How will more carbon dioxide affect the rate of photosynthesis?

How does an increased level of carbon dioxide affect a plant's growth rate?

• I'm doing a science project for my Earth Science 8A class: How does an increased level of carbon dioxide affect a plant's growth rate? How can i do this experiment? I only have a week to do this project. Any help is appreciated. Thanks

• Answer:

  Check with your local garden center: If they have young pea plants or radish or leaf lettuce seedlings you may be in luck - these are often available and grow fast so you can get something done in a week. Pick a nice window or other area with plenty of sunlight to carry out the experiment. You may need to move a table near the window. Get the largest wide mouth jars you can find, with tight-fitting lids, but a large enough opening to put the potted seedlings into. If the seedlings come in a tray, get a whole tray and separate the tray cups with scissors. Try to match them up in pairs, with each member of the pair being about the same size or height. One member of each pair will be your normal treatment (control), the other will go into a jar that you can set up to have higher carbon dioxide (test). You should probably set up a least 5 of each type, as follows: Control jars: Soak the seedling with water and gently place it into the jar. Use 1 plant per jar. Carefully measure the length of the plant from the soil to the end of its longest stem and leaf. Keep track of these measurements for the plants. Put the cap on. Leave it on, taking it off only 1 time each morning for 1 minute. Each jar should be labeled, CONTROL-1 through CONTROL-5. Use these labels to record your initial size measurements. Treatment jars: Do the same as above, but change the lids a little bit so you can get more carbon dioxide in. Because we breathe out more carbon dioxide than is found in normal atmospheric air, our breath is higher in carbon dioxide than normal air. So, make two small holes in the lids for each of the Treatment jars (about the size of a pencil). Get some sticky-tack to seal the holes after you have made them. Lable the Treatment jars TREATMENT 1 through TREATMENT 5. Use these labels to record your initial size measurements. Now, each morning when you take the lids off of the jars of the Control group for 1 minute, take the sticky tack off the holes of the other jars, and one at a time, insert a straw to the bottom of the jar. Exhale several times (probably three deep breaths will do it) and then quickly cover both holes in the lid, sealing in the carbon dioxide-rich air. Do this every day, in the morning. Give the Control jars a minute or so without lids, then put the lids back on. Give the Treatment jars new carbon-dioxide-rich breath, and make sure the lid holes are plugged as soon as you can after giving them new breaths. Anytime they seem to need more water (which is not likely within a week) you can just give them all the same amount, and make a note of how much. Try to set them up in the window so that each group, treatment and control, get the same amount of sunlight. If you can do that, then try to rotate them and switch places every day, so they all get the same amount of sun. After your week is up (or however long you have) you can take off all the lids. Measure the plants again, exactly the same way you did before. Once you have measured the plants, subtract the first measurement of the plant (before the experiment) from the second measurement (after the experiment). The difference between those measurements will be how much the plant has grown. See exactly how much each control plant has grown, and how much each treatment plant has grown. Average the change in growth for each group, and see if those are different. If they are extremely different between the 2 groups, its pretty easy to make a decision about whether the carbon dioxide made a difference. If it is not obvious, then think about which single plant grew the most, and which grew the least. You can discuss the results in all sorts of ways, and you can even use a paired T-test (a statistical test to compare averages) if you want. It is pretty easy to find out how to do one of those online. Good luck