5 Days of Fun Farm Science: Carbon Dioxide and Photosynthesis

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Photosynthesis is a big part of life here on our hobby farm. We have a huge garden, and a field full of corn (thanks to our neighbors' help). My kids understand pretty well about plants using the sun. We were talking recently about what plants take in and what they put out. Pretty simply out: a plant takes in the carbon dioxide in the air, and with water and energy from the sun transforms it to oxygen and glucose (plant sugar).

Through Supercharged Science we found the idea of this experiment to see if a plant in a closed space can add enough extra oxygen to keep a candle lit longer.

Materials we used:

• candle in a short base (and a way to light it)
• large glass jar
• pie pan of water
• stopwatch
• leafy plants of various sizes

The kids theorized (as did I) that the candle would stay lit slightly longer with the plant inside.

We did created a closed system by inverting the jar into a pan of water which the lit candle was setting in. We used a gallon jar and we repeated the entire progression of steps twice.

• With nothing in the jar the candle extinguished in 1.13 min. on our first try, and 1.01 min the second time. 
• With a small piece of kochia plant it extinguished in 55 seconds and 44 seconds on the second round.
• With a large plant of kochia (filling 1/4 of the jar) it took 53 seconds and 46 seconds.
• With a sunflower leaf (large) it took 45 seconds.

It seems the leaves displace more oxygen than they can replace in less than a minute, although the large kochia was slightly better. We also observed a cool effect of the vacuum pulling water up into the jar!

Even though our theory was disproved, we illustrated an important point in doing science experiments: minimizing variables.

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