1. The problem statement, all variables and given/known data Here is a question that I just came across while reading: Which of the following has the most primitive respiratory system? A. Rat B. Fish C. Toad D. Grasshopper E. Lizard I read thoroughly, with a view of having an answer to the question. Uptill now I have not made any success. Folks in the forum, please let's discuss it with a view of arriving at a correct answer. 2. Relevant equations No equation is involved. 3. The attempt at a solution The word primitive is used when one talks or make reference to something that has to do with acient period. Is use to refer to something that happened or done in early history of something. Now that the word (primitive) has come into this context. I don't know the type of respiratory system the first set of animal that elvoved used. I start by analyzing the respective ways each of the animal in question respire. The rat uses it's lung to respire. The fish uses it's gill for respiration in it habitat (water). The toad uses it's skin, mouth and lung to respire. The grasshopper respire by making use of it's spiracle under it (grasshopper) abodmen. The lizard uses it lung. From all my analysis, am choosing grasshopper as the animal that has the most primitive respiratory system based on the fact that it is the lowest in rank. What do I mean by lowest in rank? What I mean is this; all the animals mentioned are vertbrate while grasshopper is not. Does anyone have an idea about this?