biology

• Multicellular organisms have greater capacity for internal specialization than unicellular organisms.
• There are five grades of organization in animals: protoplasm, cell, tissue, organ, organ system.
• Animal tissues can be divided into somatic or body cells and germ cells.
• Tissues are groups of cells with the same structure and perform similar functions.
• There are four major groups of somatic tissues: epithelium, connective, muscular, and nervous.
• Epithelium forms the covering or lining of all free body surfaces.
• Epithelial cells can be structurally classified as squamous, cuboidal, columnar, ciliated, or flagellated.
• Epithelial tissue can be classified as simple, stratified, or pseudostratified.
• Functionally, epithelial tissue can be protective, glandular, sensory, or involved in absorption or filtration.
• Protective epithelium guards animals from external injury and infection.
• Glandular epithelium is specialized for secreting products necessary for use by an animal.
• Connective tissues bind together and support other structures.
• Connective tissues are derived from the mesenchyme, a generalized embryonic tissue.
• Mesenchyme can also differentiate into vascular and smooth muscle.
• Reticular tissue is a framework of stellate reticular cells and fine reticular fibers, found in lymph glands, red bone marrow, the spleen, and other organs.
• Fibrous connective tissue consists of scattered cells, fibers, and two minor cell types (fibroblasts and macrophages), commonly found in tendons, ligaments, muscles, and nerves.
• Adipose or fat tissues contain rounded or polygonal cells with droplets of fat, usually dissolved in prepared microscopic sections, found in the body.
• Cartilage connective tissue is a firm and elastic matrix secreted by small groups of rounded cartilage cells (chondrocytes).
• Cartilage is classified into three types: hyaline, elastic, and fibrocartilage.
• Hyaline cartilage is bluish white, translucent, and homogenous under the light microscope, with fine collagen fibers embedded in the matrix.
• Elastic cartilage contains yellow fibers and is found in the external ears and eustachian tube.
• Fibrocartilage is the most resistant type of cartilage, with a higher proportion of fibers and less matrix. It is found in intervertebral discs, pubic symphysis, and joints subject to severe strains.
• Bone or osseous tissue occurs in the skeletons of bony fishes and land vertebrates, consisting of a dense organic matrix with mineral deposits and calcium carbonate.
• Bone tissue develops either as a replacement for previously existing cartilage or follows embryonic mesenchymal cells.
• Both types of bone tissue are produced by bone cells called osteoblasts, which later mature into osteocytes.
• In mammalian long bones, there are many small tubular concentric lamellae forming cylindrical haversian systems, with walls consisting of several lamellae and a central haversian canal.
• The haversian systems provide channels for blood vessels and nerves, allowing for vascularization of the bone tissue.
• Vascular tissue is a fluid connective tissue composed of white blood cells, red blood cells, platelets, and plasma.
• White blood cells include granulocytes (neutrophils, basophils, eosinophils) and agranulocytes (monocytes and lymphocytes).
• Red blood cells, or erythrocytes, are colored red by the pigment hemoglobin, which serves various functions.
• Red blood cells: Cells responsible for the transport of oxygen, non-nucleated, biconcave and usually round in most mammals, but nucleated, biconvex and oval in other vertebrates.
• Blood platelets: Fragments shed by megakaryocytes in bone marrow, involved in blood clotting.
• Blood plasma: Straw-colored liquid that serves as a transport medium for blood cells and platelets, mostly composed of water.
• Muscular tissues: Most common tissue in the body, made up of elongated cells or fibers specialized for contraction, responsible for movement.
• Muscle fiber: Cytoplasm of a muscle cell, called sarcoplasm, contains contractile elements.
• Muscular tissues can be either voluntary or involuntary.
• Nervous tissues are highly specialized for irritability and conductivity.
• The structural and functional unit of the nervous system is the nerve cell or neuron, which consists of a body containing the nucleus and its processes, the axon and dendrites.
• Plant tissues can be divided into two groups: meristematic tissues, which undergo continuous cell division and contribute to localized growth, and permanent tissues, which develop structural and functional specialization.
• Meristematic cells are continuously dividing and contribute to the growth of plants.