BIOl 152 1st Edition Lecture 21 Outline of Last Lecture I Non specific barriers II Acquired Adaptive barriers III Humeral immune response IV Cell mediated immune response Outline of Current Lecture V Embryology VI Sponges Porifera VII Cnideria Nettles Current Lecture I Embryology Embryology is the study of embryonic development and includes several processes Fertilization occurs when one sperm cell enters the egg cell and forms a diploid single cell called a zygote The zygote then undergoes mitosis and the nucleus is divided making the zygote a multicellular organism this process of becoming multicellular is known as cell cleavage After the zygote has divided it is referred to as an embryo The blastula stage refers to the stage where the embryonic cells form a one layered ball of cells After the blastula stage the embryo enters the gastrula stage and the cells are rearranged by folding in on each other forming a two layered ball of embryonic cells The outer layer formed is known as ectoderm the middle germ layer not found in all animals is the mesoderm and the inner layer is called the endoderm The ectoderm gives rise to skin and nerves the mesoderm gives rise to muscles and the endoderm gives rise to the digestive track and digestive structure II Sponges Porifera There are over 9000 species of sponges there are both marine saltwater and freshwater species They are sessile or immobile staying in one place for the duration of their lives They are filter feeders where they filter water and obtain organic molecules from the filtered water Sponges contain three tissue layers the mesohyl the porocyte and the spongocoel The mesohyl layer contains connective tissue and stem cells the porocyte These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute creates tubes and the spongocoel is the inner part of the sponge The marine sponges act as osmo conformers because the concentration of solutes inside the sponge is the same as the environment Freshwater sponges have a higher solute concentration inside than the environment so they gain water III Cnideria The Cnideria includes hydras jellyfishes sea anemones and corals and most of the species in this group are marines with some freshwater species These organisms are diploblastic because they contain both an ectoderm and an endoderm They possess radial symmetry where their bodies are symmetrical around a central axis There are two body morphologies the polyp which is sedentary and the medusa which have adapted to swim or float The Cnideria have epithelial tissue a gastro vascular cavity lined by the gastro dermis and the mesoglea these structures function for digestion These organisms sting when threatened and release neurotoxins and toxins that break cells