What is the primary function of a gizzard?

The primary function of a gizzard is to grind feed into finer particles. This specialized muscular organ is particularly crucial for birds and some reptiles, which often lack teeth to chew their food. Instead, the gizzard works by contracting and expanding, utilizing abrasive particles like stones or grit ingested by the animal to help break down tough food materials. This mechanical digestion is essential for properly processing the food before it moves into the intestines, where nutrient absorption occurs.

The other functions mentioned in the other options, such as nutrient absorption or food storage, occur in different parts of the digestive system, like the intestines and crop, not the gizzard. The gizzard's role is purely mechanical and vital for effective digestion in species reliant on it.