key term - Choanocytes

Definition

Choanocytes are specialized cells found in sponges, belonging to the Phylum Porifera, that play a crucial role in the sponge's feeding and water filtration processes. These cells have a unique structure featuring a flagellum surrounded by a collar of microvilli, which aids in capturing food particles from the water as it flows through the sponge's body. By creating water currents and filtering nutrients, choanocytes are essential for the survival and functioning of sponges.

5 Must Know Facts For Your Next Test

1. Choanocytes are also referred to as collar cells due to their distinctive collar-like structure made up of microvilli surrounding the flagellum.
2. The movement of the flagella in choanocytes generates water flow through the sponge, facilitating both feeding and waste removal.
3. These cells capture food particles like bacteria and plankton through a process called phagocytosis, where they engulf and digest the particles.
4. Choanocytes are believed to share a common ancestry with single-celled protists known as choanoflagellates, indicating an evolutionary link between sponges and more complex animals.
5. In addition to their role in feeding, choanocytes also help maintain the sponge's internal environment by regulating water flow and assisting in gas exchange.

Review Questions

• How do choanocytes contribute to the feeding mechanism of sponges?
  • Choanocytes play a central role in the feeding mechanism of sponges by generating water currents through their flagellar movement. As water flows through the sponge via ostia, food particles such as bacteria are trapped by the microvilli in the collar of choanocytes. This process allows sponges to filter feed efficiently, ensuring they capture enough nutrients for survival.
• Discuss the structural adaptations of choanocytes that make them effective in their role within sponges.
  • Choanocytes possess several structural adaptations that enhance their effectiveness in filtering food from water. The flagellum is crucial for creating water currents, while the collar of microvilli increases the surface area available for trapping food particles. This unique combination allows choanocytes to efficiently capture and engulf small particles, making them vital for the sponge's feeding and overall health.
• Evaluate the evolutionary significance of choanocytes in understanding the transition from simple organisms to more complex metazoans.
  • The evolutionary significance of choanocytes lies in their similarity to choanoflagellates, single-celled organisms that are considered the closest living relatives of animals. This suggests that choanocytes may represent an early adaptation in multicellular organisms that enabled more efficient feeding strategies. By studying choanocytes, researchers can gain insights into how early metazoans evolved from simple, single-celled ancestors into complex organisms with specialized cell types, contributing to our understanding of animal evolution as a whole.

Related terms

Porifera:

A phylum that includes sponges, characterized by a simple body structure with porous bodies and the absence of true tissues and organs.

Ostia: Small pores on the surface of sponges through which water enters, allowing for the circulation of water and the transport of nutrients.

Osculum: The large opening at the top of a sponge where water exits after passing through the sponge's body and being filtered by choanocytes.