Final answer:
Nutrient delivery systems in animals are tailored to their dietary needs, with structures like villi and microvilli in the small intestine of vertebrates and specialized organs in invertebrates enhancing nutrient absorption.
Step-by-step explanation:
The nutrient delivery systems in both invertebrate and vertebrate animals play a crucial role in the procurement, digestion, absorption, and distribution of nutrients throughout the body. For instance, the human digestive system and the rabbit digestive system, despite both being monogastric, show differences adapted to their diets. Rabbits have a specialized structure called the cecum that allows more efficient digestion of plant materials, which they further digest by re-ingesting soft feces known as cecotrophes.
During digestion in the human small intestine, specifically in the jejunum, most carbohydrates and amino acids are absorbed. The villi and microvilli in the small intestine dramatically increase the surface area for absorption, allowing for efficient transfer of nutrients into the circulatory system. These structures aid in the active transport of most nutrients, a process that requires ATP. In contrast, lipid-soluble nutrients can diffuse through the plasma membrane and enter the lymphatic system via lacteals in the villi.