The Effect of UV Radiation on Lettuce Growth

[Challengedstudent]

Hi,
I'm doing a science fair project on the effect of radiation on lettuce growth and i have a question on the application of it. I'm not quite sure how it can help us in reality. Also, do any of you guys know a way to measure the changes of the lettuce growth (for ex: ways to see whether the lettuce is healthy or grown)

Please Answer as soon as possible.. Thank You

[Adean2001]

Hi,

I guess I am curious how you are going to conduct this experiment. Sunlight is the major source of UV radiation (which has a huge effect on plant growth). Are you going to somehow change the amount of sunlight each plant is receiving? There is a lot of practical application of this in relation to sunlight....especially for farmers/gardeners. If you could determine the optimal amount of sunlight necessary for lettuce growth, that could help us to understand where and when to plant lettuces. There are a lot of plants that thrive with little sunlight (and can grow in the shade and/or winter), whereas others need full sunlight and would die if you planted them in the shade.

In terms of measuring plant growth. I would take pictures of the plants at regular intervals...perhaps every three or four days. You can compare how they look. Their size, how "green" they are, etc. And then at the end of the experiment, I would take the entire lettuce plant and weigh it using a sensitive scale (if you have a balance available to you at school that would be best), or a kitchen scale would probably work nicely as well.

Good luck!
Alexis

[deleted-71536]

Hi Challengedstudent,

This is an interesting idea. How did you come up with it? What made you interested in the effects of radiation on plant growth? You can often find practical applications in your own reasons for deciding to do a project.

Many science projects have practical applications if you stop to think about it. A lot of our farming occurs in wide open spaces, and those farms can be near other facilities that require space, like nuclear testing facilities or even nuclear power plants. Because lettuce is a commercial crop, anything that affects its growth can also affect agriculture and the economy.

Here is some information about how you can measure plant growth: https://www.sciencebuddies.org/science- ... owth.shtml

I hope this helps. Please post again (in this same thread) if you have more questions.

Heather

[Challengedstudent]

Thank you for the tips,
So the way my experiment is going to work is that I'm going to plant about 6 lettuce seedlings. All of them will be exposed to a normal amount of sunlight (this way it is more applicable to people) and receive a normal amount of water. The only change will be the amount of UV Radiation I'm going to expose the plants to. For example, a batch of two plants will be exposed to an hour of radiation per day while another batch will be exposed to 2 hours per day. There will also be a control. By the end of a month, I'll observe the lettuce and see their characteristics to determine the effects of uv radiation on lettuce.

[Challengedstudent]

Thank you Heather, I'll definitely take your advice and ideas into consideration.

[SciB]

Hi,

Ultraviolet radiation at certain wavelengths and at a high intensity is dangerous to plants and animals. That’s why germicidal UV lamps for sterilizing areas carry a warning not to look at the light with unprotected eyes or expose your skin to it. What are you planning to use to irradiate the lettuce plants with UV? Why did you choose 1-2 hours as the duration for the dose?

UV damages the DNA, which over time—30 years or longer in humans--can lead to an accumulation of mutations and it is these DNA defects that are associated with cancer and aging. Unless you give your lettuce seedlings a very high dose of UV over the 1-2 hour period, there will probably be no measurable effects on its growth. You could see changes at a cellular level, but you would need access to a lab with advanced equipment to detect them.

I still think you should do the experiments, but depending on your UV source, you might want to also test a longer time, like 10 or 12 hours exposure—a whole day. Remember, people who are out in the sun a lot do not develop skin problems until many years later. UV radiation is much weaker in its biological effect than X-rays or gamma rays. If you do use a UV lamp remember to ALWAYS WEAR EYE PROTECTION, don’t expose your skin to the light and wear a face shield to protect your skin.

Please repost with any questions you have and we will help guide your project.

Best wishes,

Sybee

[Challengedstudent]

Hi, I am doing a project on the effects of uv radiation on lettuce growth. I get that radiation can slow the rate of photosynthesis and damage the cells of the plant, but can someone please help explain the exact science behind this and tell me other effects as well.
Thank You

[deleted-71603]

Hello. You have received excellent advice so far from our mentors. We noticed you posted this last question in a new thread. We have merged the two topics together to help our mentors answer your questions based on what has been done and discussed so far. Please keep all questions for your project in one threat.

Best of luck with your project!

[Challengedstudent]

Thank You Sybee for the advice and facts. I chose an exposure time of 1 and 2 hours because I felt that those exposure times would be the most realistic amounts as time goes on. As our ozone layer is gradually chipping down, we are getting exposed to more uv radiation. Eventually, the amount of uv radiation we get exposed to would probably be those amounts. But i think exposing the lettuce to 10 hours and 12 hours of uv radiation would be a better choice if i want to see any changes. If the judges ask me why i choice 10 and 12 hours though, what can i state that would apply to us, for i doubt in this time period at least, that there would ever be that much exposure of radiation to Earth. Also, I'm measuring my plants in the end using dry weight. So, if the lettuce weighs less, does that mean it is healthier, since most of the plant consisted of water?

Thank You

[deleted-71536]

Hi there,

I'm glad to see you are making progress with your project!

In terms of the exposure time, you can justify a whole day's exposure because lettuce is likely to be out in the sun for a full day. Also, you are trying to examine potential long-term effects in a short amount of time. That sometimes requires doing higher levels (or time periods) of exposure than you might expect to see normally. That allows you to get measurable effects more quickly, and that's how you could explain it to the judges. (Let me know if this does not make sense to you.)

A higher dry weight would indicate more growth of the plant. Although most of the plant is made up of water, the parts that actually grow are the structural elements of the plant. Dry weight measures the structural elements without the water, so a higher weight indicates more growth.

I hope that helps. Please let me know if you need more explanation or have more questions.

Heather

[Challengedstudent]

Thank You
So if the plant weighs more, that means it is healthier because it shows that the structures of the plant are properly growing compared to plants whose structures couldn't develop properly like those exposed to a high dose of radiation?

[deleted-71536]

Hi,

So if the plant weighs more, that means it is healthier because it shows that the structures of the plant are properly growing compared to plants whose structures couldn't develop properly like those exposed to a high dose of radiation?

Although you can't say this for sure, it is definitely one way to interpret those results. If the plant weighs more, you can absolutely say that it grew more. You cannot say for sure whether it was healthier, but it is likely that a healthy plant will be able to grow more than a plant that is not healthy.

Heather

[SciB]

Hi again,

The one question of mine that you still have not answered and which is really important is what is your source of UV? If you are trying to mimic a dose that would be a little higher than what we are getting now—say after the ozone layer decreases by half—then you will need a calibrated UV source and a UV dosimeter.

I need to know what the UV source is because 10 hours of UV radiation from some sources would kill the plants completely and that’s not the change you are looking for. Ideally the dose you give should be some percentage over the normal range so you can answer the question—what will happen to plant life if UV radiation levels increase by say 10% or 20%? But, in order to do that you need to know what the dose rate of your UV source is. Do you?

Can you please clarify how you planned to UV-irradiate your plants?

Sybee

[Challengedstudent]

oh I'm sorry sybee , I am using a fluorescent uvb bulb that can be attached to a terrarium (the ones that can be found in a pet store for lizards). Every evening, most likely starting five, I'm going to bring the plants in and put them in the terrarium. Then I'm going to UV radiate the first group of plants from 5 pm to 7 pm. After that, I'll take that group out and put the next group of plants in and radiate them for either 4 or 12 hours, depending on how much uvb could damage the plant. The UVB fluorescent bulb says that the uvb intensity for its size is 50 microwatts.

[SciB]

Hi,

As I understand your project, the hypothesis is that increased UV irradiation of plants will damage them, but of course if you give a high enough dose of UV you will kill all of them. As a science fair judge I would ask you what UV DOSE you plan to give the plants and how does that dose compare to the normal average daily UVB dose from the sun in your location and time of year?

Here’s where it gets technical. What I am calling the ‘dose’ of UV is the term we use in the lab when irradiating cells or tissues to refer to the TOTAL amount of energy that they are exposed to—an energy ‘dose’. This is not the same as the dose RATE. The technical term for the rate of energy transfer is ‘energy density’ and the units used to measure it are watts per second per square centimeter. What I call ‘dose’ would be the total amount of energy received and you would calculate that by multiplying the dose rate times the number of seconds that the plants were exposed to the light source.

The other important measurement is called ‘irradiance’ and it is the UV intensity in watts per square centimeter. The power of your aquarium lamp at UVB wavelengths you said was 50 microwatts (50 uW), but this does not mean that your lettuce plants will be getting 50 uW of UVB per second per square cm. The irradiance decreases as the square of the distance. The closer you get to the UV lamp, the stronger the irradiance. A plant that is right under the lamp will get more UV energy per second than one that is off at an angle to the end of the lamp. That’s why you really need a UV dosimeter to measure the UV intensity at various positions.

I am not trying to make your project too complicated, but when you are working with radiation you need to know the energy rate of your light sources in order to make any kind of valid conclusions. A UV dose given at a high intensity (irradiance) may have a greater effect on plant cells than the same dose at a lower rate. Conversely, if the dose rate or dose is too low, then you will see no effects. As I understand your question, you are asking what would happen to the lettuce plants if the UVB levels increased slightly over current levels—maybe double. So, you need to know two things: what is the current UVB irradiance from the sun at your location and what is the UVB irradiance of your light source?

I googled ways to measure UV intensity and found a company that sells UV-sensitive strips, but they are rather expensive: http://www.uvprocess.com/product.asp?code=INTS+LBL+B You could try calling them and ask for a donation of a few strips for educational purposes. Some companies are generous to students because they are the next generation of scientists. The other alternative would be to call around to whatever universities happen to be near you and ask if there are any researchers who might have a portable UV dosimeter that you could borrow for your measurements.

I hope this is helpful to you and we will be here to continue guiding you on your project.

Sybee

[Challengedstudent]

Thank you Sybee, as soon as I get the radiation strips I'll start measuring and calculating the radiation from both places. Do you think it is necessary to wear uv protective gloves when putting and removing the pots from the uv terrarium and if so, where can I find some. Thank you

[SciB]

Hi,

The only lamps that I have seen with a warning for skin protection are the 36" germicidal ones. Check with the manufacturer of your aquarium lamp to make find out what their recommendations are. Wear safety glasses to protect your eyes always.

Best wishes,

Sybee

[fabulousquantumpeewe]

Thats so nice how you help others, now could you help me and look at my thread that I need help on?! PLEASE! Its due in a week and I need to finish it!!

[deleted-71625]

Hello fabulousquantumpeewe,
Thanks for posting, I hope you had a nice holiday. I didn't see a particular question from you, did you post in another thread? It is best to ask your questions in the same thread, so we can all keep track of how your project is going. So, I am assuming you are doing the same project on UV radiation. Please tell me what you are working on and how we can help you. I know you have a week until it is due, so try to be as specific as you can about your project and your questions and we will help you the best we can. What do you have left to do? I look forward to hearing from you.

[Moderator note: This student had posted in the Getting Ready for the Science Fair forum. I have moved the topic to the Life Sciences forum, and you can view it here: https://www.sciencebuddies.org/science- ... 25&t=12721]

[Challengedstudent]

Thank You Sybee,
So I am unsure about how many watts/second/cm squared the plants receive from natural sunlight but i did manage to calculate the total amount of energy the plants will receive from the uv lamp (please correct me if I am wrong.) Given that the lamp radiates 50 microwatts (0.00005 watts i believe) and I am exposing the plant for 10 hours (36,000 seconds). So, the total energy or dose would be 1.8 watts. I know I still need the uv strips to measure the exact amount due to distance but this is just an estimate of the increase of radiation exposed. So, the question I am trying to ask is, would this approximate increase kill the plants. If so, should I reduce the time of exposure back to the initial times of 1 and 2 hours. Also, when I am using the uv strips to measure the amount of radiation, what time of day should I use it (when the sun is strongest probably). Thank You

[SciB]

Hi,

I agree that you will have to measure the actual UV dose for both the sun (at noon I would assume) and your lamp using the strips to get an actual intensity reading for comparing the two. Hopefully the test strips come with instructions on how to use them and what the readings mean. I would assume that your terrarium lamp does not produce anywhere near as high intensity as a germicidal lamp so i really don't know how long to expose the strips to get an accurate reading. I don't think you have to worry about killing the plants, though.

Are the strips sensitive enough to read the UV in sunlight? You might want to call the manufacturer and ask them if you can use their UV strips for the purposes you need.

Keep posting to this thread so we can keep answering your questions.

Good luck,

Sybee

[Challengedstudent]

Oh ok thank you Sybee. Even if there is no visible result from the uv radiated plants, when i use the measurement dry weight and weigh the plants, there should be some weight differences that could support my hypothesis right? So far, I've radiated the 2 groups of lettuce for 2 and 12 hours and there has been no visible change so I am just wondering.
Also, when I actually dry and weigh the lettuce to measure it, how am I suppose to do it. Do I weigh like 2 or 3 leaves from each group because each pot has a different amount of leaves. Please tell me the exact steps necessary for me to weigh the lettuce.
Please answer as soon as possible. Thanks

[SciB]

Hi,

Time is a big factor in the effects of radiation on organisms like plants and animals. Some effects, like after the Chernobyl nuclear power plant melt-down, did not show up for years. You would not see any changes in 12 hours unless you used a really high dose of UV and if you do that, then your experiment has no relevance to real life where the UV levels from sunlight are increasing only slightly as the ozone layer decreases.
Long-term irradiation of plants with slightly higher levels of UV could either inhibit or stimulate growth. We don't know. If you want to check the weight gain of your plants then you need to weigh the entire plant, minus the weight of the container plus dirt before the irradiation then weigh it again after two weeks or so. Subtracting the weight before UV from the weight afterwards and dividing by the weight before, times 100, will give you the percent change in weight. By comparing the percent change of the UV-irradiated plants to those receiving only normal light, you should be able to tell whether the irradiation affected growth rate.

The other thing you might be able to measure would be the effects of higher UV flux on chlorophyll in the leaves. I don't know this, but I am hypothesizing that UV can 'photo-bleach' the chlorophyll so that the leaf is paler than one from a plant in normal light. Check out these references: http://www.sciencedirect.com/science/ar ... 3205003521
http://www.ncbi.nlm.nih.gov/pubmed/18028201

To test photo-bleaching in the lab would require some pretty expensive equipment but I think you could get a rough measurement by carefully photographing a leaf from each plant under the same light conditions and the same distance and camera orientation, then comparing colors. There are some free image analysis programs online where you could actually quantitate the image density at a specific point. Try ImageJ http://rsbweb.nih.gov/ij/

If you have trouble figuring out how to use the program to measure image density, I can help you. The more quantitative readouts you can get for your experiment, the stronger your conclusions will be.

Hope this helps. Good luck!
Sybee

[Challengedstudent]

I will check out the chlorophyll test but for the weighing, I wanted to use dry weight to measure the plant growth. I read that I would need to heat up the leaves to take out all the water, thus putting it in the oven over night. So, in this case, do I take out a certain number of leaves to weigh and do I use a scale that goes down to milligrams? If this isn't viable for my project, please let me know and I'll stick with fresh weight for a measurement. My initial plan to support my hypothesis was to find the dry weights of all the lettuce groups and compare them. I was told that the higher the dry weight, the healthier the plant is. Please correct me if my information is wrong. Also, after 2 weeks, i noticed that the lettuce exposed to 12 hours of radiation seems to be the biggest and maybe the healthiest of the 3 groups of plants followed by the lettuce group exposed to 2 hours. May you please tell me whether this is a sign that the radiated plants are healthy or not or whether this even tells me anything. Based on this observation, I drew the conclusion that a low dose of uv radiation stimulates lettuce growth and that my hypothesis is wrong but i have very little information to support this. I have heard that plants developed adaptations to protect themselves from lots of uv radiation. They have protective mechanisms and i believe the minimum dose of radiation helped build up these mechanisms, but my science teacher says i need more information to present to the judges. May you please tell me what you think about this situation and why a low dose of radiation may support plant growth. If you have a website that you can link that'll be useful too. Thanks

[SciB]

Hi again,

You want the weight of the whole plant. Did you weigh the plants and container before you started the experiment? If not then your ending weights are not going to tell you much unless all the plants were nearly identical in weight at the start of the experiment. That’s why I had suggested weighing the plant and container first so that you could get the difference in weight expressed as a percentage later.
If you didn’t weigh the plants before irradiation then you will have to state this in your Methods section. Hopefully the plants were close in weight when you started. Yes you are correct that the greater the growth the greater the weight, but you can’t compare final weights unless you know the starting weight.

As to using fresh weight or dry weight—why not do both? Then you can compare them and see if the differences are the same. They should be. I really don’t see an advantage to drying them first, and drying might actually eliminate a difference in water content caused by irradiation. I have no reason to think that UV inhibits water uptake but then we don’t know, do we?

Use the best scale you can, preferably one with a sensitivity of tenths of a milligram.

I think your results are very interesting, but I have to ask you one thing—did all your plants get exactly the same total number of hours of light? Plants that get less light will grow slower than those getting more light. Remember that the UV lamp puts out light of other wavelengths as well as UV. Did the lamp come with a diagram that shows the spectral range of the light output—a plot of light intensity vs wavelength? If not, you should call the company and ask them to email this to you as you should have it for your presentation. Also, how close did you have the lamp to the leaves? Distance has a large effect on light intensity.

Plant adaptations to UV are usually genetic and take a long time, so I would not expect your lettuces to have produced their own SPF45 sunscreen so quickly. What about the color of the leaves? Is there any difference in the shade or intensity of the green? When chlorophyll is destroyed, the leaves become a paler green; conversely, if extra chlorophyll were being synthesized to handle extra light, then the leaves would appear darker green. UV at 348 nm would not be absorbed very much by chlorophyll a which has peaks at 430 and 660, but if the lamp produced a substantial amount of light in the violet/blue range, 400-450 nm then this light might stimulate photosynthesis. That's why you need the spectral response curve for the lamp. Check the Wiki on photosynthesis vs irradiance: http://en.wikipedia.org/wiki/PI_curve

Good luck!

Sybee

[Challengedstudent]

I was unaware that I had to weigh the plant before radiating it until just recently. I thought i would just weigh the leaves at the end of the project and that was the fresh weight (according to the information on plant measurement in science buddies) but if i fill an empty but same container with soil, can i just weigh that and say that was the weight of the pot + soil before the plants grew, for each container with soil should be quite the same. Is the method you explained a way to measure fresh weight? Also, i did some research about the effects of a low dose of uv radiation on plants and i found out some facts that could support my results currently.
First, there is the process of photomorphogenesis that may have caused the uv radiated plants to seem healthier. Photomorphogenesis is the development of plants by light and it is affected by different photoreceptors. Photomorphogenesis responds to UV Radiation (at the action spectrum 295-300 nm). This process affects the biosynthesis of particular flavonoid secondary metabolites. Flavonoids are pigments that perform certain functions such as uv-light protection. So, by stimulating biosynthesis of flavonoids, the plant would be more protected from radiation. As a result, i believe it could grow better without having the small affects of radiating hindering its growth. There's a certain photoreceptor though that really triggers photomorphogenesis, which is UVR8. UVR8 regulates the expression of genes that promotes survival in sunlight. I looked up what expression of genes is and i found out that expression of genes is the making of certain proteins. So, the UVR8 produces a protein Hy5 transcription factor which promotes photomorphogenesis. Finally, i found out that exposure to uv-b may reduce pest attacks on plants. I am unaware of the full affects but apparently, uv-b effects on plants were similar to the defense responses of plants when attacked by pest. For the weighing of the plants, may you please recommend a solution to my problem right now for I kind of depend on the weights for my results. Also, when i receive the uv-strips, i'm going to use them (i'll call the company to see how it works first) and then calculate the percentage of increase of radiation (I'm guessing that is the purpose of the strips) to support my project. I think using the uv strips will tell me the dose of radiating emitted from the certain distance. May you please take a look at my research and tell me if it is just enough to support my observation of the plants. If the looks are just deceiving and the weight justifies that the plants that aren't radiated are healthier (which i doubt would be the case) i still have a lot of research to back that up. Oh, also, I have read the link you sent me to "photo bleach" the leaves. From my understanding, i first take a picture of my 3 different types of leaves (all from the same distance and lighting) and then i can import them onto the imagejava app (for you need to download it). I haven't downloaded it for i wanted your consent first, but within the app, I've read that it, in a way, acts like a microscope and zooms in a little. Is that one of the features we are going to use or is there another feature in the website that you intended to use to measure or examine the chlorophyll.

Thank you very much!!

[SciB]

Wow, Tony! You sure did your homework on this one. My botany course was years ago and I was not aware of these findings about ‘photomorphogenesis’. That really makes your experiments more interesting because your original hypothesis, I think, was that UV would somehow inhibit growth of the lettuce. I think it may be a dose effect, however. UV at a certain intensity and time may stimulate growth while at a higher intensity and/or longer time, it will inhibit growth.

When you are comparing treated with control subjects whether plants or humans, you ALWAYS have to do a baseline reading BEFORE you start the treatment. How can you know the amount of change in weight if you don’t know the starting weight? Since you do not have starting weights for each plant, you will have to assume that the plants were identical in weight—which of course is not true, but hopefully they were ‘close’ in weight. Did you take photos of all the plants at the beginning of the experiment and then at various times along the way? Photos could be offered as evidence that the plants were all the same size to start with.

I would measure the fresh weight of the plants by carefully loosening the soil around the roots, pulling them out and brushing the soil off. You could dry them in an oven as you suggested, but I don’t see a reason to do this and as I said before, maybe water retention is a result of UV and you would not see that if you dried them.

The measurements of UV intensity are critical and you should have done those before you started the experiment to see just how much UV your lamp produced over the times that you used for exposure. You have to remember that the intensity of UV radiation decreases as the square of the distance from the source. I asked you before how you were going to place the UV lamp so your plants all received an equal intensity but I don’t think you ever answered me. To get an accurate measure of the intensity, you need to place the test strips at about the same distance from the lamp as the lettuce leaves were and leave them there for the same number of hours—unless the company has other instructions. If you have any questions, don’t hesitate to call technical support at the company that makes the strips. They will be very glad to answer your questions.

I’m not clear on what you did for the control plants vs the UV plants. Did you have the plants inside under artificial lighting or outside in the sun? Did you use the UV lamp in addition to the other light source? My conception of your experiment was that all the plants would get the same basic light whether sunlight or grow-lights but that the UV-treated plants would have the UV lamp on them for some number of hours a day in addition to their normal light. How did you do the experiment?

You have the right idea about how to measure the leaf color to determine if there were any changes in chlorophyll content in the leaves. And yes, you may download and use ImageJ—it is free. Here’s a link to some instructions for using ImageJ to measure leaf color: http://www.google.com/url?sa=t&rct=j&q= ... W0&cad=rja
There is a lot of information on the web about using ImageJ, but if you get stuck using the program, let me know and I will try and help you. Just be sure you take close-up pictures under exactly the same lighting and the same distance, and try to use leaves that are about the same size and maturity. You don’t want to compare a young fresh leaf to an old droopy one.

You have a lot to do in getting your data and be sure to record EVERYTHING in your lab notebook with the date. This is a great project and I’m looking forward to seeing what the weight and chlorophyll data can tell us about UV and its effect on plants. You may have found something that no one has seen before.

Good luck and keep posting!

Sybee

[Challengedstudent]

Thank you. I'll probably just measure the fresh weight then and also try finding a way to somewhat "match" the initial weight of the pot and soil in the beginning of my project. I actually bought a terrarium to hold my plants in and the uv lamp can just attach on top of it. So, everyday and all the plants will be exposed to the uv radiation at the same distance. Yes, for my project, i made sure all 3 groups of lettuce received the same conditions during the day and could grow properly. Nothing changed there. The only difference was that I radiated the lettuce for 2 and 12 hours each day while the control group didn't receive any radiation ( just to make sure all 3 groups of plants don't have different growing conditions I brought the control group indoors as well when I brought the other 2 lettuce groups in to radiate)
Thanks You for all your help, I'm doing my best with the research and by the end of my project, I'll measure both the fresh weight of one of the leaves and weigh the whole pot itself. I might try weighing the same type of pot filled with soil and say that was the initial weight even though it isn't that accurate. Due to the fact that I'm unfamiliar with the Image Analysis, I'll attempt to do it but most likely I'll need some help. I have read the instructions and I'm assuming that I might look for the dark green areas of the leaf as well to find the chlorophyll.

[SciB]

Hi,

I still have not completely understood how you treated the plants. Did you leave them in the sun all day and then bring them in at night to give the UV irradiation? If so, how many hours of sunlight did they receive per day? You said you brought the control plants in but did not give them UV. Were they in the dark?

If you gave the one group of plants 12 additional hours of light from the UV lamp then that may be why they grew more. The controls have to be identical to the experimental plants except for the addition of UV. You should have given the controls 2 or 12 hours more light WITHOUT UV.

As long as you explain this in your methods, then it is ok, but be careful with your conclusions as to cause and effect.

Sybee

[SciB]

Hi again,

If you are going to use growth as your measure of the effects of UV then you have to weigh the WHOLE plant--not just a leaf and not the soil. I explained to you how to do that.

I also asked you about photos.
Did you take photos of all the plants at the start of your experiment?
Did you take photos at different times during the experiment and at the end?
Did you take a photo of your terrarium with the lamp in place to show the set-up?

When you photograph the leaves to do the image analysis, be sure to do it as I said with the camera at the same distance from each leaf and the lighting EXACTLY the same. If you do not do this then your results will be useless. Also, be very careful to record which photo corresponds to which plant. It is all too easy to lose track of which is which and then everything is just a guess.

Science is really exciting, but you have to do experiments very carefully and logically or it doesn't work.

Please ask questions if you don't understand something. We're here to make your project the best it can be!

Sybee