a great deal of variety in cell size within an organism. This could be seen in various samples, such as the coleus, which had very small cells around the edges and larger cells toward the center of the structure. A better question than if larger organisms have large cells would be whether the role of a cell in an organism affects the size of that cell.


PS2007's picture

Cell Observation

Before we looked at cells under a microscope we hypothesized that the larger organisms would have larger cells. We looked at the cells of a Buttercup root, a pig cell, a Pine stem, a Coleus stem tip, and a shark brain cell.

By looking through the microscope we found that the Buttercup root cell was on average 30 microns across. The Pig cell was on average 7 microns across. The Pine stem cells averaged 25 microns across. The Coleus stem tip cell averaged 50 microns across. The Shark brain cells had a lot of variety, with many cells differing in shape and size. They were very small, on average 3 microns across.

Through our observations we found that the size of the cell is not proportionate to the size of the organism it comes from. We did not see a pattern in the cells that we examined but we would interested in examining more cells and trying to discover one. The shark brain cell really piqued our curiosity. It made us wonder if different parts of an organism have different kinds of cells.

Jen's picture

Jen Bonczar, Marie

Jen Bonczar, Marie Sager

Our initial hypothesis was that bigger organisms have bigger cells.

We observed five different types of cells, from all different sizes of organisms.

The smallest organism whose cells we observed was the buttercup root. The smallest sized cell was 20 microns in diameter, the largest was 50 microns in diameter, and the average was 35 microns in diamater.

The next largest organism was the pine stem. Results for the cells of this organism were approximately the same as the buttercup root, with cells being about 35 microns in diameter.

The Coleus plant, our next largest organism, had many different cell sizes. The sizes of the cells ranged from 25 square microns all the way to 1500 square microns.

Pig cells were approximately 7.2 microns in diameter.

Finally, we scratched some cells from the inside of Marie's cheek and colored them with a blue dye. We observed two specimens, one of which was about 50 microns in diameter with the second being 70 microns in diameter.

Currently, the observations allow us to construct the story that cell size is independent of organism size except for in the case of single cell organsims. This disproves our intial hypothesis. The pig cells we observed were much smaller than those of the buttercup root, yet a pig is much much larger than a buttercup root (pigs eat buttercups for breakfast). Also, organisms had many different sizes of cells, as is demonstrated in our observations of the buttercup root, pine stem, and coleus plant.

We also have a secondary hypothesis that bigger organisms have more cells, but this is an untestable hypothesis as we do not have whole organisms; thus we did not dwell on it in our observations. Still, it seems logical that bigger organisms would have more cells than larger ones simply because a larger organism has more volume of matter.
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Kate and Catrina

Our hypothesis: larger organisms are composed of larger cells, smaller organisms composed of smaller cells.

Our observations:

  • coleus: cells average 40 microns
  • buttercup root tip: cells average 50 microns
  • pine stem: cells average 20 microns
  • pig: cells average 5.2 microns (large size difference between cells)
  • protist (mixed flagellates): cells average 60 microns (there is a large size difference between each flagellate)
  • spirogyra vegatative: average 60 microns
  • protist (ceratium): average 100 microns

Our conclusion: the size of an organism does not itself determine the size of its cells. Larger organisms do not have larger cells than smaller organisms. On the contrary, the single-celled protists had the largest cells at 100 microns (ceratium), and the portion of pig intestine had the smallest cells at 5.2 microns. The pig is much larger than the protist. Perhaps it is not the size of the cells that matters, but the quanitity of cells when it comes to the size of the whole organism.