Science Buddies: "Ask an Expert"

Hi,
I am planning on doing the experiment: Too Much of a Good Thing? The Effect of Fertilizers on Algal Growth. For the experiment, it says that data can be measured by creating a scale from 1-5 to represent algae growth. However, I would like a more quantitative method of obtaining the results. The Make It Your Own Section states that the method in the Moss is Boss experiment can be used, but I'm not sure how to use this method. Do you transfer the algae-filled water to a square container and measure the area? How would you measure the area that it takes up and how big would the squares be? Is that process accurate (counting the number of squares) or is it prone to errors? I really don't want to use any expensive equipment, so it'd be great if someone could explain this to me ASAP.

Thank you!

- Sanjana R.

Hi,

Sorry that no one has gotten back to you about your question. I am not familiar with the method you describe but if it worked for the other project, just follow their directions.

My take on how to quantitate the algae growth would be to photograph the algae cultures under the exact same lighting conditions and use the ImageJ program to determine the image density. The greater the algal growth, the darker green it will be and the denser the image.

ImageJ is a free online program that scientists use for quantitatively measuring image density. When you use the program you will get a numerical value that you can use to compare one sample to another to allow you to say which one has the greater growth and by how much.

Here's the download for ImageJ:

https://imagej.net/Downloads

If you have more questions, let me know.

Sybee

Hi Sybee,

Thank you so much for the help! I have downloaded the ImageJ software, but I am not sure which category to look at to measure the algae growth. Do you suggest that I use the count, total area, average size, or % area to quantify the growth? Also, what do the total area and % area represent and are the area and average size in a specific unit of measurement?

Once again, thank you so much!

Sanjana R.

Hi Sanjana,

It doesn't really matter which measurement mode you choose as long as you use the same one for each image. You will get a value that correlates with the intensity, but there is no actual unit. When I measure image intensity I drag an area that covers the main part of the band that I am measuring and then place this rectangular area around each image in turn. The program gives you a pixel value for the area so you can directly compare all your intensity readings.

I hope that makes sense. It would be a lot easier if I could show you how to do it, but there are Youtube videos that are pretty good tutorials on ImageJ.

Post again if you have more questions.

Sybee