Just like a food chain, energy enters the food web at the trophic level of the producers, which can also be called autotrophs. In the desert, autotrophs are often some type of cactus, grass, or shrub.
The main purpose of the INTRODUCTION is to give a description of the problem that will be addressed. In this section the researcher might discuss the nature of the research, the purpose of the research, the significance of the research problem, and the research question(s) to be addressed. Three essential parts of a good introduction are: RATIONALE.
From this attention grabbing opener, you would need to move to the next part of the introduction, in which you offer some relevant background on the specific purpose of the essay. This section helps the reader see why you are focusing on this topic and makes the transition to the main point of your paper.