to get the energy they need, when plants are in seeds, they feed off of the oil within the seed, when they are out of the seed, they need more than one way to gain energy like photosynthesis

Actually it’s about the chemical properties of the chlorophile molecule. Because other pigments can use other types of light too. For example, bacteriochlorophil can use infrared light…

plants like to absorb red and purple lights relatively but dislike green so they are green…

I hate plants, but I remember that there is something called ChI moleculde in something called reaction center inside the chlorophyll that only absorb wavelength of 690nm, and pass the electron to a electron transport chain to generate ATP.

Why 680? it has to do with electron excited to different orbits and energy difference between two oribts is exactly given by 680nv x h

I hope I confuse you more! hehe

We’ll probably need a biophysicist to figure it out, probably this has to do with the mount of energy needed to photolyse water or maybe other efficiency issues

actually, what blackmangoes is referring to is the chlorophil a molecule in the center of each photosystem. for photosystem I it is 700nm(that’s why the molecule is named P700) and for photosystem II it is 680nm
I have no idea why they are like this though, probably some physics stuff…