BIOLOGY 103
FALL, 2003
LAB 3
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| BIOLOGY 103 | |
Scientific research can also be done by using general questions and existing observations to shape an 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 that they all 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.
Your report should include a brief description of your hypothesis and of what motivated it, an account of your observations, and a conclusion in which you discuss the significance of your observations for your hypothesis.
Hypothesis:
If two organisms (regardless of their size) belong to the same species, then their cell sizes will be similar.
Motivation of Hypothesis:
Common sense told us that all cells are not the same size. For example, an ostrich egg is one complete cell while an amoeba is also one complete cell but of significantly smaller size. But within the same species if size differs, then the quantity of cells may differ but the size of the cells which actually make up the organism does not differ.
Observations:
(Human)
5'7" --> 10x = 7 um/OR
5'5" ---> 10x = 7 um/OR
(Maple leaf)
4" --> 10x = 2 um/OR
1.5" --> 10x = 2 um/OR
(Clover leaf)
1/2" --> 10x = 1.5 um/OR
1/4" --> 10x = 1.5 um/OR
(Mushroom)
3/4" --> 10x = 3 um/OR
1/2" --> 10x = 3 um/OR
Conclusions:
From the small sample of organisms we investigated we have concluded that our hypothesis is correct; as long as the specimens are within the same species their cell sizes are the same. However, within our sample of organisms cell sizes proved to differ between species relevant to the organisms' size (i.e. Humans over 5' tall, 7 um; clover leaves smaller than 1", 1.5 um).
Problem: Does the size of cells depend, relatively, on the size of the overall organism?
Hypothesis: Cells occur in a size range which varies according to the size of the multicellular organism. For example, human cells will be bigger than moss cells.
Observations (in microns)
Algae: 40—60
Cheek cell: 30—50
Trachea cell: type 1: 1—2
Type 2: 3—7
Worm epidermis: ~ 350
Moss globule: 30—50
Moss strand: ~10
These observations indicate that cells do not occur in a size-relative relationship. For example, while the earthworm as a whole organism is smaller than a human, the human cheek cells are smaller than the earthworm epidermis cells. However, we must keep in mind that we only sampled a specific type of cell for each organism. There are many different types of cells. For example, of the two moss cell-types sampled, one type was 10 microns in length while one was 30—50 microns. We must modify our hypothesis to say that not only do cells not vary in size relative to their greater organism, but cells within a certain-sized organism come in many different shapes and sizes, each different, none relative to the overall size of the organism.
Data:
Algae:
- cell #1: 26 um (@ 4x)
- cell#2: 72 um (@4x)
Human Cheek:
- cell #1: 5.2 um (@40x)
- cell #2: 5.85um (@40x)
Human Spinal Cord:
- cell #1: 1.82 um (@40x)
- cell#2: 2.6 um (@40x)
Earthworm:
-cell#1: 13 um (@40x)
- cell#2: 14.3 um (@40x)
Based on our observations it seems that our hypothesis may not be correct. From the size of the cells measured, it appears that smaller organisms have larger cells, which means that from the size of the cells you can estimate the size of the organism. Perhaps smaller organisms have fewer, larger cells than larger organisms, which have many small cells. In other words, "size does matter".
Larynx cell = 18.2 micro meters
Spinal cord cell = 13 micro meters
Moss cell = 150 micro meters (50 micro meters in width)
Earth worm cell = 39 micro meters
Buttercup cell = 48.2 micro meters
Based on these observations, our original hypothesis was proven wrong. For instance, an earth worm is generally smaller than a human, however its cells were found to be larger. In addition, in each sample we found cells multiple sizes, colors and shapes - the measurements were taken from the clearest areas of vision. This leads us to a more important point - different organisms have different kinds of cells, (in humans, for example, the larynx cells differed significantly from the spinal cord cells). We can suggest, from our observations, that the link between size of an organism and the size of its cells is more arbitrary than we orginally hypothesized. Perhaps if we compared corresponding cells in organisms, such as a human spinal cord cell to a dog's spinal cord cell, we might get closer to finding a relationship concerning size. However, these correspondences are not often present, because plants have no spinal cords, for instance, so we would be required to find a different method of comparison.
hypothesis: The greater the size of an organism, the greater the size of its cells.
Observations:
- Humans:
cheek cell: average size = 70 microns
vein cell: average size = 46.8 microns
spinal cord cell = 57.2 microns
- Elodea:
between 19 and 27 hash marks (X40)
average cell size = 241.8 microns
- Wild Algae
between 14 and 19 hash marks (X40)
average cell size = 174.2 microns
Conclusion:
There is no absolute relation between the size of an organism and the size of the cells that constitute it. As we observed earlier, the elodea's average cell size is larger than that of the human's. We also observed that cells within one organism are approximately the same size.
Hypothesis: The smaller the organism, the smaller the cell. We felt that the most obvious way of trying to make relationships between these different organisms is to begin by making size/cell comparisons.
Observations:
Romina's cheek cell:
4x--104 mm/or
10x--70 mm/or
40X--65 mm/or
Description: Small, oval
Paula's cheek cell:
4x--100 mm/or
10x--60 mm/or
40x--59.8 mm/or
Algea 1
4x--650 mm/or
10x--600 mm/or
40x--26 mm/or (26 was the measurable unit because it extended beyond the measurement capacity of the ruler)
Description: Long, rectangular, green
Algea 2
4x--104 mm/or
10x--150 mm/or
40x--130 mm/or
Description: Small, brownish
Buttercup Mature Root
4x--52 mm/or
10x--6 mm/or
40x--57.2 mm/or
Description: Small, circular
Flowering Plant
4x--104 mm/or
10x--100 mm/or
40x--130 mm/or
Description: Long, thin, rectangular
Conclusions:
Well, our observations have led us to believe that the size of the organism and the size of the cells are independent of each other. For example, we noticed that the buttercup mature root had almost the same size as that of a human cheek cell. We, therefore, cannot say with any certainty that this presumed relationship exists.
Hypothesis:
If two organisms (regardless of their size) belong to the same species, then their cell sizes will be similar.
Motivation of Hypothesis:
Common sense told us that all cells are not the same size. For example, an ostrich egg is one complete cell while an amoeba is also one complete cell but of significantly smaller size. But within the same species if size differs, then the quantity of cells may differ but the size of the cells which actually make up the organism does not differ.
Observations:
(Human)
5'7" --> 10x = 7 um/OR
5'5" ---> 10x = 7 um/OR
(Maple leaf)
4" --> 10x = 2 um/OR
1.5" --> 10x = 2 um/OR
(Clover leaf)
1/2" --> 10x = 1.5 um/OR
1/4" --> 10x = 1.5 um/OR
(Mushroom)
3/4" --> 10x = 3 um/OR
1/2" --> 10x = 3 um/OR
Conclusions:
From the small sample of organisms we investigated we have concluded that our hypothesis is correct; as long as the specimens are within the same species their cell sizes are the same. However, within our sample of organisms cell sizes proved to differ between species relevant to the organisms' size (i.e. Humans over 5' tall, 7 um; clover leaves smaller than 1", 1.5 um).
Our data-
Buttercup- measured at 40x, 23or= 53.8 um
Corn- measured at 40x, 22or= 51.2 um
Moss- measured at 10x, 15or = 150 um (length)
Larynx- measured at 40x, 50or = 130 um (length)
Human Cheek- measured at 40x, 30or = 78 um
Our observations lead us to the conclusion that size of an organism is not the deciding factor in cell size. We noticed also that while some of the plant samples (buttercup and corn) were close in cellular size, the moss was much larger. So we can also derive that similar species do not necessarily have similar cell size. A question we have from our observations is, is the complexity of the cellular make up of an organism a factor in similarity in cell size?
Hypothesis: There is no correlation between the size of the organism and the size of the cell.
Observations:
Spinal Cord - 13 um
Buttercup - 39 um
Shark Brain - 36.4 um
Enor's Cheek - 80 um
Algae - 169 um
Our observations support our hypothesis in the sense that cell size had no relation to the size of the organism (seeing as how a human is larger than a tiny piece of algae). Our measurements were based on what appeared to be the average cell size - we measured the longest points.
Hypothesis:
Cell size has no direct relation to the size of the organism. The size of the organism is determined by the number of cells that it is composed of.
Observations:
Human Cells:
Vena Cava: Average 85um
Cheek cells: Average 70um
Plants:
Buttercup Root Cells: Average 46um
Algae cells: Average 50um
Conclusion:
Our observations show that our intitial hypothesis is correct. A human organism is composed of cells of different sizes. If
cell size determined the size of the organism, the sizes of the human cells would have been the same. Moreover, a buttercup is bigger than an algae plant, but its cells are smaller. Therefore, there is no direct relationship between the cell size and the size of the organism. Rather, we can hypothesize that each organism is composed of different cells and that the cell size varies with the particular kind and function of each cell (for instance, see the discrepancy in the size of different human cells).
Hypothesis: Size of cell ought not have a direct correlation with the size of the orgmanism. Rather, the relation ought to lie in the amount of cells an organism has in accord with it's size.
Butter Cup: 12um at 40x
Moss: 7um at 40x
Cheek: 1um at 40x
Based on the latter observations we conclude that our hypothesis holds true for the experiment. As shown, the size of a cheek cell was many times smaller than that of a butter cup cell. As is clear, a human is many times larger than a butter cup plant which goes to show that size of cell and size of organism are not directly correlated.
Cheek Cells
-cell 1- 5 um
-cell 2- 4 um
Note: In the animal/ human cells it was more difficult to measure, because the walls were globulous and not really as thick, or as perceptible as plant cell walls. All data has been converted.
Tonsil
-cell 1- 2.6 um
-cell 2- 4.6 um
Shark Brains
-cell 1- 13 um
-cell 2- 39 um
Human Skeletal Muscle
-cell 1- 22 um
-cell 2- 40 um
Spinal Cord
-cell 1- width 15 um, length 40 um
-cell 2- width 25 um, length 30 um
-cell 3- width 20 um, length 20 um
Alison and I agreed that our hypothesis was workable, but it still remains difficult to come upon an answer. The spinal cord is fairly large, and its cells were the largest, however, the shark brain cell was also comparable, as was cell 2 from the Human Skeletal Muscle. We have no conclusion other than that we believe that the size of cells has nothing to do with the size of the thing they make up. Since cells divide to make new cells, we really cannot make any sort of correlation between the sizes.
Hypothesis:
there is no correlation between cell size and organism size.
In order to prove we will look at cells from organisms of varying sizes. we will look at more than one cell from each organism in order to account for possible variation within the organism.
Observations:
1. Corn Cell: 70 um
2. Human Cheek Cell: 50 um
3. Elodia Cell: 100 um
We observed that there is no correlation between the size of an organism and the cell size of that organism.
Sub-hypotheses included: Cell shape will depend on presence/absence of a cell wall; cell size will depend on presence/absence of a cell wall; cell shape and size will depend on the function of the cell in the organism.
We based our hypotheses on previous observations collected in former biology classes.
We recorded the size measurements and shapes of cells from the bulbilis moss, earthworm cells and human nasal cells. Our data were:
Moss cells (In moss stem): long and thin, average 1,800 micrometers. Shape: rectangular.
Earthworm cells: average 100 micrometers. Shape: roughly oval or round.
Human nasal cells: average 650 micrometers. Shape: globby; roughly oval or round.
Our data and observations support our hypotheses, suggesting that larger organisms do not necessarily have larger cells (moss cells > human cells), and that cell size and shape does depend on absence or presence of a cell wall (the plant cells were decidedly larger, on average, and more rectangular or box-shaped than the animal cells).
We were not able to collect any data with regards to cell function; however , a new hypothesis would be that the cells in moss stems are long and thin because they are vascular cells, and that vascular cells are generally longer and thinner.
Hypothesis: We believe that cell size is irrelevant in relation to the size of an organisim.
Measurements:
Spinal Cord 14.0 um
Worm 36.4 um
Buttercup 44.2 um
Our findings suggest that the larger the organism, the smaller the cell size; however it is important to note the limited number of specimens that we measured (3). We are not confident in making any conclusion from our measurements. We feel we would need more specimens of different sizes to have a more inclusive summary of possible observations.
Hypothesis: Smaller organisms are made up of smaller cells and larger organisms are made of larger cells.
Observations:
Moss- 3 OR at 10x = 30 um for round cells
1 OR at 10x = 10 um for striped cells
Corn Prop root- 27 OR at 40x= 70.2 um
Human trachea- 7 OR at 40x= 18.2 um
Earthworm- 12 OR at 40 x = 31.2
Our collection of observations disproved our theory because the corn prop roots and the earthworm both had bigger cells than the trachea cells, although humans are larger organisms than earthworms. Also, corn prop roots had a significantly larger measurement of cells than humans even though they are around the same size.
So we concluded that the because the organism is large, that does not necessarily mean that the cells of that organisms are large and vica versa.
We assert that the size of a cell is NOT dependent upon the size of the entire organism.
MOTIVATION:
Although we HUMANS are large organisms in relationship to that of a plant, we are compoosed of extremely small cells. Each cellular size depends not upon the size of the organism but is POSSIBLY correlated to the function that cell executes in relationship to the larger body.
OBSERVATIONS:
WORM CELL 1430.0 um/OR @ LENS 4X
FLOWER CELL 91.0 um/OR @ LENS 40X
J'LONDON'S CHEEK CELL 500.0 um/OR @ LENS 100X
We find that our collected data supports the original hypothesis, in that the cheek cell of a 5'9.5" human being weighing an undisclosed amount proved to be the SMALLEST cell. While the worm, which is often times squished by the feet of human beings proved to have the LARGEST cell.
