Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times. What changes in digestive structure and function are associated with the evolution of herbivory? Which of the following is true of the digestive tracts of minnows? a. They are incomplete but have both a mouth and an anus. b. They are complete, facilitating compartmentalization of digestion in different organs. c. They are incomplete, with no accessory organs. d. They are complete and include a large gastrovascular cavity.

Verified step by step guidance

1. Step 1: Let's first understand the difference between carnivorous and herbivorous digestive systems. Carnivores, like minnows, typically have a shorter digestive tract because meat is easier to digest than plant material. Herbivores, on the other hand, have a longer digestive tract to allow for the breakdown of complex carbohydrates found in plants.
2. Step 2: The evolution of herbivory in minnows would likely involve changes to their digestive system to accommodate a plant-based diet. This could include the development of a longer digestive tract, the evolution of specialized structures for breaking down plant material, and changes in gut microbiota to help digest plant material.
3. Step 3: Now, let's look at the options for the digestive tracts of minnows. An incomplete digestive tract is one where the mouth and anus are the same opening, while a complete digestive tract has separate openings for the mouth and anus.
4. Step 4: Minnows, like most fish, have a complete digestive tract. This allows for the compartmentalization of digestion, with different parts of the tract specialized for different functions. Therefore, option b. 'They are complete, facilitating compartmentalization of digestion in different organs.' is correct.
5. Step 5: The other options are incorrect because minnows do not have an incomplete digestive tract (options a and c), and they do not have a large gastrovascular cavity (option d). A gastrovascular cavity is a characteristic of simpler organisms like cnidarians (jellyfish, sea anemones, etc.), not fish.