Humans are classified as which type of organism?

Humans are classified as bipeds because they primarily walk on two legs. This bipedal locomotion is a defining characteristic of the human species, distinguishing them from quadrupeds, which walk on four legs. Bipedalism not only affects movement but also has implications for human physiology, anatomy, and even social behavior, as it has allowed for various adaptations in tool use and communication.

The other options do not accurately classify humans; they either refer to organisms that walk on four legs, lack a backbone, or live in marine environments, which does not apply to humans. Therefore, the classification of humans as bipeds is based on their unique method of locomotion, setting them apart in the animal kingdom.