plants

[lil jo]

Do plants have a circadian rythm?? I want to see if there is a difference between the growth of a seed/plant that gets 12 hours of light during the day and another one getting 12 hours of light during the night. I am also going to grow another seed with no light and one with 24 hours of light. I think I am going to use radish seeds. Do you think radish seeds will be good for this experiment??? I am hoping to see some differences between the two plants getting 12 hours of light. We looked on the internet but we could not find anything that addresses this issue. I am in fourth grade.

Thanks,lil jo

[HeatherL]

Hi Lil Jo,

What an interesting question! Yes, plants have a sort of circadian rhythm, as they respond to different "photoperiods." Different plants respond differently, but I did a quick search on Google Scholar, and it looks like radish plants will work well for your experiment. (I am an animal biologist and don't know a lot about different plants, though, so maybe a botanist can follow up on this for me.)

Here is a link to an abstract about a photoperiod study using radishes: http://www.blackwell-synergy.com/doi/ab ... alCode=ppl
Don't worry too much about the scientific words. The point is to show that radishes do respond to changes in photoperiod.

I think your experiment sounds good. You have four experimental groups to compare: [1] 12 hours light (day) / 12 hours dark (night), [2] 12 hours light (at night), 12 hours dark (during day), [3] 24 hours light, and [4] 24 hours dark. A few things to consider:
(1) What is the natural light cycle where you live right now?
(2) What is the typical light cycle under which radishes grow?
(3) Will the plants react differently if they are all grown under a common light cycle, and then changed to your four experimental groups?

Keep in mind that I think your experiment is fine as you have designed it. Your independent variable is the light cycle or photoperiod. Now it's time to think about your dependent variable(s) - the things you will measure to see if there are differences. Are you looking for time of germination, growth rate, or other responses (e.g., number of leaves)? You can look for any or all of these things, and see what variables are different and what may be the same.

Best of luck, and feel free to post with more questions!
Heather

[lil jo]

Heather,
Thank you for responding. We are in Missouri with short winter days. I'm not sure what the natural life cycle is for a radish but we will need to find out. I'm not sure what you mean by your third question. What kind of difference would it mke if they are grown under a common light and then changed versus just doing with the different lights??
We will probably measure germination time, roots, stem length, leaf number. Any other suggestions??
THanks

[HeatherL]

I'm not sure what you mean by your third question. What kind of difference would it mke if they are grown under a common light and then changed versus just doing with the different lights?? We will probably measure germination time, roots, stem length, leaf number. Any other suggestions??

Let me explain my third question better. Since your main question was whether your two 12-hour treatments would show a difference, I was thinking about whether you would raise seeds in the treatments prior to germination. My thought is that, to the plant that has not experienced a photoperiod before (inside the seed), the two 12-hour treatments would seem identical, since the plant has no previous reference of "night" versus "day." If, in contrast, you allowed the seeds to germinate in a common photoperiod and then changed that period, you might be more likely to see effects of different treatments, because the plant began with a reference. That would also allow you to have a "control" group, in which the reference photoperiod is not changed.

If you do decide to let the plants germinate in a common light cycle, then germination time won't be one of your dependent variables. Your other measurements are great, though.

In the end, my third question leads to a slightly different experiment than what you originally proposed. It may be that seeds do have an inherent circadian rhythm, in which case you can raise them in the treatments from the start. Just make sure that all your other conditions are the same: amount of soil available, amount of water given, how direct your light is, etc.

If you're really keen, you can do both experiments: one in which the seedlings start in a common photoperiod, and one in which the seeds germinate in the different light treatments. This will actually get at the question of whether there is an inborn circadian rhythm (i.e., in the genes), or whether the rhythm is developed by the plant's early experiences.

Either way you go, it sounds like you're on the right track. I hope I didn't confuse you!

Good luck, and please keep me posted about your progress!
Heather

[lil jo]

what would my hypothesis be?? what is the control group??
Thanks, lil jo

[HeatherL]

Hi Lil Jo,

what would my hypothesis be?? what is the control group??

Your control group will depend on which experiment you choose to do. Let's think about it for each situation.

(1) Germinate the seeds in different light treatments
Technically, the control for this would be "normal," or what you can expect the plants to experience normally. You can make this what your research says is the typical light cycle for radish plants, or you can duplicate the light cycle that you currently experience where you live. You just need to justify the reasons for considering this group your "control."

(2) Germinate the seeds in the same treatment, then impose different photoperiods.
In this experiment, the control group would be plants for which you do NOT change the photoperiod from the one in which they germinated.

Now let's think about your hypotheses. Based on the measurements you plan to take, you will have four hypotheses.

We will probably measure germination time, roots, stem length, leaf number.

You will come up with a hypothesis for each of your measurements. These are predictions that you should base on your background research.
[1] How do you think photoperiod will affect germination time? (This only applies to the first version of the experiment.)
(a) Do you think longer light periods per day will speed up germination (reduce the time it takes)?
(b) Do you think your two 12-hour treatments will have different times to germination?
[2] How do you think photoperiod will affect the roots?
(a) number of roots
(b) size of roots
[3] How do you think photoperiod will affect stem length? You can relate this to growth rate.
[4] How do you think photoperiod will affect leaf number?

Again, your predictions should be based on your background research, so I can't really make those predictions for you. However, the cool thing about science is that it's okay - and often just as interesting - if your results don't match your original predictions!

Let me know what you find out, and what your predictions are!

Cheers,
Heather

[lil jo]

Does anyone know the typical light cycle for a radish plant??? We need this to determine how long to expose the plant to light: 12 hours, 14 hours...
Thank You

[HeatherL]

Hi Lil Jo,

I found a very informative article, which says that radishes have no specific photoperiod requirement! This article also talks about the seeds responding to their environment prior to germination, particularly if they are located 1cm below the surface. I think this article will help you a lot:
http://www.regional.org.au/au/asa/1998/6/164murphy.htm
(You should also follow up on some of the articles that this one cites, if possible.)

I also found a study that used a 16h/8h light/dark cycle for their experiments: http://www.sciencedirect.com/science?_o ... 0a964373f7
The authors don't say why they picked that light cycle, but you can cite this study as a reason for picking yours.

The bottom line is that it looks like you can pick whatever photoperiods interest you most, and that your original plan of starting prior to germination seems like a good one!

Hope that helps.

Heather

[lil jo]

Boy, this is getting complicating. I don't think I can control the amount of water they all get because I think that the plants getting 24 hours of light will need more water than the plants getting no light. I had planned on giving all the plants the same amount of water during the expewriment. I also think I can't test for germination because they are under soil and they could be at different depths so I won't know when they start to sprout. What do you think?? I was going to look at stem length, leaf growth, root growth, end weight, and germination time. Can I do all this with the seeds already under soil?
Thanks
lil jo

[Grace]

Hi Lil Jo,

WATER:

Since your experiment is testing the effects of photoperiod, it would be best if you only changed conditions related to photoperiod. This means that you need to give all of your plants the same amount of water (keep water as a controlled variable). The reason why you should not have varying amounts of water is because water's effect on growth is *not* your primary question.

For example, if you found that X hours of light caused less root growth than Y hours of light, the only way that you would know the difference in root growth is due to the photoperiod is if all other conditions were kept the same between the two groups. If you changed photoperiod as well as watering, then you cannot tell if the different effects are due to light or water. However, the final decision is up to you because it is your project.

GERMINATION & ROOT GROWTH:

You are right; testing germination and root growth will be hard if your plants are buried in the soil (as they should be). However, there is an alternate way for you to observe germination! See the following links for instructions on how to germinate seeds in a ziploc bag, which would allow you to see germination - I think that it would help your experiment a lot!

http://askabiologist.asu.edu/expstuff/e ... ivity.html
http://www.greendealer-exotic-seeds.com ... ckBag.html
http://www.kidzone.ws/science/seeds.htm

You could put your seeds in a ziploc bag (one seed per bag) with a wet paper towel. The paper towel would provide needed water and at the same time allow you to easily determine when the plant is germinating. I have tried this with beans and other seeds, but I have not tried it with radishes in particular. If you have time, you could test if a radish seed will germinate in this way - just put one or two seeds in a ziploc bag, tape it onto a window with direct sunlight during the daytime, and observe whether it germinates. If it does, then you could use this in your experiment.

After the seeds germinate in the bag, you can then transfer them to soil for the rest of the experiment. Another possibility is to leave the plant in the bag for the entire experiment and just add water to the bag at regular intervals.

Hope this helps. Remember to have fun with your project!!

Grace

[HeatherL]

Hi Lil Jo,

I don't think I can control the amount of water they all get because I think that the plants getting 24 hours of light will need more water than the plants getting no light.

What caused you to make this prediction? It may be that plants under 24 hours of light need more water, but that kind of finding would be part of the results of the experiment! You most definitely should give your plants the same amount of water, regardless of the treatment. Remember that, to do an experiment properly, you need to control all conditions EXCEPT your independent variable (the thing you're changing). Your independent variable is light cycle; all other conditions need to be the same.

Think about it for a moment. If you saw greater growth rate in your 24-hour plants but gave them more water, you wouldn't know whether it's because of the light or because you gave them more water!

I also think I can't test for germination because they are under soil and they could be at different depths so I won't know when they start to sprout. What do you think?? I was going to look at stem length, leaf growth, root growth, end weight, and germination time. Can I do all this with the seeds already under soil?

If you have already planted your seeds, and you're not sure of their depth in the soil, then you can't say much about germination time. If you wanted to look at germination time, you needed to plant the seeds at the same depth. (This gets back to the "control" thing again.) That said, your other variables are good ones, and you still have a really cool experiment.

Good luck, and keep posting if you need more help.

Cheers,
Heather

[lil jo]

well I did it !!!My results are interesting. The 24 hour plants did the best. They were the healthiest: had short thick stems that eventually turned into radishes! They had the largest leaves. They also took the longest to germinate, 5 days. Any thoughts on this? I had hypothesized that these wouldn't do as well because of too much light. I think the light intensity wasn't strong enough. The palnts left in the dark took the shortest to germinate, 4 days. The only thing I can think of is the water. The ones in the dark were the wettest because they got no light and the ones in the 24 hour light were the driest.
This did become an issue as we went along. We had to stop watering so much because the plants were all getting too wet except for the 24 hour light plants. We did water them all the same amount of water at the same time.

The two 12 hour plants didn't do as well. The stems grew longer and there was no radish. There were differences between the 2 groups but I don't know if it is enough to make a difference. The 12 hour day plants took 4.4 days to germinate and the 12 hour night plants took 4.6 days. The 12 day plants had 4.4 leaves and the 12 night had 3.8. The weight of the 12 day plants was .96 g and the 12 night was 1.05. Stem length was 3.4 for the 12 day plants and 3.62 for the 12 night plants.
The length of the first radish leaves was 6.35 for the 12 day group and 5.97 for the 12 night group. One cup in the 12 night group had really little leaves and if you take that one out the average comes to 7.2 for that group. We couldn't do anything with the root system because it was so fragile it tore off when we took the plants out of the soil.
Do you think these numbers show a difference??
Thanks.

[HeatherL]

Hi Lil Jo,

Congratulations on a job well done! You do have some very interesting results, and I'm very happy that you do!

I think that your observations about the water levels are very clever. It looks like you have an interaction between light levels and water levels, and that you need the perfect combination to produce healthy radishes. Good job! Definitely include those observations in your report.

I'm not sure of the level at which you are required to report your findings. If you would like to see if there is a statistically significant difference among your groups, there are some simple tests you can do in Excel. Can you tell me whether you need to or would like to do some statistics?

If statistics aren't necessary, I'd say that your findings are still interesting. Although your two 12-hour groups are close to one another, the differences you observed are still interesting to report. Try making simple graphs (like bar graphs) of your measurements among the groups, and see if the 12-hour groups show differences that are consistent with the differences you saw between the constant dark and constant night groups. In other words, did the 12 day plants fall closer to the constant dark plants, and the 12 night plants closer to the constant day plants, for all your measurements? Or was it a mix? In other words, you can see if there are trends that become obvious when you graph your intermediate groups between the two extremes.

Take another look at your data, and let me know how the trends look! Also, let me know if you'd like me to give you some simple statistics to help you decide if your numbers show a true difference.

Cheers,
Heather