Give an example of a vertebrate and an invertebrate that both use gizzards. Describe the general structure and function of the gizzard and how it works.

A vertebrate example that uses a gizzard is a bird, such as a chicken. An invertebrate example that has a gizzard is an earthworm (a type of annelid).

The gizzard is a muscular organ that is specialized for grinding and crushing food. It is usually located between the stomach or crop (a food storage area) and the intestine. The gizzard has thick muscular walls that contract to break down food, often using small stones or grit swallowed by the animal to aid in the grinding process. The primary function of a gizzard is the mechanical breakdown of food, making it easier for the digestive enzymes to act upon the food particles and absorb essential nutrients.

The gizzard operates through a combination of muscular contractions and the presence of swallowed grit or stones. When the food reaches the gizzard, the muscular walls of this organ contract and grind the food together with the ingested grit or stones. This grinding effectively breaks down the food into smaller particles. These smaller particles are then passed on to the next stage in the digestive system, where they can be easily acted upon by digestive enzymes to break them down further and facilitate the absorption of essential nutrients. In summary, the gizzard is an adaptation in some animals that enables them to mechanically break down their food for easier digestion and absorption of nutrients. Examples of animals with gizzards include birds like chickens and invertebrates like earthworms.