Plant Tissue Essay

721 Words3 Pages
Chapter 2. Animal Tissues Animals are multicellular heterotrophs whose cells lack cell walls. At some point during their lives, all animals are capable of movement, although not all animals have muscles they use for this. In the most commonly encountered animals, the mobile stage is the adult, although some animals (such as corals and sponges) have sessile (or nonmobile) adult phases and mobile juvenile forms. Both animal and plant evolutionary history show the development of multicellularity and the move from water to land (as well as a secondary adaptation back to water, for example dolphins, whales, duckweed, and elodea). Animals developed external or internal skeletons to provide support, skin to prevent or lessen water loss, muscles that allowed them to move in search of food, brains and nervous systems for integration of stimuli, and internal digestive systems. Organs in animals are composed of a number of different tissue types. For example, the stomach has epithelial tissue making linings and secreting gastric juices, connective tissues. Plants are simpler organisms than animals, having three organ systems and fewer organs than do vertebrate animals. Organs are composed of tissues, which are in turn composed of cells. Plants have three tissue types: ground, dermal, and vascular. Animals have four: epithelial, connective, muscle, and bone. EPITHELIAL TISSUE Epithelial tissue is made of closely-packed cells arranged in flat sheets. Epithelia form the surface of the skin and line the various cavities and tubes of the body. The epithelia that form the inner lining of blood and lymph vessels are called endothelia. The apical surface of epithelial cells is exposed to the "external environment", the lumen of the organ or the air. The basolateral surface is exposed to the internal environment (ECF). The entire sheet of epithelial cells is attached
Open Document