No idea about the scientific reasoning, but the leaves of the plant are where the most photosynthesizing has to happen. In order for the plant to get energy it has to absorb the most light. So it creates broad leaves. The reason they are green is because chloroplasts are green. I believe that the cells in the leaves have more chloroplasts so that they can catch more sunlight.<span />
The first invertebrates to show both segmentation and a complete digestive system belong to the phylum Annelida that includes earthworms, leech, sandworms, etc.
These segmented worms have complete digestive system which is also known as tube-within a tube. These can be found in freshwater, marine water or can even be terrestrial.
A molecule is non-polar if the charge distribution is symmetric and it is polar if the charge distribution is not symmetric.
The information collected from observations by scientists is primary data