Specialized Cells PDF - Chapter 2

2.9 Specialized Cells In this chapter, you have looked at plant and animal cells as they grow and divide. You have seen that different cells have greater numbers, or few...

2.9 Specialized Cells In this chapter, you have looked at plant and animal cells as they grow and divide. You have seen that different cells have greater numbers, or fewer, of certain organelles depending on the function of the cell. You have also learned how cells sometimes grow out of control, forming tumours. Next you will look at some of the wide variety of different cell types—each with its own special function—that make up the bodies of plants and animals. The cell theory states that every cell comes from a previously existing cell. You started life as a single fertilized egg. A towering maple tree also started as a single cell. The many cells in a complex organism are not all identical, however. Look at your best friend or any other living thing around you: they are made up of cells with different structures and different functions. You can compare a multicellular organism to a large city. The city needs energy, transportation corridors, waste disposal facilities, a police force, and organization to keep everything operating efficiently. Different parts of the city have different purposes, and different businesses in the city meet different needs. Auto mechanics repair damaged cars. Dental hygienists help us keep our teeth healthy. Farmers grow and provide food. The list goes on. You do not expect the same person to repair your car, clean your teeth, and sell you food. Each of these jobs is performed by someone who is trained to do that job: a specialist. Your body has needs similar to those of a city: energy, transportation, waste disposal, and so on. Every cell cannot digest food, fight disease, carry nutrients, and coordinate your body’s movements. Similar to people working specialized cell a cell that can perform a in a city, specialized cells have physical and chemical differences that allow specific function them to perform one job very well. Figure 1 shows some of the different kinds of cells that line the trachea—the tube that carries air from the mouth to the lungs. Notice the orange-stained goblet cells. They contain many Golgi bodies to produce mucus. Cell specialization involves a change in form and in function. Specialized cells can look very different from each other. Figure 1 These specialized cells help to keep dirt out of the lungs. The orange cells are goblet cells. They secrete mucus. The parts that look like green grass are cilia—hair-like extensions of cells. The cilia can move. They move mucus along the trachea to trap and remove any inhaled dust and dirt. 58 Chapter 2 Cells, Cell Division, and Cell Specialization NEL  Animal cells show a wide variety of specializations, as Figure 2 shows. They differ internally as well as externally. Cells such as muscle cells that use a lot of energy, for example, have a lot of mitochondria. Similarly, cells that produce mucus in the intestine have many Golgi bodies. These cells are specialized to perform particular functions. (a) (d) (g) Red blood cells contain hemoglobin that carries Layers of skin cells fit together tightly, cover- Bone cells collect calcium from food and allow oxygen in blood. The cells are smooth so that ing the outside of the body to protect the cells the growth and repair of bones. They build up they can easily pass through the blood vessels. inside and to reduce water loss. bone around themselves, creating the body’s skeleton. (b) (e) (h) Muscle cells are arranged in bundles called White blood cells can move like an amoeba to Sperm cells are able to move independently, muscle fibres. Muscle cells can contract, which engulf bacteria and fight infection. carrying DNA from the male parent to join with makes the fibre shorter and causes bones to an egg cell from the female parent. move. (c) (f) (i) Fat cells have a large vacuole in which to store Nerve cells are long, thin, and have many Some animals that are active mainly at night, fat molecules. This is how the cell stores chemi- branches. They conduct electrical impulses to and others that live deep in the ocean, have cal energy. coordinate body activity. cells that can emit light. These cells are called photophores. Figure 2 A few of the many kinds of specialized cells found in animals NEL 2.9 Specialized Cells 59  Plants also have specialized cells. The structure and function of the cells in a leaf are different from those of the cells in the trunk of a tree. Some of the specialized plant cells are shown in Figure 3. In the next chapters, you will learn how cells work together in complex organisms. Chapter 3 focuses on animals and Chapter 4 on plants. (a) (c) (e) Some plant cells transport water and dissolved Storage cells contain special structures that Photosynthetic cells contain many minerals throughout the plant. store starch, a source of energy for the plant. chloroplasts to collect energy from sunlight to make sugar for the plant. (b) (d) (f) Other cells transport dissolved sugars around Epidermal cells on young roots have hairs that Guard cells in the surface of leaves control the plant. absorb water from the soil. water loss. Figure 3 Plants also have a wide variety of specialized cells. IN SUMMARY All multicellular organisms are made mostly of A specialized cell performs one primary function specialized cells. instead of doing everything an organism needs to Specialized cells have structures that allow them stay alive. to perform specific functions. CHECK YOUR LEARNING 1. Why are complex organisms made up of specialized 4. Every cell in your body came from one fertilized egg cells? K/U cell. What does this tell you about the DNA differences 2. Think about your own body. List at least four activities that between one body cell and another? K/U your body must do to keep you alive. K/U 5. Do plant cells specialize in the same way as animal cells? 3. Choose two specialized cells mentioned in this section. Use examples of each to illustrate your answer. A Compare their structure and function. K/U 6. Why do single-celled organisms not show specialization? K/U 60 Chapter 2 Cells, Cell Division, and Cell Specialization NEL