[Campbell Biology P.740] A student is studying the feeding and digestive processes in cnidar... | Practice Question

A student is studying the feeding and digestive processes in cnidarians. Which of the following descriptions accurately represents how cnidarians capture and digest their prey?

  • A: Cnidarians use choanocytes to filter-feed, and digestion is primarily intracellular within these cells.
  • B: Prey is captured by nematocysts on tentacles and pushed into the gastrovascular cavity, where enzymes begin digestion, and final digestion occurs intracellularly in gastrodermal cells.
  • C: Digestion in cnidarians is entirely extracellular, occurring solely within the gastrovascular cavity before nutrients are absorbed.
  • D: Cnidocytes are used for locomotion, not prey capture, and food is absorbed directly through the body surface.

Explanation

The text states: 'Cnidarians are predators that often use tentacles arranged in a ring around their mouth to capture prey and push the food into their gastrovascular cavity, where digestion begins. Enzymes are secreted into the cavity, thus breaking down the prey into a nutrient-rich broth. Cells lining the cavity then absorb these nutrients and complete the digestive process; any undigested remains are expelled through the cnidarian's mouth/anus. The tentacles are armed with batteries of cnidocytes... Specialized cnidae called nematocysts contain a stinging thread that can penetrate the body surface of the cnidarian's prey.' This confirms both extracellular and intracellular digestion steps.