<span>164.0
First we must look up the atomic weight of all elements in calcium nitrate
Ca: 40.078
N: 14.0067
O: 15.999
Then we compute the mass of the nitrate polyatomic ion which contains one nitrogen and 3 oxygen atoms.
14.0067+3*15.999 = 62.0037
For the entire molecule we calculate the weight of two nitrates and one calcium
2 * 62.0037 + 40.078 = 164.0152
rounding to the tenths place results in
164.0</span>
Well, I think it's mainly for photosynthesis and gas exchange. A leaf is normally flat, light, and thin, so that the sunlight can get to the chloroplasts in the cells.