Diversity in Living Organisms

Squirting ink is a defensive action performed by the squid. Since it is an activity rather than a structural body part, it is a behavioral adaptation.

A tail is a physical body part. Using it for balance or movement is a function of that physical structure, making it a physical adaptation.

Bacteria are single-celled organisms, making them unicellular. Cockroaches, sparrows, and mosquitoes are multicellular organisms.

According to the cell theory, all living organisms are composed of one or more cells. This is the fundamental shared characteristic between a single-celled protist and a multicellular tigress.

Cell theory defines the cell as the basic structural and functional unit of all living organisms.

Prokaryotic cells are simple cells that lack a nucleus and membrane-bound organelles. They contain DNA and a cell membrane but are structurally less complex than eukaryotic cells.

Vertebrates are characterized by a spinal column and a distinct head region, which includes paired sensory structures like eyes and ears. These are key developmental features of the subphylum.

Mammals are endothermic, meaning they are capable of regulating their internal body temperature independently of the external environment. This is a defining characteristic of the class Mammalia.

Humans are classified within the Kingdom Animalia, as they are multicellular, eukaryotic, heterotrophic organisms.

Humans are classified as mammals because they have mammary glands, hair, and are endothermic vertebrates.

Eukaryota is the domain for organisms with complex cells containing a nucleus. Prokaryotes, such as bacteria, lack a membrane-bound nucleus.

Endothermic organisms (like mammals and birds) regulate their internal temperature metabolically. Ectothermic organisms rely on external heat sources.

Birds are members of the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, and hollow bones that facilitate flight.

Bacteria are unicellular prokaryotic organisms. They are found in almost every habitat on Earth and are classified by shapes such as cocci (spheres), bacilli (rods), and spirilla (spirals).

Archaea are a domain of single-celled microorganisms that are prokaryotic, similar to bacteria, but possess distinct biochemical and genetic characteristics. They are often found in extreme environments.