How is the gastrovascular cavity of a Planaria similar to the gastrovascular cavity of Hydra? How does it differ? Does it seem likely that Planaria would have a circulatory system?
The Correct Answer and Explanation is:
Answer:
The gastrovascular cavity of a Planaria is similar to that of a Hydra in that both serve the dual purpose of digestion and distribution of nutrients throughout the body. However, they differ in structure and complexity. It is unlikely that Planaria would have a circulatory system, and here’s why.
Explanation
Both Planaria and Hydra are simple invertebrates that use a gastrovascular cavity to carry out digestion and nutrient transport. In both organisms, this cavity acts as a central location where food is digested extracellularly. Enzymes are released into the cavity, breaking down the food, and then the cells lining the cavity absorb the nutrients. Because these animals lack complex organ systems, this cavity plays a critical role in meeting their basic metabolic needs.
The similarity lies in their function: the gastrovascular cavity in both organisms helps digest food and spread nutrients to body cells. Additionally, both organisms have only one opening for the cavity, which serves as both the mouth and the anus.
The difference lies mainly in their body structure and the arrangement of the cavity. Hydra has a simple, sac-like body plan with a single, undivided gastrovascular cavity, making it radially symmetrical. In contrast, Planaria has a more complex, branched gastrovascular cavity, which extends through much of the body. This branching allows it to distribute nutrients more efficiently to its bilaterally symmetrical body.
Because of its flat body and extensive branching of the gastrovascular cavity, Planaria does not need a circulatory system. Nutrients and gases can diffuse directly to cells due to the short distances within its thin, flat body. A circulatory system becomes necessary only in larger, thicker organisms where diffusion alone is insufficient. Therefore, it seems unlikely that Planaria would need or evolve a circulatory system, given its size, shape, and efficient use of its gastrovascular cavity.
