Science Buddies: "Ask an Expert"

conducted experiment regarding germinating seeds
group1-water added, no light; group 2- water and light added(light starts at day 4)
weighed (dry weight) at 7th and 14th days...
#1 7th day-1.79g, 14th day-1.25g (because it continues to essentially "eat itself" due to lack of photosynthesis???)
#2 day7-1.68g; day14-2.02g
(this is where I'm completely stumped....why does the water+light at day 4 group have a lower dry weight at day 7?)

<<<<<<Thank you for your time!!!:)>>>>>>>

Hi S,

This sounds like an interesting experiment.

Did you happen to weigh the seeds before starting the experiment? My guess is that the starting weight of the seeds varied. And, even ones that weighed the same may have varied in the amount of nutrition available for the plant. Germinating seeds also do not need sun when they first start to grow, so it may just be natural variation right from the start. If you have more time to do the experiment, you might consider germinating more seeds so you have more data to analyze (and if you don't, put that in your future study for your report).

The difference between the two is about 6% for day 7, and 60% for day 14 (from group 1 perspective). 6% isn't much compared to 60%!

Variations in temperature and other variables may also be a factor.

You did have a big difference at day 14 though, and that is the important part.

Good luck and let us know if you have more questions!

Conditions were kept the same.(except for independents)...initial dry weight was 1.96.....what would cause the dry weight of the seeds recieving light and water to be lower than those recieving just water (at day 7)? (it was a consistent result)....I am guessing it has something to do with the fact that water is broken down during photosynthesis (effectively lowering dry weight?)...but that does not sound right to me...prob something having to do with photosynthesis though...?

I'm not a plant expert, but I'm pretty sure that early in the germination process, the plant is not photosynthesizing--it usually doesn't start photosynthesis until the first leaves have pushed above the soil. However, plants must always respire (at least a little), and germinating plants are actively growing. This means that the seed needs to use up stored nutrients in order to grow, and those chemical reactions will give off heat, burning up some of the energy...and decreasing the mass of the seed.

Make sense?