That's a molecule of the substance. You can break the molecule down further, into the atoms that make it up, but those don't have the properties of the original 'compound'.
Here's an example:
-- Sodium is a soft, slippery metal, that explodes when water touches it.
-- Chlorine is a poisonous green gas.
When an atom of Sodium and an atom of Chlorine combine, they make one molecule of a substance called "Sodium Chloride". That's SALT ! It isn't green, it isn't a gas, it isn't poisonous, it isn't soft and slippery, and it doesn't explode when water touches it.
The said development of the cell where the three cell layers help out do it is called as Gastrulation. The three layers - called as ectoderm, endoderm, and mesoderm - tend to form as this happens. This is a process that's present in all living things except sponges.
Acceleration, a = (v - u)/t
where v is the final velocity, u is the initial velocity, and t is the time.
This formula on a velocity time graph represents the slope of the graph.