What is the difference between microscopic and macroscopic ecosystems?

Microscopic approach considers the behaviour of every molecule by using statistical methods. In Macroscopic approach we are concerned with the gross or average effects of many molecules' infractions. 

Explanation:

Microscopic is the behaviour of every molecule using statistical methods. In Macroscopic approach we are concerned with theaverage effects of many molecules infractions. These effects, such as pressure and temperature,  can be measured with tools, or scientific instruments

the correct option is option a