Chapter 5 Study Guide - OCR PDF

Ch 8+041 Cu The Working cell 51 2. 3. 7....

Ch 8+041 Cu The Working cell 51 2. 3. 7. 4. 1. 6. 9. 11. 10. o 8. Exercise 2 (Modules 5.3—5.9) Review diffusion and the function of cell membranes by matching each of the phrases on the right with the appropriate mechanisms from the list on the left. Two questio s require more than one answer. 1. Diffusion across a biological membrane A. Diffusion 2. Moves solutes against concentration gradient B. Active transport 3. Any spread of molecules from area of higher concentration C. Osmosis to area of lower concentration D. Phagocytosis 4. Diffusion with the help of a transport protein E. Passive transport 5. Three types of endocytosis F. Facilitated diffusion 6. Engulfing of fluid in membrane vesicles G. Pinocytosis H. Receptor-mediated 7. Diffusion of water across selectively permeable membrane, from hypotonic to hypertonic solution endocytosis I. 8. Transport molecules need ATP to function Exocytosis 9. Enables cell to engulf bulk quantities of specific large molecules 10. How oxygen and carbon dioxide enter and leave cells 11. Two types of passive transport 12. Engulfing of particle in membrane vesicle 13. Fusion of membrane-bound vesicle with membrane, and dumping of contents outside cell 14. How a cell might capture a bacterium 15. Helped by aquaporins 52 Chapter 5 Exercise 3 (Modules 5.4—5.5) Osmosis is an important process that has many effects on living things. Test your under- standing of osmosis by predicting in each of the following cases whether water will enter the cell (In) or leave the cell (Out), or whether there will be no net movement of water (None). Assume that the plasma membrane is permeable to water but not solutes. 1. Cell is exposed to a hypertonic solution. 2. Cell is placed in a salt solution whose concentration is greater than that of the cell contents. 3. Due to disease, the solute concentration of the body fluid outside a cell is less than the solute concentration inside cells. 4. Cell is immersed in an isotonic solution. 5. A single-celled organism is placed in a drop of pure water for examination under a microscope. 6. Cell is immersed in solution of sucrose and glucose whose individual concentrations are less than concentration of solutes in cytoplasm, but whose combined concentration is greater than concentration of solutes in cytoplasm. 7. Solute concentration of a cell is greater than the solute concentration of the surrounding fluid. 8. Cellis exposed to a hypotonic solution. 9. Concentration of solutes in a cell's cytoplasm equals the solute concentration of extracellular fluid. 10. Cytoplasm is more dilute than surrounding solution. Exercise 4 (Modules 5.1—5.9) Try to picture membranes and their functions close up by completing the following story. Your first mission as a Bionaut requires you to enter a blood vessel and observe the structureand functions of cell membranes. You step into the water-filled chamber of the Microtron, which quickly shrinks you to a size much smaller than a red blood cell. You tumble through the tunnel-like needle and into a blood vessel in the arm of a volunteer. Huge, rubbery red blood cells slowly glide past. Floating in the clear, yellow- ish blood plasma, you switch on your headlamp and examine the epithelial cells of the vessel wall. Their plasma membranes seem made of millions of small balloons. These are the hydrophilic "heads" of the I molecules that make up most of the membrane surface. Through the transparent surface, you can see their flexible, 2 tails projecting inward toward the interior of the membrane and beyond them an inner layer of 3 molecules with their tails pointing toward you. Here and there are globular 4 molecules embedded in the membrane; some rest lightly on the surface, but most project all the way into the inte- The membrane is indeed a 5 rior of the cell. mosaic; the proteins are embedded like the pieces of a picture, but you can see that they are free to move around. You push on one of the proteins, and it bobs like an iceberg. Some of the phospholipids and proteins have chains of sugar molecules attached to them, forming 6 and 7 These are the molecules that act as cell. 8 tags. You notice that one of the proteins has a dimple in its surface. Just then a small, round molecule floating in the plasma nestles in the dimple. The mole- cule is a hormone, a chemical signal, and the dimpled protein is the 9 that enables the cell to respond to it. you can see the sparkle and shimmer of many molecules, In your light beam, large and small, in the blood and passing through the cell membrane. Oxygen is moving  The Working cell 53 from the plasma, where it is more concentrated, to the cell interior, where it is less con- centrated. This movement is 10 ; when it occurs through a biological membrane, it is called 11 transport. Similarly, carbon dioxide is flowing out of the cell, down its 12 gradient, from the cell Interior, where it is 13 concentrated, to the blood, where it is 14 concentrated. You note that water molecules are passing through the membrane equally in cell and in the blood must be both directions. The total concentration of solutes in the equal; the solutions must be 15 You signal the control team to inject a. small amount of concentrated salt solution into the blood, making the blood slightly 16 relative to the cell contents. This causes water to flow 17 the cell, until the two solutions are again in equilibrium. This dif- fusion of water through a 18 permeable membrane is calledi 19 Some sugar molecules floating in the blood are simply too large and polar to pass easily through the plasma membrane. The sugar molecules simply bounce off, unless they happen to pass through pores in special 20 proteins. This is a type of passive transport, because the molecules move down a concen&ation gradient without the expenditure of 21 Because transport proteins help out, it is called 22 diffusion. Your chemscanner detects a high concentration of potassium ions inside the cell. Transport proteins here and there in the membrane are able to move potassium into the cell against the concentration gradient. This must be 23 transport; the cell expends 24 to provide energy to "pump" the potassium into the cell. Suddenly there is a tug at your foot. You look down to see your flipper engulfed by a rippling membrane. A white blood cell the size of a house quickly pins you against the vessel wall. The phospholipids of its membrane are pressed against your face mask. The cell is engulfing you, protecting the body from a foreign invader! Taking in a sub- stance in this way is called 25 more specifically 26 , if the substance is a solid particle. Suddenly the pressure dimin- ishes, and you are inside the white blood cell, floating free in a membrane-enclosed bag, or 27 Another sac is approaching; it is a 28 of digestive enzymes. You manage to get your legs outside of the vacuole and move it back toward the inner surface of the cell membrane. As the vacuole fuses with the plasma membrane, you tear your feet free and swim away from the voracious cell, realizing that 29 expelled you almost as fast as endocytosis trapped you! You swim to the exit point, and the control team removes you by syringe. You are soon back in the lab, restored to normal size, and telling your colleagues about your close call. 54 Chapter 5 Exercise 5 (Modules 5.10—5.14) After reading Modules 5.10—5.14, review energy, chemical reactions, and the function of enzymes by filling in the blanks in the following story. If you were to stop eating, you would probably starve to death in weeks or months. you were unable to breathe, you would die in minutes. Organisms need the If energy that is released when food and oxygen combine. This energy is used not only to move the body but also to keep it from falling apart. Energy is the ability to perform 1 The sun is the source of 2 the energy that sustains living things. Sunlight is pure energy, en- ergy of movement that is actually doing work. In the process of photosynthesis, plants are able to use the energy of sunlight to produce food molecules. This process obeys the laws of 3 the principles that govern energy transformations. Plants do not make the energy in food. According to the 4 law of thermody- namics, energy can be 5 or transferred, but it cannot be created or de- stroyed. In photosynthesis, no energy is created. Rather, the plant transforms the energy of sunlight into chemical energy, a form of 6 energy, stored in the chemical bonds of molecules of glucose. No energy change is 100% efficient, and the changes that occur in photosynthesis are no exception to this rule. Some of the energy of sunlight is not stored in glucose, but rather is converted to 7 which is random molecular motion. This , energy is "lost" as far as the plant is concerned, and this random motion contributes to the disorder of the plant's surroundings. The 8 law of thermodynamics 9 says that energy changes are always accompanied by an increase in a measure of disorder. One of the reasons living things need a constant supply of energy is to counter this natural tendency toward disorder. 10 The products of photosynthesis contain potential energy 11 re- than the reactants. This means that, overall, photosynthesis is an action. Such a reaction consumes energy, which in photosynthesis is supplied by the sun. Photosynthesis produces food molecules, such as glucose, which store energy. An animal might obtain this food by eating a plant or an animal that has eaten a plant. The food molecules enter the animal's cells, where their potential energy is released in the process of cellular respiration. The products of this chemical reaction (actually a se- ries of reactions) contain less potential energy than the reactants. Therefore, cellular res- 12 13 energy. In fact, this piration is an process; it is the same overall change that occurs when glucose in a piece of wood or paper burns in air. When paper burns, the energy escapes as the heat and light of the flames. In a cell, the reaction occurs in a more controlled way, and some of the energy is captured for use by the cell. Energy released by the exergonic ''burning" of glucose in cellular respiration is used to make a substance called 14. A molecule of 15 and a 16 group are joined to form each molecule of ATP. This is an ender- gonic reaction, because it takes energy to assemble ATP. The covalent bond connecting the phosphate group to the rest of the ATP molecule is unstable and easily broken. This energy. The 18 of arrangement of atoms stores 19 ATP is an exergonic reaction. When ATP undergoes hydrolysis, a  The Working cell 55 is removed, ATP becomes 20 and energy is released. Thus, ATP is a kind of energy "currency" that can be used to perform cellular 21 There are three kinds of cellular work: 22 23 24 , and Most cellular activities depend on ATP energizing other mole- cules by transferring its phosphate group to them—a process called when ATP causes molecules in This happens in mechanical work, muscle cells to move. It when ATP is used should be noted that energy is not destroyed to do work. When an ATP molecule is hydrolyzed to make muscles move, some of its en- ergy moves the body, and some ends up as random molecular motion, or 26. Similarly, ATP is used to move substances through 27 this is called transport work. A less obvious but important function of ATP is supplying the energy for fight- ing the natural tendency for a system to become disordered. A cell constantly needs to manufacture molecules to replace ones that are used up or damaged. This is chemical work. Building a large molecule from smaller parts is an 28 reacåon. Energy released by the exergonic hydrolysis of ATP is used to drive essenåal endergonic reactions. The linking of exergonic and endergonic processes is called energy 29 and ATP is the critical connection between the processes that re- lease energy and those that consume it. What prevents a molecule of ATP from breaking down until its energy is needed? Molecules can break down spontaneously; that is why ATP energy is needed to repair them. Fortunately for living things, it takes some additional energy, called energy of 30 , to get a chemical reaction started. This creates an energy 31 that prevents molecules from breaking down spontaneously. Energy barriers exist for both exergonic and endergonic reactions. Most of the time, most molecules in a cell lack the extra energy needed to clear the barrier, so chemical reactions occur slowly, if at all. So what enables the vital reactions of metabolism to occur when and where they are needed, at a rate sufficient to sustain life? This is where enzymes come in. An enzyme is a special 32 molecule that acts as a biological 33 It 34 the rate of a chemical reaction without being 35 by it. An enzyme holds reactants in such a way as to 36 the energy barrier that prevents them from reacting. Even though reactants would not normally pos- sess the activation energy needed to start the reaction, the enzyme creates conditions that make the reaction possible. Enzymes enable the cell to carry out vital chemical changes when and where they are needed, enabling it to control the many chemical reactions that make up cellular 37 Exercise 6 (Modules 5.10—5.14) Briefly summarize the differences between the words or phrases in each of the following sets. 1. Kinetic energy and potential energy 56 Chapter 5 2. Exergonic reactions and endergonic reactions 3. Reactants and products 4. ATPandADP 5. A reaction without an enzyme and a reaction with an enzyme 6. Photosynthesis and cellular respiration 7. First and second laws of thermodynamics 8. Mechanical, transport, and chemical work Exercise 7 (Modules 5.15-5.16) Review enzyme action by completing the activities below. 1. Complete the diagram below so that it shows the cycle of enzyme activity. Imagine that the reaction car- ried out by thisenzyme is splitting a substrate molecule into two parts. Color the diagram as suggested, and label the items in boldface type. Color the enzyme purple. Sketch the substrate as a dark green shape. Sketch the products, and color them light green. Also label the active site.  The Working Cell 57 2. Make a sketch showing how heat or change in pH might change the enzyme and alter its ability to cat- alyze its chemical reaction. Color and label the enzyme, its active site, and its substrate, as above. 3. On the left side of the space below, make a sketch showing how a competitive inhibitor might interfere with activity of the enzyme. Label the competitive inhibitor, and color it blue. On the right side, make a sketch showing how a noncompetitive inhibitor might interfere with activity of the enzyme. Label the noncompetitive inhibitor, and color it yellow. Test Your Knowledge 4. In osmosis, water always moves toward the solution, that is, toward the solution with the solute concentration. Multiple Choice a. isotonic... greater 1. The movement of molecules from an area of b. hypertonic... greater higher concentration to an area of lower con- c. hypertonic... lesser centration is called d. hypotonic... greater a. diffusion. e. hypotonic... lesser b. endocytosis. 5. Which of the following enables a cell to pick up c. catalysis. and concentrate a ppecific kind of molecule? d. active transport. a. passive transport e. osmosis. b. diffusion 2. Which of the following is not of an en- c. osmosis zyme? An enzyme d. receptor-mediated endocytosis a. is a protein. e. pinocytosis b. acts as a biological catalyst. c. supplies energy to start a chemical reaction. 6. A cell uses energy released by reactions to drive the reaction that makes ATP. Then it d. is specific. uses the energy released by the hydrolysis of e. lowers the energy barrier for a chemical re- ATP, an reaction, to do various kinds of action. work in the cell. 3. Phospholipid molecules in a membrane are a. exergonic... exergonic... endergonic arranged with their on the exterior and b. endergonic... exergonic... endergonic their on the interior. c. exergonic... endergonic... exergonic a. hydrophobic heads... hydrophilic tails d. endergonic... endergonic... exergonic b. hydrophilic heads... hydrophobic tails e. exergonic... endergonic... endergonic c. nonpolar heads... polar tails d. hydrophobic tails... hydrophilic heads e. hydrophilic tails... hydrophobic heads 58 Chapter 5 7. Energy of activation 2. Make a sketch showing why an enzyme acts a. is released when a large molecule breaks up. only on a specific substrate. b. gets a reaction going. 3. Most enzyme-catalyzed chemical reactions in c. is released by an exergonic reaction. humans occur most readily around body tem- d. is stored in an endergonic reaction. perature, 37 oc. Why do these reactions slow e. is supplied by an enzyme. down at lower temperatures? Why do they 8. The laws of thermodynamics state that when- slow down at higher temperatures? ever energy changes occur, always 4. Which contains more potential energy, a large, increases. complex molecule like a protein, or the smaller a. disorder amino acid subunits of which it is composed? b. order Is the joining of amino acids to form a protein c. energy an exergonic or endergonic reaction? Why d. potential energy must this be the case? Where does the cell ob- e. energy of activation tain energy to carry out such reactions? 9. Living things transform kinetic energy into po- tential chemical energy in the , when 5. Describe the circumstances under which plant ismade. and animal cells gain and lose water by osmo- a. mitochondrion ADP... sis.Which of the following is the least serious b. chloroplast... ADP problem: water gain by a plant cell, water loss c. chloroplast... an enzyme by a plant cell, water gain by an animal cell, or d. mitochondrion... glucose water loss by an animal cell? Why? e. chloroplast... glucose 10. Why does heating interfere with the activity of Apply the Concepts an enzyme? a. It kills the enzyme. Multiple Choice b. It changes the enzyme's shape. 1. If a cell is like a factory, then enzymes are like c. It increases the energy of substate molecules. a. the plans for the factory. d. It causes the enzyme to break up. b. the machines in the factory. e. It kills the cell, so enzymes can't work. c. the power plant for the factory. 11. An enzyme is specific. This means d. the raw materials used by the factory. a. it has a certain amino acid sequence. e. the walls of the factory. b. it found only in a certain place. is 2. A molecule that has the same shape as the sub- c. it functions only tmder certain environmen- strate of an enzyme would tend to tal conditions. a. speed metabolism by guiding the enzyme to d. it speeds up a particular chemical reaction. its substrate. e. it occurs in only one type of cell. b. speed metabolism by acting as a cofactor for 12. Diffusion of water across a selectively perme- the enzyme. able membrane is called c. speed metabolism because it would also be a a. acåve transport. catalyst. b. osmosis. d. save the cell energy by substituting for the c. exocytosis. substrate. d. passive transport. e. slow metabolism by blocking the enzyme's e. facilitated diffusion. active site. Essay 1. Describe the kinds of molecules that cannot eas- ily diffuse through cell membranes. How do proteins facilitate diffusion of these substances?  The Working Cell 59 3. A plant cell is placed in a solution whose solute 7. A nursing infant is able to obtain disease-fight- concentration is twice as great as the concentra- ing antibodies, which are large protein mole- tion of the cell cytoplasm. The cell membrane is cules,from its mother's milk. These molecules selectively permeable, allowing water but not probably enter the cells lining the baby's diges- the solutes to pass through. What will happen tive tract via to the cell? a. osmosis. a. No change will occur because it is a plant b. passive transport. cell. c. exocytosis. b. The cell will shrivel because of osmosis. d. active transport. c. The cell will swell because of osmosis. e. endocytosis. d. The cell will shrivel because of active trans- 8. Some enzymes involved in the hydrolysis port of water. of ATP cannot function without the help of e. The cell will swell because of active trans- sodium ions. Sodium in this case funcåons as port of water. a. a substrate. 4. A white blood cell is capable of producing and b. a cofactor. releasing thousands of antibody molecules c. an active site. every second. Antibodies are large, complex d. a noncompetitive inhibitor. protein molecules. How would you expect e. a vitamin. them to leave the cell? a. active transport 9. The relationship between an enzyme's active site and its substrate is most like which of the b. exocytosis following? c. receptor-mediated endocytosis a. a battery and a flashlight d. passive transport b. a car and a driver e. pinocytosis c. a key and a lock 5. Which of the following would be least likely to d. a glove and a hand diffuse through a cell membrane without the e. a hammer and nail help of a transport protein? a. a large polar molecule 10. In which of the following do both examples il- lustrate kinetic energy? b. a large nonpolar molecule a. positions of electrons in an atom—a ball c. a small polar molecule d. a small nonpolar molecule rolling down a e. Any of the above would easily diffuse b. heat—arrangement of atoms in a molecule c. a rock resting on the edge of a cliff—heat through the membrane. d. a ball rolling down a hill—heat 6. Red blood cells shrivel when placed in a 10% e. light—arrangement of atoms in a molecule sucrose solution. When first placed in the solu- tion, the solute concentration of the cells is 11. Which of the following is a difference between ac- the concentration of the sucrose solution. After five transport (AT) and facilitated diffusion (FD)? the cells shrivel, their solute concentration a. AT involves transport proteins, and FD does is the concentration of the sucrose not. solution. b. FD can move solutes against a concentration a. less than... greater than gradient, and AT cannot. b. greater than... less than c. FD requires energy from ATP, and AT does c. equal to... equal to not. d. less than... equal to d. FD involves transport proteins, and AT does e. greater than... equal to not. e. AT requires energy from ATP, and FD does not. 60 Chapter 5 12. An enzyme and a membrane receptor molecule 3. The laws of thermodynamics have imaginatively are similar in that they been described as the house rules of a cosmic en- a. are always attached to membranes. ergy card game: "You can't win, you can't break b. act as catalysts. even, and you want to stay alive) you can't (if c. require ATP to function. get out of the game." State thelaw that says liv- d. supply energy for the cell. ing things can't win the energy game. State the e. bind to molecules of a particular shape. law that says they can't break even. 13. discovered that the blood cells of a cer- 4. A farm worker accidentally was splashed with tain African lungfish were much slower to swell a powerful insecticide. A few minutes later he or shrink with water when faced with changes in went into convulsions, stopped breathing, and blood solute concenfraåon, a useful adaptation to died. The insecticide acted as a competitive in- drought and dehydration. eme researchers sus- hibitor of an enzyme important in the function pected ffut this might have something to do with of the nervous system. Describe the structural the number of in the blood cells relationship between the enzyme, its substrate, a. phospholipids and the insecticide. b. aquaporins c. ATPs 5. is a substance used in foods such as Lecithin d. competitive inhibitors mayonnaise as an emulsifier, which means that e. enzymes it helps oil and water mix. Lecithin is a phos- pholipid; a lecithin molecule has a polar (hy- Essay drophilic) "head" and a nonpolar 1. The burning of glucose molecules in paper is (hydrophobic) "tail." How might the structure an exergonic reaction, which releases heat and of lecithin allow water to surround fat light. If this reaction is exergonic, why doesn't droplets? Sketch a microscopic view of some the book in your hands spontaneously burst fat droplets in mayonnaise, and show how you into flame? You could start the reaction if you think the fat, surrounding water, and lecithin touched this page with a burning match. What molecules might be arranged. is the role of the energy supplied by the match? 2. Seawater is hypertonic in comparison to body tissues. Explain what would happen to his stomach cells if a shipwrecked sailor drank seawater. Put Words to Work Correctly use as many of the following words as possible when reading, talking, and writ- ing about biology: active site, active transport, aquaporin, cellular respiration, chemical energy, competitive inhibitor, concentration gradient, diffusion, endergonic reaction, endocytosis, energy, energy coupling, energy of activation (EA), entropy, enzyme, exergonic reaction, exocytosis, facilitated diffusion, feedback inhibition, first law of thermodynamics, fluid mosaic, hypertonic solution, hypotonic solution, isotonic solution, kinetic energy, metabolic pathway, metabolism, noncompetitive inhibitor, osmosis, osmoregulation, passive transport, phagocytosis, phosphorylation, pinocytosis, potential energy, second law of thermodynamics, selective permeability, substrate Use the Web There is more on membranes, energy, and enzymes at www.mybiology.com.