Copy of SECTION 205 NEW UNIT B CELLS & SYSTEMS GR 8 SCIENCE PDF

Unicellular Organisms Reproduce. When they reach the limits of their size, like the amoeba, unicellular organisms reproduce. Amoeba do this by dividing into two, which results in two smaller, identical copies of each organism. Your cells reproduce this way, too. That’s how, for example, your body re...

Unicellular Organisms Reproduce. When they reach the limits of their size, like the amoeba, unicellular organisms reproduce. Amoeba do this by dividing into two, which results in two smaller, identical copies of each organism. Your cells reproduce this way, too. That’s how, for example, your body replaces the 50 000 000 or so skin cells that it naturally loses each day! Your body cells also reproduce to repair tissues that get damaged. This process is called mitosis. Multicellular Organisms have Specialized Cells You and most other multicellular organisms are made up of specialized cells. This means that there are various kinds of cells, and each kind carries out a specific function or functions needed to support life. For example, the function of your red blood cells is to carry oxygen to all cells of your body. To do this, the red blood cells often must travel through extremely small blood vessels. Their thin, pliable disc shape enables them to do this. Red blood cells do not reproduce in the same way as skin cells. When red blood cells mature they lose their nucleus. Since the nucleus controls cell division (among other functions), red blood cells can’t reproduce by simply dividing to make more of themselves. The only way your body can make more red blood cells is by relying on specialized tissues in another body system. Most bones of the skeletal system contain a type of connective tissue called marrow, with specialized cells that make red blood cells. Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in. Red blood cells are responsible for carrying oxygen and carbon dioxide. Platelets are responsible for blood clotting. White blood cells are part of the immune system and function in immune response. bone marrow Types of Tissue Epithelial tissue covers the surface of your body and the outside of your organs. It also lines the inside of some of your organs such as the intestine. Makes up the brain, spinal cord, and nerves. Allows you to move. One type of muscle allows you to move your body. Cardiac muscle tissue pumps blood through your heart, and smooth muscle moves food along your intestine. Supports and connects different parts of the body. Blood is a connective tissue and so are fat, cartilage, bones, and tendons.