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Cells & Viruses
Quiz by Rachel Sawyer
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Unit 2- Cells & VirusesFLASHBACK FRIDAY cells/viruses/cell transport/biomoleculesCells vs VirusesViruses & CellsViruses vs CellsAnimal Cells, Plant Cells, Fungi, Protoctists and VirusesUnderstanding the differences between bacteria and viruses is important because they affect our health differently. In this study guide, we'll explore the key distinctions between these two microorganisms. Section 1: Bacteria What are Bacteria? Bacteria are tiny, single-celled living organisms. They are found everywhere, including in soil, water, and inside our bodies. Shape and Structure: Bacteria have different shapes like rods, spheres, and spirals. They have a cell wall that surrounds their cell membrane. Reproduction: Bacteria reproduce by dividing in half, a process called binary fission. This allows them to multiply quickly. Living or Nonliving: Bacteria are considered living because they can grow, reproduce, and respond to their environment. Section 2: Viruses What are Viruses? Viruses are smaller than bacteria and are not considered living organisms. They are made up of genetic material (either DNA or RNA) surrounded by a protein coat. Shape and Structure: Viruses come in various shapes but are much simpler than bacteria. They lack the cell structures found in bacteria. Reproduction: Viruses cannot reproduce on their own. They need a host cell (like a human cell) to replicate and make more viruses. Living or Nonliving: Viruses are considered nonliving because they cannot perform life processes without a host cell. Section 3: Differences Now, let's compare bacteria and viruses: Size: Bacteria are larger than viruses. Living or Nonliving: Bacteria are living organisms. Viruses are non-living entities. Reproduction: Bacteria reproduce on their own through binary fission. Viruses need a host cell to replicate. Structure: Bacteria have complex structures with cell walls. Viruses are simpler, consisting of genetic material and a protein coat. Treatment: Bacterial infections are treated with antibiotics. Viral infections are typically managed with antiviral medications (if available) or through the body's immune response. Section 4: Examples Examples of bacteria-related and virus-related illnesses: Bacterial Infections: Strep throat, Urinary tract infections (UTIs), Tuberculosis Viral Infections: Influenza (Flu), Common cold, HIV/AIDS Conclusion: Understanding the differences between bacteria and viruses can help us stay healthy and make informed decisions about treatment. Remember that while bacteria can be both helpful and harmful, viruses rely on our cells to replicate and cause infections.Some substances, such as macromolecules and nutrients, are too large to pass through the cell membrane by the transport processes you have studied so far. Cells employ two other transport mecha- nisms—endocytosis and exocytosis—to move such substances into or out of cells. Endocytosis and exocytosis are also used to transport large quantities of small molecules into or out of cells at a single time. Both endocytosis and exocytosis require cells to expend energy. Therefore, they are types of active transport. Endocytosis Endocytosis (EN-doh-sie-TOH-sis) is the process by which cells ingest external fluid, macromolecules, and large particles, including other cells. As you can see in Figure 5-7, these external materials are enclosed by a portion of the cell’s membrane, which folds into itself and forms a pouch. The pouch then pinches off from the cell membrane and becomes a membrane-bound organelle called a vesicle. Some of the vesicles fuse with lysosomes, and their con- tents are digested by lysosomal enzymes. Other vesicles that form during endocytosis fuse with other membrane-bound organelles. Two main types of endocytosis are based on the kind of material that is taken into the cell: pinocytosis (PIEN-oh-sie-TOH-sis) involves the transport of solutes or fluids, and phagocytosis (FAG-oh-sie-TOH-sis) is the movement of large particles or whole cells. Many unicellular organisms feed by phagocytosis. In addition, certain cells in animals use phagocytosis to ingest bacteria and viruses that invade the body. These cells, known as phagocytes, allow lysosomes to fuse with the vesicles that contain the ingested bacteria and viruses. Lysosomal enzymes then destroy the bacteria and viruses before they can harm the animal. CYTOSOL EXTERNAL ENVIRONMENT During endocytosis, the cell membrane folds around food or liquid and forms a small pouch. The pouch then pinches off from the cell membrane to become a vesicle. FIGURE 5-7 vesicle from the Latin vesicula, meaning “bladder” or “sac” Word Roots and Origins www.scilinks.org Topic: Endocytosis Keyword: HM60505 mb06se_homs02.qxd 5/18/07 11:03 AM Page 105 106 CHAPTER 5 1. Explain the difference between passive trans- port and active transport. 2. What functions do carrier proteins perform in active transport? 3. What provides the energy that drives the sodium-potassium pump? 4. Explain the difference between pinocytosis and phagocytosis. 5. Describe the steps involved in exocytosis. 6. How do endocytosis and exocytosis differ? How can that difference be seen? CRITICAL THINKING 7. Analyzing Information During intense exercise, potassium tends to accumulate in the fluid surrounding muscle cells. What membrane protein helps muscle cells counteract this tendency? Explain your answer. 8. Evaluating Differences How does the sodium- potassium pump differ from facilitated diffusion? 9. Relating Concepts The vesicles formed during pinocytosis are much smaller than those formed during phagocytosis. Explain. SECTION 2 REVIEW Vesicle Cell membrane EXTERNAL ENVIRONMENT CYTOSOL During exocytosis, a vesicle moves to the cell membrane, fuses with it, and then releases its contents to the outside of the cell. FIGURE 5-8 INSIDE OF CELL Vesicle OUTSIDE OF CELL Exocytosis Exocytosis (EK-soh-sie-TOH-sis) is the process by which a substance is released from the cell through a vesicle that transports the sub- stance to the cell surface and then fuses with the membrane to let the substance out of the cell. This process, illustrated in Figure 5-8, is basically the reverse of endocytosis. During exocytosis, vesi- cles release their contents into the cell’s external environment. Figure 5-8 also shows a photo of a vesicle during exocytosis. Cells may use exocytosis to release large molecules such as pro- teins, waste products, or toxins that would damage the cell if they were released within the cytosol. Recall that proteins are made on ribosomes and packaged into vesicles by the Golgi apparatus. The vesicles then move to the cell membrane and fuse with it, deliver- ing the proteins outside the cell. Cells in the nervous and endocrine systems also use exocytosis to release small molecules that control the activities of other cells.