Peroxisomes are membranous sacs that contain powerful oxidase enzymes. These enzymes use oxygen to detoxify harmful or poisonous substances. Mitochondria a threadlike organelles which can continuously change shape. Mitochondria are the site of cellular respiration, in which oxygen is used to break down foods and produce energy. Because mitochondria provide energy, they are referred to as the powerhouse of the cell. The centrioles are paired organelles that lie close to the nucleus. They are rod-shaped bodies that lie at right angles to each other. The centrioles play a key role in the division of nuclear elements during cell division.
Epithelial tissue Epithelial tissue, or epithelium, is the lining, covering and glandular tissue of the body. Glandular epithelium forms various glands in the body. Covering and lining epithelium covers all free body surfaces and contains versatile cells. These tissues form both the outer layer of the skin as well as the lining of body cavities. Figure 4 describes the different types of epithelium:
Figure 4 Since epithelial tissue forms the boundaries between our bodies and the outside world, all substances given off or received by the body must pass through the epithelium. Its functions, therefore, include protection, absorption, filtration, and secretion.
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