Science Buddies: "Ask an Expert"

I am currently trying to conduct an experiment that involves plants, light, and gasses. I thought that I would expose the plants to different surroundings (the gas and the light) for the same amount of time each day for a couple of weeks. I am hoping that there will be some noticable difference when the time-span is over.

I need to know what kind of container would be ideal for keeping the gasses contained (I was thinking to use either Co2 &/or Helium) while still keeping the plants alive.

I was also wondering what an ideal exposure time would be for the plants. I don't want to underexpose them so that nothing will happen, but I don't want to quickly kill the plants.

This project is due on the 5th of January. Any help would be great.

It should be possible to keep plants in a mostly closed jar or plastic bottle or aquarium for a few weeks, as long as they are not too hot. If they get too hot, they may wilt even if the jar has plenty of moisture in it.

With pure CO2, the plants ought to be able to survive indefinitely, since they can make their own oxygen...as long as they have room to grow. Helium is much more problematic because you are essentially preventing the plant from breathing. I don't know how long it would take for a plant to die in that sort of environment, but plants are pretty hardy. I would thus suggest erring on the side of more exposure rather than less, especially since you only have a few weeks--something like half the day or during the day when you're in school or something. Keep in mind that you may get very different results if you expose them at night rather than during the day when they are actively photosynthesizing!