Counting Germinated Seeds – as a scientist would!

Now that you have exposed seeds to different temperature and moisture conditions, it is time to see if these have had any effect on the number of seeds breaking dormancy.

Counting Seeds

1 Create a data table like the ones below in which to record your results. Using a data table helps you organize your data and can help you later when you present the data to others. Create one table for each gradient.

TEMPERATURE

Position in temperature gradient	Number of Seeds Breaking Dormancy	% of Seeds breaking Dormancy
1
2
3
4
5
6
7
8
9
10

MOISTURE

Position in moisture Gradient	Number of Drops of Water	Number of Seeds Breaking Dormancy	% of Seeds breaking Dormancy
1	0
2	5
3	10
4	15
5	20
6	25
7	30
8	35
9	40
10	45

2 Remove and set aside the cover of the Petri dish you are going to count first. Make sure you record which dish you are opening!

3 Draw a few of the seeds, and/or look at them with a magnifying glass or microscope. Using tweezers, carefully turn the seeds and check for white cracks and the beginnings of sprouts. Be careful not to crush them! Germinating seeds are very delicate.

4 Count the number of seeds that have broken dormancy in each Petri dish. To make counting easier, sort the seeds in the dish, placing seeds that have broken dormancy on one side and seeds that have not broken dormancy on the other.

5 Check your numbers. Count the number of seeds that have not broken dormancy. If you have counted correctly, the two numbers should add to 20 (or to the total number of seeds in the dish). If they do not add to 20, then you have miscounted. Recount until you are confident of your numbers.

6 Record the number of seeds that have broken dormancy in the correct row and column of the data table. Make sure you record the total number of seeds in each dish— you will need this number to calculate the percentage of seeds breaking dormancy.

7 Place the correct cover back on the Petri dish and repeat until you have counted the seeds in all the dishes.

Calculating Percentages

Calculate the percentage of seeds that germinated in each dish. Record the percentages. An easy way is to divide the number of seeds that broke dormancy by the total number of seeds. Then multiply that result by 100 and round the final number. For example, if there are 18 seeds in a dish and 7 broke dormancy, then divide 7 by 18 and multiply by 100.

A short cut! As you used 20 seeds in each dish, and because 20 is 1/5 of 100, simply multiply the number of seeds that broke dormancy by 5 to get the percentage. If, say, 8 out of 20 seeds broke dormancy, then 8 * 5 = 40. Therefore, 40% of seeds broke dormancy. Now you can compare results from the two dishes!

Percentages in Science

In the long run: Why are percentages so important in mathematics and science? Percentages allow you to compare two values that otherwise could not easily be compared. For example, if one dish has 7 out of 18 seeds breaking dormancy, and another has 8 out of 20 seeds breaking dormancy, which dish would you say is more a more favorable environment for seed germination? By calculating percentages, you are calculating what the comparable number of seeds breaking dormancy would be if both dishes contained 100 seeds.

Working with Graphs

1 Graph the results. What sort of graph best represents your results? A bar graph? A pie chart? A line graph? If you were to use a bar graph or line graph, which value would you represent using the X-axis? Which one would you put on the Y-axis? Why? Should you put all of the results on one graph, or do a separate graph for each stack?

2 Analyze the graph. Do any values look wrong or out of place? How much variation is there in the percentages at any one position? Does this concern you? Do you see any patterns? How would you describe the shape of the graph? Does temperature appear to affect breaking dormancy? Does water appear to affect breaking dormancy?

3 Average the percentages across gradients. Averages allow you to group (or aggregate) data across many samples that are similar. The more samples you have taken into account, the more confidant you can be of the result. For example, three values for position four in the stack is more representative of what is really happening there than one value for that position. To average the percentages across the gradient stacks, add the percentages for each position together and divide by the number of stacks.

4 Graph the averages. Think again about the best way to represent the percentage data. Do you want to use the same type of graph you used in Step 1? Do you want to add these values to your graph from Step 1?

5 Analyze the graph. How do the averages look compared with the individual percentages? Can you see an advantage of averaging results? Does temperature appear to affect breaking dormancy? Does water appear to affect breaking dormancy?