Some more thoughts on cohesion!
Cohesion is one of the most important qualities in academic writing but it is one of the hardest things to describe and explain to students many of whom try to achieve it by simply adding lots of connecting words. But this is not necessarily a good strategy because this may make the text read awkwardly. Connecting words are important for cohesion but they are not the whole story.
When I look at the text above I see that there is cohesion - the text hangs together nicely and the ideas are linked well - but it isn't because there are a lot of words such as firstly, therefore and finally. In this short text the cohesion lies in the idea being introduced, and then further refined and discussed. When the idea appears again it is often referred to as it or this.
I hope the use of colours help you see how the ideas reappear - unfortunately it wasn't my idea but one I nicked from one of my favourite bloggers Dominic Cole. Read Dominic's excellent comments on cohesion here on his IELTS site.