Final answer:
Small cells are essential for increased surface area for nutrient absorption, efficient waste removal, and specialization of functions, which leads to efficient body functioning and survival of organisms.
Step-by-step explanation:
Trillions of small cells are crucial because they provide several critical advantages for the survival and functioning of organisms. One key reason is the increased surface area for nutrient absorption. This is demonstrated by the presence of villi and microvilli in the small intestine, which significantly boost nutrient uptake by diffusion. Another reason is the efficient waste removal. Due to the high surface area-to-volume ratio of smaller cells, waste products can be transported out of the cell more readily. Finally, there is the specialization for specific functions; complex organisms have cells that are specialized, making them more efficient at certain tasks and contributing to overall efficient control of body functions.