As you can imagine, cigarette smoke contains many impurities that are inhaled in great numbers directly into the lung. For this reason, the alveolar spaces of the smoker contain numerous scavenger cells (macrophages) that are filled with engulfed (phagocytized) particles of impurities and debris, as illustrated in Picture of scavenger cells in a smoker's alveolus Under the microscope, with this high magnification, you can actually see the black and brown engulfed particles in the alveolar scavenger cells. Indeed, smoker's lung may have so much of this particulate material that the lung looks gray-black to the naked eye. Most of the time, you don't need a microscope to tell if someone is or was a heavy smoker. A naked eye examination of a smoker's lung will usually reveal an enlarged gray-black lung with enlarged air spaces (the emphysema, as you saw in Figure 4 and will see again in Figure 8).
The conclusion gives the overall verdict of the argument. You can also restate the ideas that you have discussed in the body paragraphs so as to make your point valid. The conclusion should also aim at motivating the reader to do research in the future. The conclusion is related to the argumentative introduction as the topic as well as the thesis statement is restated in a more convincing manner. The conclusion also gives you a platform of illustrating your decision concerning the argument in the article and why you have settled on that particular decision. Try not to introduce new ideas as they will give the readers an ideology that the article is not comprehensive enough.