What helps direct water over the gills?
The correct answer and explanation is:
Correct Answer: The cilia help direct water over the gills.
Explanation:
In aquatic mollusks like clams, gills are essential for breathing and filtering food. To function properly, gills must have a constant flow of water passing over them. This is where cilia come in. Cilia are tiny, hair-like structures found on the surface of the gills and other internal tissues. These microscopic projections beat in a coordinated manner to create a water current. This current ensures that oxygenated water flows steadily over the gill surfaces, allowing the animal to extract oxygen from the water and release carbon dioxide.
Cilia are particularly important because clams are mostly stationary filter feeders. They do not actively swim to bring in fresh water. Instead, the beating of the cilia provides a mechanism to pull water into the clam’s body through the incurrent siphon. The water then flows across the gills, where gas exchange takes place. In addition to respiration, the gills trap food particles suspended in the water. The cilia also help move these food particles toward the labial palps, which sort and direct them to the mouth.
The movement of water created by cilia plays a dual role: it supports respiration and feeding. This efficient use of water flow allows the clam to thrive in environments where food and oxygen are both suspended in the water. Without the action of cilia, the clam would not be able to move water across its gills effectively, leading to a decrease in oxygen uptake and difficulty in feeding. Thus, cilia are a vital adaptation that supports the survival of clams and similar bivalves in aquatic habitats.