Evolution of Organ Systems As organisms evolved their body systems became more complex

Body Symmetry Complex animals tend to have high levels of cell specialization and internal body organization, bilateral body symmetry, a front end or head with sense organs, and a body cavity. With the exception of sponges, every kind of animal exhibits some type of body symmetry in its anatomy, or body structure.

Body Symmetry Asymmetry radial symmetry bilateral symmetry no planes can be drawn through the body and create equal halves radial symmetry similar to that of a bicycle wheel, in which any number of imaginary planes can be drawn through the center, each dividing the body into equal halves. bilateral symmetry a single imaginary plane can divide the body into two equal halves.

Body Symmetry Radial Bilateral

Body Cavity Most complex animal phyla have a true coelom that is lined completely with tissue derived from mesoderm.

Body Cavity Acoelomates Pseudocoelomates Coelomates meaning that no coelom, or body cavity, forms between the germ layers. Pseudocoelomates body cavity lined partially with mesoderm (roundworms) Coelomates   completely with tissue derived from mesoderm.

Body Cavity Comparison

Skeletal System Usually one of three main kinds of skeletal systems: hydrostatic skeletons, exoskeletons, or endoskeletons.

Skeletal System No skeleton Hydrostatic skeleton Exoskeleton instead spicules (sponge) or some other form of support (muscles) Hydrostatic skeleton muscles surround a fluid-filled body cavity that supports the muscles. When the muscles contract, they push against fluid in the body cavity, causing the body to change shape. Exoskeleton external skeleton, is a hard body covering made of chitin. Endoskeleton structural support located inside the body.

Skeletal system Hydrostatic skeleton Endoskeleton

Respiratory System Respiratory organs have large surface areas that are in contact with the air or water. Also, for diffusion to occur, the respiratory surfaces must be moist.

Respiratory System Diffusion Gills Book lungs Spiracles Lungs respire through their skins Gills feathery structures that expose a large surface area to the water. Gills are rich in blood vessels that bring blood close to the surface for gas exchange. Book lungs parallel, sheetlike layers of thin tissues that contain blood vessels. Spiracles in insects, air enters the body through openings called spiracles. It then enters a network of tracheal tubes, where gases diffuse in and out of surrounding body fluids. Lungs Inhaling brings oxygen-rich air from outside the body through the trachea (TRAY-kee-uh) and into the lungs. The oxygen diffuses into the blood inside the lung capillaries.

Respiratory System Gills Book Lungs

Respiratory System Spiracles Lungs

Excretory System Most animals have an excretory system that rids the body of metabolic wastes while controlling the amount of water in the tissues.

Excretory System Diffusion Nephridia Malpighian Tubes Kidneys ammonia diffuses from their body tissues into the surrounding water. Nephridia annelids and mollusks, urine forms in tubelike structures called nephridia. Fluid enters the nephridia through openings called nephrostomes. Urine leaves the body through excretory pores. Malpighian Tubes saclike organs that convert ammonia into uric acid. Kidneys urea is removed from the bloodstream along with other metabolic wastes Cloaca- frogs only one tube for solid and liquid waste Humans- two tubes one for solid waste the other for liquid waste

Excretatory System Cloaca Malpighian Tubes

Most vertebrates reproduce sexually Reproductive System Most invertebrates reproduce sexually during at least part of their life cycle. Depending on environmental conditions, however, many invertebrates may also reproduce asexually. Most vertebrates reproduce sexually

Reproductive System Asexually Sexually only need one need two Internal eggs are fertilized inside the female's body. External eggs are fertilized outside the female's body

Circulatory System Most complex animals move blood through their bodies using one or more hearts and either an open or closed circulatory system.

Circulatory System Diffusion Open system Closed system blood is only partially contained within a system of blood vessels. Instead, one or more hearts or heartlike organs pump blood through blood vessels into a system of sinuses, or spongy cavities. The blood comes in direct contact with the tissues and eventually makes its way back to the heart. Closed system a heart or heartlike organ forces blood through vessels that extend throughout the body. The blood stays within these blood vessels. Materials reach body tissues by diffusing across the walls of the blood vessels. Frog three chamber heart Human four chamber heart

Circulatory System Open System Closed System

Circulatory System Single and Double Loop 23

Human Circulatory System How Does Blood flow?

Digestive System The simplest animals break down food primarily through intracellular digestion, but more complex animals use extracellular digestion.

Digestive System Intracellular Extracellular food is digested inside cells Simple animals such as cnidarians and most flatworms ingest food and expel wastes through a single opening. filter feeders Extracellular food is broken down outside the cells in a digestive cavity or tract and then absorbed into the body. More-complex animals digest food in a tube called the digestive tract. Food enters the body through the mouth, and wastes leave through the anus. One way track Mouth/anus characteristic of roundworms, mollusks, arthropods, and echinoderms Two way track Mouth and anus

Digestive System One way track Two way track

Nervous System Invertebrates show three trends in the evolution of the nervous system: centralization, cephalization, and specialization. Nonvertebrate chordates have a relatively simple nervous system with a mass of nerve cells that form a brain. Vertebrates have a more complex brain with distinct regions, each with a different function.

Nervous System Centralization Cephalization Specialization Nerve Nets consist of individual nerve cells that form a netlike arrangement throughout the animal's body. Cephalization concentration of nerve tissue and organs in one end of the body Vertebrates display a high degree of cephalization, or concentration of sense organs and nerve cells at the front of the body. The head contains a well-developed brain The cerebrum is the “thinking” region of the brain. Specialization specialized sense organs that detect light, sound, chemicals, movement, and even electricity to help them discover what is happening around them.

Comparison and Complexity of Nervous Systems

Human Body Exhibit 31

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