What influences the overall growth pattern in a country? why is population growth a concern in society?

I know I cannot be extremely helpful on this, but I do know a good amount about answering the second part of your question. Population growth can be a concern in a society because, for example: 
If a great amount of people suddenly locate in a certain society, the economy could start to go down because there are more people to feed and not enough supplies. This can then cause higher taxes which can cause more poverty and so on. Like a domino effect.