key term - Gills

Definition

Gills are specialized respiratory organs found in many aquatic organisms that facilitate gas exchange by extracting oxygen from water. They consist of thin filaments rich in blood vessels, maximizing surface area for efficient oxygen uptake and carbon dioxide release.

5 Must Know Facts For Your Next Test

1. Gills are primarily composed of filaments and lamellae, which increase the surface area for gas exchange.
2. In molluscs like bivalves, gills also play a role in filter-feeding by trapping food particles.
3. Annelids such as polychaetes have parapodia with gill-like structures for respiration.
4. The efficiency of gills depends on the countercurrent exchange mechanism, where blood flows opposite to the direction of water, enhancing oxygen absorption.
5. Some molluscs, like cephalopods, use muscular contractions to actively pump water over their gills.

Review Questions

Related terms

Lamellae: Thin plate-like structures within gills that enhance surface area for gas exchange.

Parapodia: Paired appendages found in polychaete annelids that often contain gill-like structures for respiration.

Countercurrent Exchange:

A mechanism where fluids flow in opposite directions to maximize transfer rates, crucial in enhancing the efficiency of gas exchange in gills.