Science Buddies: "Ask an Expert"

Hello:

My 13-year old daughter if working on a Phototropism project for her 7th Grade Science project. The project consists of 3 trials of 5 pint-sized cartons with 4 lima beans planted in each carton. Carton 1 grows in normal light, Carton 2 receives no light at all, Carton 3 has 1 small hole on the side, Carton 4 has 2 small holes and Carton 5 has 4 small holes. We are trying to measure the angle of the plants' growth toward the light and there does not appear to be a great deal of difference between the various cartons. Should the seedlings in the cartons with more holes be growing at a greater angle toward the light than the seedlings in cartons with less light? Also, should this angle be decreasing or increasing as time goes by?

Thank you for your assistance,

Eric Reimer

Hi Eric,

It surprises me that the plants in different light conditions look similar. There should be quite a difference (especially between the ones grown in normal light vs. the rest of them). Do the plants with no light look etiolated to you (that is, have they lost their chlorophyll...do they look white and sickly)? If not, it could be that light is seeping in somewhere and that's why they all look the same. I'm not sure of the procedure you have followed, but here is a link to a science buddies experiment. Perhaps you can compare it to yours (to see if there is a source of contamination or perhaps you haven't done the experiment long enough?). https://www.sciencebuddies.org/science- ... #procedure

I'm not entirely sure what the results would be of the experiment, whether those with more light would bend more...I imagine this probably has more to do with the location of the holes. Intuitively I would guess that those that only have one or two holes would bend at a greater angle to get to the light than those that don't have to "work" so hard to get sunlight. But, that is just my hypothesis...it could be incorrect...but that's part of the fun of doing the experiment...sometimes things work out differently than you would expect.

I hope this was helpful. I also found a nice website that talks about phototropism and has some good pictures of plants that have undergone similar experiments (though not quite as extensive...they used fewer variables).

http://www.scienceclarified.com/Oi-Ph/P ... ism.html#b

Alexis

Thank you Alexis. Your response was very helpful. And yes, you are correct, the plants with minimal or no light look very sickly and are "pale". IT does appear that the angle is greater on those plants with only one or two holes. Would you expect that the angle would remain consistent as the plants grow or should they start to straighten as they receive the various amount of light.

Thanks very much for the links as well,

Eric