Chapter 25 What is an animal? Sections 1 and 2 Typical Animal Characteristics Body Plans and Adaptations Section 1 – Typical Animal Characteristics Characteristics of All Animals: All eukaryotic. All multicellular organisms. All have cells without cell walls. All are heterotrophic. Characteristics of All Animals: All animals must digest their food within individual cells or in an internal cavity. Some of the digested food is stored as fat or glycogen to use as a source of energy at a later time. Characteristics of Some Animals: Most have ways of moving that help them reproduce, obtain food, and protect themselves. Most have specialized cells that form tissues and organs. Characteristics of Some Animals: Some organisms are sessile: Organisms that are permanently attached to a surface. Do not expend much energy to obtain food. Examples: Adult forms of coral and sponges. Development of Animals Most animals reproduce sexually. Development of Animals A zygote is formed when female egg cells are fertilized by male sperm cells. Fertilization may be internal or external. Development of Animals The zygote divides through mitosis to form two cells in a process called cleavage. Once cell division has begun the zygote becomes an embryo. Development of Animals The two cells further divide by mitosis into four cells, and so on, until a cellcovered fluid-filled ball called a blastula is formed. Development of Animals After the formation of the blastula, cell division continues. The cells on one side of the blastula move inward to form a structure made up of two layers of cells with an opening at one end called a gastrula. Development of Animals Gastrula The layer of cells on the outer surface of the gastrula is called the ectoderm and eventually develops into skin and nervous tissue. Development of Animals Gastrula The layer of cells on the inner surface of the gastrula is called the endoderm and eventually develops into the digestive tract and organs for digestion. Development of Animals Gastrula In some animals the cells of the gastrula further divide into a third layer called the mesoderm, located between the ectoderm and the endoderm. The mesoderm eventually forms the muscles, circulatory system, excretory system, and sometimes the respiratory system. Development of Animals Protostomes vs. Deuterostomes When the opening of the gastrula develops into a mouth the animal is called a protostome. Examples: snails, earthworms, and insects. Development of Animals Protostomes vs. Deuterostomes When the mouth of the organism is not developed from the opening to the gastrula, the animal is called a deuterostome. Examples: sea stars, fish, toads, snakes, birds, and humans. Development of Animals Cells in developing embryos continue to differentiate and become specialized to perform different functions. Development of Animals Some embryos develop into miniature forms of adults called juveniles. Development of Animals Some embryos develop inside an egg into an intermediate stage called a larva which has little resemblance to the adult. Inside the egg, the larva is surrounded by a membrane formed right after fertilization. Development of Animals After the juvenile or larval stage the animal passes into the adult stage and cycle begins again. http://www.bozemanscience.com/sc ience-videos/2012/5/6/animals.html Section 2 – Body Plans and Adaptations Symmetry A term used to describe the arrangement of body structures: Asymmetry Radial Symmetry Bilateral Symmetry Asymmetry An animal that is irregular in shape. Asymmetrical animals are often sessile. Example: Sponges Radial Symmetry Animals that can be divided along any plane through a central axis into roughly equal halves. Radial symmetry enables an animal to detect and capture prey coming toward it from any direction. Example: Hydra Bilateral Symmetry Animal can be divided down its length into similar right and left halves. Bilateral Symmetry Bilateral animals have four sides: Anterior or head end (often with sensory organs) Posterior or tail end Dorsal or upper surface Ventral or lower surface Bilateral Symmetry All animals with bilateral symmetry developed from three embryonic cell layers – ectoderm, endoderm, and mesoderm. Bilateral Symmetry Some animals with bilateral symmetry also have fluid-filled spaces inside their bodies in which internal organs are found called body cavities. These cavities allow the animal to grow large because they provide efficient circulation and transportation of fluids and support for organs and organ systems. Bilateral Symmetry Animals with bilateral symmetry can be divided into: Acoelomates Psuedocoelomates Coelomates Bilateral Symmetry Acoelomates: Have no body cavities Have digestive tracts that extend throughout the body. May have been the first group of animals in which organs evolved. The organs are embedded in the solid tissues of the body. Example: Flatworm Bilateral Symmetry Psuedocoelomates: Have a fluid-filled body cavity partly lined with mesoderm that develops between the endoderm and mesoderm Have a one-way digestive tract that has regions with specific functions. Can move quickly because muscles attach to the mesoderm and brace against the rigid, fluid-filled psuedocoelom. Examples: Roundworm Bilateral Symmetry Coelomates: Have a fluid-filled body cavity completely surrounded by mesoderm Have the greatest diversity of all animals. Specialized organs and organ systems develop in the coelom. The digestive tract and other internal organs are attached by double layers of mesoderm and are suspended within the coelom, which cushions and protects them. Animal Protection and Support Exoskeleton Hard covering on the outside of the body that: Provides a framework for support Protects soft body tissues Prevents water loss Provides protection from predators Animal Protection and Support Exoskeleton: The exoskeleton is secreted by the epidermis and extends into the body where it provides a place for muscle attachment. As an animal grows it secretes a new exoskeleton and sheds the old one. Usually found in invertebrates which are animals that do not have a backbone. Examples: Crabs, spiders, dragonflies, beetles Animal Protection and Support Endoskeleton: Covered by layers of cells Provides support for the body Protects internal organs Provides an internal brace for muscles to pull against May be made of calcium carbonate, cartilage, or bone. Animal Protection and Support Endoskeleton: May be found in invertebrates such as sea stars and sea urchins or in vertebrates, which are animals with both an endoskeleton and a backbone, such as fish, amphibians, reptiles, birds, and mammals. Origin of Animals Probably evolved from aquatic, colonial protists in the late Precambrian. All the major body plans that exist today were thought to already be in existence by the beginning of the Cambrian Period 543 million years ago.