Gas exchange primarily occurs in the alveoli, which are tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.

The main function of the skeletal system is to provide support and protection for the body's organs and tissues.

Nephridia are excretory organs in annelids that help in the removal of waste products from the body.

The primary role of the circulatory system is to transport nutrients, gases, hormones, and waste products throughout the body.

Natural selection is the process by which organisms that are better adapted to their environment tend to survive and reproduce.

Echinoderms exhibit radial symmetry, which means their body parts are arranged around a central axis.

Mammals are characterized by the presence of hair or fur, which is a key feature distinguishing them from other animal groups.

Feathers are not a characteristic of reptiles; they are found in birds, which are a separate class of animals.

The pancreas is responsible for producing insulin, a hormone that regulates blood sugar levels.

Sexual reproduction involves the fusion of male and female gametes, leading to genetic diversity in offspring.