MHE_Rdg_Wonders_LvRdr_G5_Beyond_U5W3_23.pdf

Expository TextThreatsOceanby Ken BennPAIREDREAD Floating TrashProgram:CR 14Component:LRG5 U5 W3 B PDFVendor:Learning MediaLevel:60CV_CR14_LR_G5_U5W3L60_B_119096.indd 2CV_CR14_LR_G5_U5W3L60_B_119096.indd 26/03/12 3:33 PM6/03/12 3:33 PMSTRATEGIES&SKILLSPhotography Credit:Digital Vision/Getty Images*The total word count is based on words in the running text and headings only.Numerals and words in captions,labels,diagrams,charts,and sidebars are not included.AWord Count:2,394*ComprehensionStrategy:Ask and Answer QuestionsSkill:Compare and ContrastVocabulary StrategyParagraph CluesVocabularyatmosphere,decay,gradual,impact,noticeably,receding,stability,variationsContent StandardsScienceEarth and Space ScienceProgram:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Copyright The McGraw-Hill Companies,Inc.All rights reserved.No part of this publication may be reproduced or distributed in any form or by any means,or stored in a database or retrieval system,without the prior written consent of The McGraw-Hill Companies,Inc.,including,but not limited to,network storage or transmission,or broadcast for distance learning.Send all inquiries to:McGraw-Hill EducationTwo Penn PlazaNew York,New York 10121ISBN:978-0-02-119096-6MHID:0-02-119096-8Printed in the United States.1 2 3 4 5 6 7 8 9 DOC 15 14 13 12 11 10IFCIBC_CR14_LR_G5_U5W3L60_B_119096.indd 2IFCIBC_CR14_LR_G5_U5W3L60_B_119096.indd 212/03/12 10:52 AM12/03/12 10:52 AMPAIREDREADIntroduction .2Chapter 1What Are Algae?.4Chapter 2What Causes Algal Blooms?.8Chapter 3Why Should We Be Concerned?.12Conclusion.16Respond to Reading.18Floating Trash.19Glossary.22Index.23Focus on Science .24by Ken BennThreatsOcean Essential QuestionWhat changes in the environment affect living things?Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60001_009_CR14_LR_G5_U5W3L60_B_119096.indd 1001_009_CR14_LR_G5_U5W3L60_B_119096.indd 16/03/12 3:37 PM6/03/12 3:37 PMIntroductionDid you know that nearly three-quarters of our planet is covered in water?Earth s rivers,lakes,and oceans support many living organisms.Algae are some of the most widespread of aquatic life forms.Although most algae need moisture,some even live in desert sand.Algae are simple plant-like organisms,and there are thousands of different species.Scientists classify them into different groups according to color,structure,and habitat.The smallest species of algae are tiny plankton just 0.00004 of an inch long,while the largest species grows up to 200 feet long.Many algae are harmless,and in fact,algae play a very important part in ecology.However,scientists have identified around 100 species of algae as toxic.They can threaten animal and human health.Large populations of algae may even create areas in the ocean where nothing else can live.2Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Don Johnston/age fotostock/Getty Images001_009_CR14_LR_G5_U5W3L60_B_119096.indd 2001_009_CR14_LR_G5_U5W3L60_B_119096.indd 26/03/12 3:37 PM6/03/12 3:37 PMAlgal blooms can cover many miles,threatening life all along a coastline.Like all living organisms,algae need a favorable environment in which to survive.However,highly favorable conditions can create algal population explosions,called“algal blooms.”Algal blooms have occurred throughout history.Some people believe that the Red Sea is named after the red color of some algal blooms.In many parts of the world,algal blooms are a seasonal occurrence.However,these blooms are happening more frequently and in more places.They also last longer and are noticeably bigger.Some scientists warn that the impact of algal blooms on the ecology of our oceans,lakes,and rivers could be far more serious than we realize.3Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60EyePress News EyePress/Newscom001_009_CR14_LR_G5_U5W3L60_B_119096.indd 3001_009_CR14_LR_G5_U5W3L60_B_119096.indd 36/03/12 3:37 PM6/03/12 3:37 PMAlgae have been around for a very long time.Many scientists believe fossil evidence shows algae have been present on Earth for nearly 2 billion years.Most algae live in aquatic environments,such as oceans,lakes,rivers,streams,and ponds.Some algae live on land,but most of these prefer damp conditions,such as on tree trunks or brickwork.Algae can adapt to extremessome kinds live in snow and ice,others in hot springs.Some species of algae are even found on animals,including turtles and three-toed sloths!Like plants,algae can have a simple or complex structure.Microscopic,one-celled algae are called microalgae.They include phytoplankton in the ocean.Multi-celled algae are called macroalgae.Seaweeds are macroalgae.The largest,kelp,can grow up to 200 feet long.Although seaweeds might look plant-like,algae are not true plants.They lack roots,stems,and leaves.What Are Algae?p ypMulti-celled amacroalgae.Seaweeds aThe largest,keup to 200 feet seaweeds mighalgae are not tThey lack rootleaves.lChapter 1These freshwater colonial green algae are very small.You need a microscope to see them.4Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Stephen Durr 001_009_CR14_LR_G5_U5W3L60_B_119096.indd 4001_009_CR14_LR_G5_U5W3L60_B_119096.indd 46/03/12 3:37 PM6/03/12 3:37 PMAlgae are very simple life forms,yet they play a vital role in the ecology of our planet.They are an important part of the food web.Like plants,algae are called primary producers because other organisms in the food web eat them,but algae don t eat other living things.Plants and algae both use a process called photosynthesis.The word photosynthesis comes from Greek,and means“putting together through light.”Through photosynthesis,algae and plants use the sun s energy to make food from carbon dioxide and water.Plants and algae both release oxygen as part of this process.Plants produce most of the oxygen that humans need to breathe.Almost all forms of marine life,both plant and animal,depend on algae for their oxygen.This red algae and the sponge both benefit from their symbiotic relationship.Some algae live in a“win-win”relationship with other organisms.Relationships such as these,where both organisms benefit,are called symbiotic.For example,various species of algae grow inside other organisms,such as sponges or corals.These larger organisms get oxygen and nutrients from the algae.In return,the algae get a good place to hide from hungry predators.A“Win-win”Relationship 5Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Jeffrey L.Rotman/CORBIS001_009_CR14_LR_G5_U5W3L60_B_119096.indd 5001_009_CR14_LR_G5_U5W3L60_B_119096.indd 56/03/12 3:37 PM6/03/12 3:37 PM Although algae are present in most aquatic environments,we don t always notice them.When there is stability in an ecosystem,species are in balance.However,under some conditions,algae populations increase rapidly.Warmer water temperatures or higher levels of carbon dioxide can both lead to algal blooms.Large blooms can noticeably change the appearance of the water.Blooms occur in both freshwater and in oceans.Blue-green algae often form freshwater algal blooms in summer.In tropical places,the blooms may last all year.Marine algal blooms often look red,but may also be green,yellow,or brown.A Al lth hough h al lgae w we e d do on n t t a al lw wa ay ys s n no ot tecosystem,species c co on nd di it ti io on ns s,a al lg ga ae e p po otemperatures or higlead to alg gal bloomsappearance of the wBlooms occur inalgae often form freI In n t tr ro op pi ic ca al l p pl la ac ce eblooms often look rIn 2010,an algal bloom,or“green tide,”covered 7,700 square miles of the Yellow Sea,off the eastern coast of China.It was a serious health hazard to the people who lived there.6Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60STR/AFP/Getty Images001_009_CR14_LR_G5_U5W3L60_B_119096.indd 6001_009_CR14_LR_G5_U5W3L60_B_119096.indd 66/03/12 3:37 PM6/03/12 3:37 PMSome types of algae can look like thick sludge floating on the surface,while other kinds can look like foam.There are many parts of the world where blooms happen regularly,such as the coast of Florida and the Red Sea.These regular blooms last for a month or two before receding.However,unusual variations in the environment can cause abnormally large blooms to take place.Such blooms can affect vast areas of ocean and are even visible from satellites in space.These“super blooms”may last for many months.One such super bloom occurred in the Antarctic in February 2011,and others occurred off the coast of China and in the Baltic Sea in 2010.This photo of an algal bloom off the coast of Florida was taken by a satellite.Red Sea.These e receding.nment can cause blooms can affect satellites in space.nths.One such ruary 2011,and the Baltic Sea algal bloom7Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Jacques Descloitres,NASA Photo by Universal History Archive/Getty Images 001_009_CR14_LR_G5_U5W3L60_B_119096.indd 7001_009_CR14_LR_G5_U5W3L60_B_119096.indd 76/03/12 3:37 PM6/03/12 3:37 PMAlgae need nutrients,carbon dioxide,water,and sunlight to grow.Algae respond to changes in the availability of any of these elements.Such changes can sometimes be sudden rather than gradual and can result in rapid increases or decreases in algae populations.Many algal blooms occur naturally.Seasonal changes to ocean currents can cause nutrient-rich water from deep in the ocean to rise to the surface.With more nutrients,algae multiply.For example,the Loop Current carries deep ocean water into the Gulf of Mexico.This leads to regular blooms off the west coast of Florida.Increased carbon dioxide(CO2)can also trigger blooms.Scientists estimate that the ocean contains up to 50 times more CO2 than what the atmosphere holds.The ocean soaks up and stores gases like a sponge,so if there is an excess of CO2 in the atmosphere,much of it will be absorbed by the ocean.What Causes Algal Blooms?Chapter 28Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60001_009_CR14_LR_G5_U5W3L60_B_119096.indd 8001_009_CR14_LR_G5_U5W3L60_B_119096.indd 86/03/12 3:37 PM6/03/12 3:37 PMSome natural events,such as volcanic eruptions,release CO2 into the atmosphere.There is also a lot of volcanic activity in the ocean.Undersea volcanoes are still being found.A 2011 survey discovered a chain of active volcanoes,some as large as Mount Fuji,off the coast of Antarctica.Volcanoes such as these pump CO2 into the ocean.Just as the ocean absorbs CO2,it also absorbs heat.Scientists believe that oceans absorb 20 times more heat than the atmosphere does.In warm water,algae multiply faster than they do in cold water.Bright sunshine and warm weather also contribute to algal blooms.The atmospheric temperature is changing all the time.There are many natural influences on the global temperature.Earth receives its energy from the sun.Sun storms,or solar flares,can deliver unusually large amounts of energy,or heat,to Earth.When undersea volcanoes erupt,they release CO2 into the ocean.They may also release CO2 into the atmosphere.9Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Dana Stephenson/Stringer/Getty Images001_009_CR14_LR_G5_U5W3L60_B_119096.indd 9001_009_CR14_LR_G5_U5W3L60_B_119096.indd 96/03/12 3:37 PM6/03/12 3:37 PMMany countries are introducing stricter controls to reduce the air pollution caused by industry.Many scientists believe human activity has lead to wide-scale environmental change,including the increase in algal blooms.Evidence suggests that CO2 levels in the atmosphere have risen noticeably over the last 100 years.This rise can be traced back to the industrial revolution of the 1800s,when large-scale burning of fossil fuels started.As the world s population has increased,so has fossil fuel consumption.Fossil fuels,such as oil,coal,and natural gas,are used for:motorized transportation factories and industry power plants to generate electricity.Human use of land,particularly forest clearance,also increases CO2 in the atmosphere.This is because plants and trees absorb CO2 during photosynthesis.10Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60James Jordan Photography/Flickr/Getty Images010_018_CR14_LR_G5_U5W3L60_B_119096.indd 10010_018_CR14_LR_G5_U5W3L60_B_119096.indd 106/03/12 3:41 PM6/03/12 3:41 PMWhat Is the Greenhouse Effect?Earth receives almost all of its energy from the sun.Energy must be released back into space from Earth,or the planet could become hotter and hotter.Greenhouse gases such as CO2 and water vapor block some energy from radiating back out into space.They trap heat in Earths lower atmosphere,and Earths surface becomes warmer.This result of climate change is known as global warming.When atmospheric temperatures rise,weather systems become more extreme.This can lead to flooding.Also,the soil from heavily fertilized farmland can empty into waterways.The soil can contain elements such as nitrogen and phosphorus,which many farmers rely on to increase their crops.Such elements are also nutrients that help algae grow.During floods,sewers may also overflow.Human and animal waste contains nutrients.Erosion also contributes to nutrient runoff.An increase in nutrients creates ideal conditions for algal blooms to form.The Greenhouse Effect some energy reflected back to spacesome energy reflected back to Earthgreenhouse gases in atmospheresome energy reaches Earthsome energy escapes11Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60Illustration:Carlos Aon010_018_CR14_LR_G5_U5W3L60_B_119096.indd 11010_018_CR14_LR_G5_U5W3L60_B_119096.indd 116/03/12 3:41 PM6/03/12 3:41 PMWhy Should We Be Concerned?Chapter 3Health Ri sks Some algal blooms are harmless to humans and do no more than discolor the water.At worst they can affect tourism to coastal areas.However,there are around 100 toxic species of algae,and when these toxic algae invade seafood,particularly shellfish such as oysters,clams,scallops,and mussels,they enter the food web.People who then eat this seafood can suffer anything from mild dizziness or headaches to severe vomiting,paralyzed muscles,and even death.A satellite recorded this dust storm blowing off the coast of northern Africa in 2005.12Program:CR 14Component:LRG5 U5 W3 BPDFVendor:Learning MediaLevel:60NASA image by Jeff Schmaltz,MODIS Rapid Response Team,Goddard Space Flight Center010_018_CR14_LR_G5_U5W3L60_B_119096.indd 12010_018_CR14_LR_G5_U5W3L60_B_119096.indd 126/03/12 3:41 PM6/03/12 3:41 PMSome algae are also toxic to wildlife.Algae thrive on iron.Dust storms in the Moroccan desert dump large amounts of iron into the sea.This encourages the growth of algae and a dangerous type of ocean bacteria,Vibrio,that can trigger diseases such as cholera.The health risks from harmful algal blooms are not restricted to eating fish or shellfish.People who swim near blooms or breathe in contaminated air can also suffer ill effects.These include eye,nose,and throat irritation.One kind of airborne toxin causes asthma-like breathing problems.Now scie