Reading Essentials for Biology Glencoe (794133), страница 17
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Draw a line from each term in Column A to the best explanation of the term in Column B.Column B1. compounda. substance with a pH of 72. elementb. an organism’s metabolism3. covalent bondc. forms hydroxide ions in water4. chemical reactionsd. forms hydrogen ions in water5. mixture6. solutione.
what holds hydrogen and oxygen togetherin a water molecule7. acidf. drink mix dissolved in water8. neutralg. sugar and sand stirred in a bowl9. baseh. what holds sodium and chloride togetherin table salt10. ionic bondi. goldj. table saltVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about atoms and their interactions.60Chapter 6READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Column ANameDateClassSection6.2 Water and Diffusion◗ Before You ReadThis section tells about the importance of water in our bodies and in other living organisms. Howimportant is water in your life? Could you go a day without using water? On the lines below, list theways water is important in your life.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnWater and Its ImportanceWhen was the last time you had a drink of water? Water is perhaps the most important compound in living organisms.
In fact,water makes up 70 to 95 percent of most organisms.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are the facts about water?You learned in the last section that when two atoms shareelectrons, the force that holds them together is called a covalentbond. This group of atoms held together by a covalent bondforms a molecule. Some molecules do not share the electronsequally. They form a polar bond.
A molecule with a polar bond iscalled a polar molecule.Hydrogen atomA polar molecule has aA In a covalentpositive end and a negabond betweenhydrogen andtive end. For example, theoxygen, theelectrons in a water molepⴙelectrons spendmore time nearcule spend more time nearthe oxygenthe oxygen nucleus thannucleus than nearthey do near the hydrogenthe hydrogennucleus.nuclei. This makes water8p ⴙa polar molecule. Part A8n 0of the figure to the rightshows a water molecule.Part B of the figure showsthat a water molecule is apolar molecule.Oxygen atomREADING ESSENTIALSIdentify the Main PointSkim the section and highlight the main idea of eachparagraph.ⴙPositivelycharged endⴙⴚNegativelycharged endpⴙHydrogen atomB Since oxygenattracts the electronsmore than hydrogendoes, the oxygenend of a watermolecule is slightlynegative and thehydrogen end isslightly negative.Chapter 661NameDateClassSection6.2Water and Diffusion, continued1. What allows water to dissolve salt and sugar?________________________________________________________________________Polar water molecules attract ions.
You learned in the last section that ions are positively and negatively charged atoms. Becauseof this attraction, water can dissolve many ionic compoundssuch as salt. It also can dissolve many other polar molecules suchas sugar.Water molecules also attract other water molecules. The positively charged hydrogen atoms of one water molecule attract thenegatively charged oxygen atoms of another water molecule.When water molecules bond with other water molecules, theyform a weak bond called a hydrogen bond. Hydrogen bonds areimportant because they hold molecules, such as proteins, together.Because water is a polar molecule, it is able to creep up thintubes, such as those found in plants. This allows plants to getwater from the ground.Water has a number of other special characteristics.
Waterresists temperature changes. It takes more heat to raise the temperature of water than it does to raise the temperature of mostother liquids. Water also loses a lot of heat when it cools. Waterexpands when it freezes. As a result, ice is less dense than liquidwater. This is why ice floats when it forms in water.Atoms and molecules of gases, liquids, and some solids moverandomly. The molecules, or particles, have energy of motion.They constantly move in straight lines until they collide withother particles.
When one particle hits into another particle, bothrebound off each other and move in different directions.Diffusion happens when particles move from an area of higherconcentration to an area of lower concentration. Diffusion resultsbecause of the random movement of particles. An area of higherconcentration has more particles in it than an area of lower concentration. Think of concentrated orange juice. If placed in acontainer of water, which has a lower concentration of orangejuice particles, the orange juice will begin to spread into the watereven if you do not mix it. This is diffusion. Diffusion is a slowprocess because it depends on the random movement of particles.62Chapter 6READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.DiffusionNameDateClassSection6.2Water and Diffusion, continuedWhat affects the speed of diffusion?There are three factors that affect how quickly particles diffuse:concentration, temperature, and pressure.
Concentration is themain factor in controlling the speed of diffusion. The more concentrated a substance, the more quickly it diffuses. When thereare more randomly moving particles, there are more collisionsamong them. More collisions increase the chance that the particles will bump each other into areas where no other particlesexist. If temperature increases, the particles’ motion speeds up(think of boiling water).
This speeds up the diffusion process.Increasing pressure will also speed up particle motion. This, too,speeds up diffusion.2. Apply Which will diffusemore quickly? (Circle yourchoice.)a. concentrated orangejuice in cold waterb. concentrated orangejuice in warm waterCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Result of Diffusion Diffusion is complete when all the particlesin a mixture become evenly distributed or mixed. At this point,the particles are still moving, but the concentration of the particles will not change.
This is called dynamic equilibrium. Thefigure below shows how diffusion occurs. The last illustration inthe figure shows dynamic equilibrium.CellCellCellWater moleculeWater moleculeWater moleculeDiffusion in Living Systems Diffusion is one of the ways cellsmove substances in and out of the cell. This is also illustrated inthe figure above. Notice in the first illustration that the concentration is higher outside the cell. In the second illustration, theconcentration level in the cell is increasing. In the last illustration,the concentration level is equal on the inside and outside of thecell. In other words, there is dynamic equilibrium.READING ESSENTIALS3. Why do cells use diffusion?________________________________________________Chapter 663NameDateClassSection6.2Water and Diffusion, continued◗ After You ReadMini Glossarydiffusion: random movement of particles froman area of higher concentration to an areaof lower concentrationhydrogen bond: weak chemical bond formed bythe attraction of positively charged hydrogenatoms to other negatively charged atomsdynamic equilibrium: result of diffusion wherethere is continuous movement of particlesbut no overall change in concentrationpolar molecule: molecule with an unequal distribution of charge, resulting in the moleculehaving a positive end and a negative end1.
Review the terms and their definitions in the Mini Glossary above. Select one term andwrite a definition of it in your own words.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2.
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