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.
A final note: In constructing an introduction, make sure the introduction clearly reflects the goal or purpose of the assignment and that the thesis presents not only the topic to be discussed but also states a clear position about that topic that you will support and develop throughout the paper.