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Name: Victoria
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I'm doing a science project and I was going to do it on on much carbon dioxide a plant makes. What type of plant should I use? Will I be able to find a co2 gauge that is small enough?

NOTE: Dr. Ross' response is based on the assumption that you wanted to measure oxygen release rather than carbon dioxide. Measuring oxygen does make much more sense in trying to measure photosynthetic activity. ---------------------------------------

This is a fairly long answer, but it mainly will tell you web sites to look at, maybe with help from your teacher. As you think about the answers people give you, you might want to ask other questions. You might be asking this question because you want to know about global - Show quoted text - climate change, or about crops and food, or even how long people can live in a space station, if they have plants too. But we'll try to answer your question as it was asked.

You could watch a plant called/ Elodea/, an aquatic plant, take CO2 out of the water (bicarbonate in solution), which you don't "see" by watching it produce O2 (gas) bubbles that you DO see. Do it with and without a bright light on the plant.

OR, some school demos measure photosynthesis indirectly, by masking part of a leaf so it doesn't get light (chlorophyll disappears in that part), and measuring starch produced (or not produced, if it's under the foil mask).

*here are some web sites on photosynthesis*

_ very cute little Flash from Nova / PBS

Simplified version from the Public TV Show, Newton's apple- " Photosynthesis"
The "Teachers Guide" has an "Activity" that could be used to develop an Experiment- leaves from different species, OR foil left on for different amounts of time, OR foil masks on plants growing at different light levels (or plants growing in different environmental conditions in general, as long as the light/water/nutrients/toxins were not so limiting/toxic as to kill the plant).

Cartoonish but accurate from "Flying Turtle"

There is a PBS show, "Middle School Biology- Exploring Photosynthesis". It's scheduled on August 30th (in Iowa) :
"It reveals the chemical processes of both respiration and photosynthesis and the products that are produced. An experiment with a variegated leaf demonstrates that photosynthesis takes place in the green cells of leaves. " I don't know when or if it will be scheduled on other PBS stations.

_ (Long, text-filled; has a section, "Why study photosynthesis?")

_ a cool way to measure O2 evolution in leaf disks, by time-to-float. Very British (sodium hydrogen carbonate is sodium bicarbonate, aka baking soda, if you're at home); go down the page to "*STUDENT ACTIVITY GUIDE*" for explanation and pictures before reading the rest! It's designed as a species comparison (shade tolerant species vs high-light requiring species, and white light vs. green light, but could be adapted to compare plants grown in different conditions, or providing different amounts of light to the disks in the syringes.

_ (an/ Elodea/ experiment. Uses pH of solutions to determine differences in CO2 depletion. Variable is light intensity- she might think of others, but it is a short-term experiment)

Another/ Elodea/ experiment - counts O2 bubbles

(1-/ Elodea/ photosynthesis and respiration, uses pH meter, could substitute pH paper; 2-pigment separation, no solvent specified)

_ This has some
really cool ideas, but some uncommon (and some nasty) chemicals; does indicate some ways to simplify. One could choose one of the methods, and, if it works well at home/school, use it to explore various questions about plant pigments in relation to photosynthesis or species differences.


more pigment separation- and only uses rubbing alcohol, not lighter fluid!

_ _ Photosynthesis measured by starch production. Impacts of light/dark and of CO2 concentration in air (CO2 in air of one flask removed by absorption in potassium hydroxide solution.) Very cool website, mouse-over at bottom. Also British: / Industrial Methylated Spirit/ is denatured ethanol. Not sure why the caution about not using pure ethanol. Maybe it's too flammable. To extract chlorophyll (and measure it by spectrophotometry) we use cold 80% ethanol (in H20), but it takes 2 days in the dark to get it out. Hot (or warm) is faster. Quite possible that rubbing alcohol (70% isopropanol, I think) would work.

_ _

("Starch pictures"- advanced version of above. Could make the "picture" in reverse, by masking part of the leaf, and putting it in high light for the experiment. Sounds a little tricky/messy for setting up at home; requires hot alcohol and iodine. Lugol's solution (???) in supplies list never used in procedure.)

Steve Ross

Your teacher needs to give you some help on your project because you have a basic problem:
Plants consume CO2. In general they do not make CO2. Even when you resolve that understanding, actually measuring the level of CO2 in the enclosed container you will have to use could be tricky. Search the web for sites similar to what you propose to do and see how other people in the past have dealt with, for the objective of your project.

Vince Calder

Cellular respiration functioning in plants is dwarfed by animals, so carbon dioxide production is minimal at best. Photosynthesis would tend to use up any CO2 produced so measuring any release into the environment will be next to nothing, except maybe a very small amount at night with some plants. As a former junior high teacher, I can not recommend this project.

Steve Sample

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