Science Buddies: "Ask an Expert"

Hi,

I must design and perform an experiment for my school's science fair. I am interested in how free radicals affect cells and have decided that my experiment will measure the effect of free radicals on plant growth. I will do this by isolating wheat grass seeds inside a container filled with cotton balls, within a larger plastic enclosure. Next to the wheat grass will be hydrogen peroxide, placed with a catalyst, which will produce free radicals when they react together. The free radicals will then be able to be absorbed by the plant. I intend to compare how these radicals affect plant growth, by observing the growth of wheat grass under normal, natural conditions.

I am hoping to produce an amount of free radicals that will replicate the effects of free radicals from pollution, on a plant. However, I do not know how much hydrogen peroxide I will need and at what strength to do this effectively and produce distinct results. I am also unsure which catalyst will be the best to react with the hydrogen peroxide, so that I can produce a suitable amount of free radicals.

Any help would be greatly appreciated. Please ask questions if you are confused and I will do my best to elaborate (I know I have poorly explained!)

Thanks!

This article may be useful.

https://febs.onlinelibrary.wiley.com/do ... m%3Apubmed

It looks as if exposure to UV light may be a good and easy catalyst. As for how much Hydrogen Peroxide to use, I would advise using a few different amounts and reporting the differences in plant growth based on how much the plant is exposed to.

Thanks for the suggestions!
I just have a few more questions: due to the temperature that a reaction with a catalyst can reach, (and the threat this may pose for the plant) would the decomposition of hydrogen peroxide by itself with oxygen produce free radicals? I have seen other experiments just use the hydrogen peroxide by itself, but I am concerned that if it does produce free radicals without there being any catalyst or specific requirements (like the presence of metal ions which produce free radicals) the decomposition will take a long time. I only have two weeks!

How long do you think it would take to produce free radicals through this method with a low concentration?

Thanks

Also I am concerned about the heat produced due to a catalyst reaction, because i am enclosing the plant in a plastic structure to trap the free radicals produced so they are all absorbed. I don't want heat over 100 degrees Celsius being trapped in there!

Hello Tarag,

I don't see any evidence that the conversion of hydrogen peroxide (H2O2) to hydroxyl radicals and hydroperoxyl radicals by the Fenton reaction (https://en.wikipedia.org/wiki/Fenton%27s_reagent) generates enough heat to cause damage to plant tissues. In fact, the Fenton reagent (ferrous iron, Fe2+) has been used to treat human patients for certain conditions:

http://www.vivo.colostate.edu/hbooks/pa ... icals.html

The problem you have is deciding how much peroxide to use to expose your wheat sprouts to radicals--too much and you will kill all of them, too little and you won't see any effect. I have used 1% H2O2 to water the soil in potted plants to kill fungus gnat larvae and this did not visibly harm the plants.

The H2O2 you buy in the store is 3% so you could try it undiluted and diluted 1 to 3 and see if this has any effect on sprout growth, or whatever you planned to measure as your dependent variable. I don't know how much ferrous iron you will need to add as the catalyst, however, so this is something you will have to research online.

Don't think of radicals as necessarily bad. Your immune system has cells called neutrophils and macrophages that naturally produce hydroxyl radicals to kill pathogenic bacteria to protect you from infection. The body has very careful systems in place, however, to limit production of these highly toxic molecules and get rid of the excess quickly and safely.

Plants also have many ways to kill bad fungi and bacteria, but I don't know if they involve radicals. This is another subject you could research and report on as part of your project. It will make a very interesting story.

When you have more questions or need help with the experimental details, do let us know on this forum. We want your project to be a real success!

Sybee