Questions

Metropolis is a central city with the developed area surrounding it while Megalopolis is a region made up of 2 or more metropolitan areas.

Nominal money relates more to it's measure of counting - so nominal figure of what is written on bill, while "real" relates more to it's purchasing power (usually between some periods of time). For instance 100 units in nominal could buy 2 units of good in 1950 and 1 unit of good in 2005, at the same time real value of this 100 nominal units are 100 real units in 1950 and 50 real units in 2005.

Same is with GDP. In nominal it can rise due to inflation while it can stay the same or even decrease in real value.

Nucleus serves as the control center for cell metabolism and reproduction.

Herbivorous organisms are those that take for their food, plant parts like leaves raw in contrast to vegetarian, which means that plant products are taken raw or after being cooked.

A Jig saw puzzle pieces are in different colors which have different shapes. 

You can put it anywhere you like but there is only one right place for it to be fit in it.

Bookkeeper is the only English word that has three consecutive double letters.