Organizing Life on Earth

A diagram showing how species are related through common ancestors based on similarities and differences.

Archaea, Bacteria, and Eukarya. These are the broadest categories in the tree of life.

The science of classifying organisms into groups based on shared characteristics.

A two-part scientific naming system (Genus species).

A group of one or more organisms seen by taxonomists to be a unit.

Last Universal Common Ancestor. Oldest common ancestor of all life.

Groups that share an immediate common ancestor.

Branch points (nodes) represent where species diverge.

Similar body parts in different species due to shared ancestry.

Similar body parts in different species due to similar function, not shared ancestry.

Unrelated species developing similar traits due to similar environments.

Related species developing different traits due to different environments.

Body parts that have lost their original function due to evolution.

Body plan where any cut through the center divides the organism into mirror-image halves (like a pie).

Body plan where only one cut divides the organism into mirror-image halves (like a human).

Concentration of sensory organs and a brain in the head region.

Animals lacking a body cavity (coelom) between the gut and outer body wall.

Animals with a body cavity (coelom) that is not fully lined by mesoderm.

Animals are eukaryotic, multicellular organisms with complex tissues, heterotrophic, and mostly motile. They commonly reproduce sexually with a fixed body plan.

The four main types of tissue are epithelial, connective, muscle, and nervous tissue. Each tissue has specific structure and function.

Asymmetrical: No symmetry (e.g., sponges). Radial Symmetry: Symmetry around a central axis (e.g., jellyfish). Bilateral Symmetry: Divisible into symmetrical halves on either side of a unique plane (e.g., humans).

Germ layers are layers of cells in the embryo that develop into tissues and organs.

Diploblast organisms have two germ layers (ectoderm and endoderm), associated with radial symmetry. Triploblast organisms have three germ layers (ectoderm, mesoderm, and endoderm), associated with bilateral symmetry.

A coelom is a fluid-filled body cavity lined with mesoderm. There are three types: acoelomate (no coelom), pseudocoelomate (partially lined), and eucoelomate (fully lined).

Protostome: Mouth develops from the blastopore, spiral cleavage (e.g., mollusks, annelids). Deuterostome: Anus develops from the blastopore, radial cleavage (e.g., echinoderms, chordates).

Sponges belong to the phylum Porifera. These organisms are asymmetrical, lack cephalization, have pores for water flow, and are filter feeders.

A group of cells with a similar structure and function, working together to perform a specific task.

A type of tissue that covers and protects the body's surfaces, lines internal organs, and forms glands.

A type of tissue that supports and connects body parts, providing structure and flexibility. Examples include bone, cartilage, blood, and fat.

A type of tissue responsible for movement and contraction. Three types exist: skeletal, smooth, and cardiac.

A type of tissue responsible for transmitting signals and coordinating body functions, made up of neurons.

Cephalization is the concentration of sensory organs and a brain in the head region of an animal. It allows for better processing of information and more efficient responses to stimuli.

Acoelomates lack a body cavity. Pseudocoelomates have a body cavity partially lined by mesoderm. Eucoelomates have a body cavity fully lined by mesoderm. These differences affect organ development and support.

Chordates share four key features at some point in their life: notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail.

Some major phyla include: Cnidaria (jellyfish), Platyhelminthes (flatworms), Nematoda (roundworms), Arthropoda (insects), Mollusca (snails), Annelida (earthworms), Echinodermata (starfish), and Chordata (vertebrates).

The rhythmic sequence of contraction (systole) and relaxation (diastole) of the heart chambers, ensuring blood circulation.

Electrical impulses, generated by specialized cells in heart tissue (like the SA node), trigger the heart's contractions, coordinating the pumping action.

The sinoatrial (SA) node acts as the heart's pacemaker, initiating the electrical impulse. The atrioventricular (AV) node delays the impulse, allowing the atria to fully contract before the ventricles.

A network of glands that produce and release hormones into the bloodstream, regulating various bodily functions.

Hormones travel through the bloodstream and bind to specific receptors on target cells, triggering a response (e.g., changing cell activity).

The maintenance of a stable internal environment in a living organism, despite external changes.

The process of maintaining a stable internal body temperature.

Ectotherms rely on external sources of heat (e.g., sun, environment), while endotherms generate their own heat internally.

Vasodilation widens blood vessels, increasing blood flow and heat loss, while vasoconstriction narrows blood vessels, reducing blood flow and conserving heat.

A mechanism where heat is transferred between fluids flowing in opposite directions, maximizing heat retention.

The process of maintaining the appropriate water and salt balance in an organism.

Open systems exchange fluids with their environment, while closed systems maintain a separate internal environment.

The body system responsible for removing waste products, excess fluids, and salts from the body.