原版英语RAZ 教案(U) Life Cycles.pdf

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1、Visit www.readinga- for thousands of books and materials.Life CyclesA Reading AZ Level U Leveled BookWord Count:1,154www.readinga-LEVELED BOOK UWritten by Robert CharlesIllustrated by Signe NordinLife CyclesLife Cycleswww.readinga-Written by Robert CharlesIllustrated by Signe NordinLife CyclesLife C

2、yclesLife CyclesLevel U Leveled Book Learning AZWritten by Robert CharlesIllustrated by Signe NordinAll rights reserved.www.readinga-Photo Credits:Front cover,pages 4(bottom inset),7:C Squared Studios/Photodisc/Getty Images;back cover,page 12:GeoStock/PhotoDisc/Getty Images;title page,pages 4(main),

3、11,18:Corbis;pages 4(top inset),15(main):Fabio Liverani/Nature Picture Library/Getty Images;page 5(all):Kevin Peterson/Photodisc/Getty Images;page 6:Exactostock/SuperStock;page 8:Nicola Sutton/Life File/PhotoDisc/Getty Images;page 9:PhotoDisc;page 13:Cathy Keifer/D;page 14:Don Johnston/All Canada Ph

4、otos/SuperStock;page 15(inset):PhotoDisc;page 16:Steve Bloom Images/SuperStockCorrelationLEVEL UQ4040Fountas&PinnellReading RecoveryDRA3Table of ContentsIntroduction .4Human Life Cycle .6Animal Life Cycles .12Plant Life Cycles .17Glossary .20Life Cycles Level U4IntroductionWhether plant or animal,al

5、l living things undergo changes as they go through life.This is also true for tiny living things made of only one cell.This book is about the changes living things go through during their lifetime.It is about life cycles.5A life cycle includes all the stages a living thing goes through from birth to

6、 death.All living things have a beginning,and they all must die.What happens between birth and death varies from one kind of living thing to another.Most living things have one thing in commonthey begin life as a tiny single cell.The simplest forms of life never grow beyond a single cell.The life cy

7、cle of these simple life forms is really just a matter of growing a bit larger and then dividing into two smaller cells.But most of the plants and animals we know have much more complicated life cycles.We are going to examine how life cycles differ among some plants and animals.Life Cycles Level U6H

8、uman Life CycleLets start with you.You are a human being,or at least I hope you are.You started out as a tiny egg inside your mother,and you began to change when that tiny egg began to split.It split and split and split and continued splitting until it split millions and millions of times.Before lon

9、g,body parts began to form.You began to get legs,arms,a head,and a whole bunch of organs,and over time,you looked more and more like a human.7After about nine months of cell splitting and development inside your mother,you were born.You entered the first stage of life as an infant.You were pretty he

10、lpless at first,but you continued to grow and get stronger.Life Cycles Level U8In the next stage of your life cycle,you became a toddler.Thats when you got into lots of trouble.You learned to walk and talk,and you probably got into all sorts of things.You probably also said some things you should no

11、t have said.Then you entered childhood.This is where you are now and where you will stay for a few more years.During childhood,you learn more and more about taking care of yourself.You will become less dependent on your parents by learning how to do all sorts of things,from riding a bike to reading

12、and writing.As a child,you can now feed yourself,go to the bathroom by yourself,and dress yourself.9You will stay at this stage for several years until you enter adolescence.This is the stage when children rapidly grow into adulthood.This stage is also called your teen years.Life Cycles Level U10The

13、 adult stage is the longest,going on for many years.In fact,the average adult stage lasts more than fifty years,and adult life spans seem to get longer and longer.Toward the end of your adult stage,you will become what many people call a“senior citizen.”This is the last stage of the human life cycle

14、.11The adult stage is when many people choose to have and raise children.These children will also go through a life cycle and change with each stage.When an animal produces more of its own kind,it helps ensure that that kind of animal will remain on Earth.If a kind of animal dies off faster than it

15、can reproduce,it becomes extinct and disappears from Earth.Long ago,humans had to produce many offspring to make sure that we would survive.Now,however,the number of humans on Earth is too many for the balance of life on our planet.This is called overpopulation.Many countries around the world are wo

16、rking to limit the number of babies each family produces.Over time,this may help to restore the balance.Now lets look at some other life cycles.Life Cycles Level U12Animal Life CyclesEven small animals like insects go through life cycles.Most insects go through three or four stages during their life

17、 cycle.The change an insect goes through during its life is called metamorphosis.All insects begin as eggs.During the stage after the egg stage,known as the larval stage,many insects look much different than they do as adults.As a larva,many insects eat huge amounts of food.13They grow larger and th

18、en enter a stage where they are not active.For some insects,this stage is spent inside a protective covering called a cocoon.Other insects spend this stage inside a hard case called a chrysalis.When insects leave this stage,known as the pupa,they enter the adult stage of their life.As adults,female

19、and male insects mate.The female then lays eggs,and the life cycles of many new insects begin.A monarch butterfly emerging from a chrysalisDo You Know?An insect known as the mayfly has an adult life that is only one day long.Life Cycles Level U14Some animals lay eggs with shells as the first stage o

20、f their life cycle.Birds and reptiles lay eggs that are covered by protective shells.The eggs hatch when the baby animal breaks through the protective shell.The young animal that emerges has many of the same features as the adult.Other animals,like frogs and fish,lay eggs without shells in jellylike

21、 clumps.These eggs are usually laid in water.A snapping turtle hatchingDo You Know?Reptile eggshells are soft like leather.Bird eggshells are hard and brittle.15When a frog egg hatches,a creature called a tadpole emerges.The tadpole looks more like a fish than a frog.It slowly changes during its lif

22、e cycle,growing legs,developing lungs,and losing its tail.Soon it looks like a frog.Fish eggs,on the other hand,hatch into tiny fish,called fry,which more closely resemble adult fish.Do You Know?Some insects and frogs lay thousands of eggs in a lifetime.Some birds lay only one egg a year.Life Cycles

23、 Level U16Other animals give birth to live babies.Some of these babies are born helpless and blind.Rabbits,mice,and kittens are like this and require a lot of care from their mothers.Marsupials,or pouched animals,such as kangaroos,give birth to very tiny,helpless babies that they keep in a special p

24、ouch until the babies develop enough to survive outside the pouch.Other baby animals are born ready to walk and run.A newborn giraffe is six feet (2 meters)tall at birth and is able to walk.17Plant Life CyclesMost plants begin their life cycle as seeds.It is hard to imagine that a giant oak tree was

25、 once a small acorn.When it first sprouts,it is called a seedling,but over the years it grows larger and becomes a young tree called a sapling.After a few more years,it becomes an adult tree capable of making seeds(acorns)that will grow into new trees.Plants are not born,and they do not hatch.Instea

26、d,a seed germinates or sprouts to form a new plant.Life cycle of an oak treeseedseedlingsaplingadult treeLife Cycles Level U18Some plant life cycles last hundreds of years.A bristlecone pine can live well over a thousand years.Plants with life cycles that are several years long,such as trees,grass,a

27、nd shrubs are called perennials.Other plants,called annuals,live through only a single season.Many garden plants,including peas,beans,corn,and tomatoes,are annuals.Do You Know?The largest living thing is the giant sequoia tree.It grows from a tiny pinecone seed.19T R Y T H I SObserving a Plant Life

28、CycleMaterials:Clear plastic cup Dirt Bean seeds WaterSteps:1 Fill the cup with dirt.2 Place the seeds about one-half inch below the soil.3 Water the seeds enough to moisten the dirt.4 Water again when the dirt begins to get dry.5 Observe the growth.6 Keep a journal of the changes.Measure the height

29、 every three days.Make drawings of the different stages.Life Cycles Level U20Glossaryadult(n.)the mature stage of a living things life cycle(p.10)adolescence(n.)the stage of the human life cycle that comes just before adulthood(p.9)annuals(n.)plants having a one-year life cycle (p.18)extinct(adj.)no

30、 longer in existence;completely wiped out(p.11)fry(n.)the stage of the fish life cycle after the eggs hatch(p.15)germinates(v.)to begin to sprout from a seed(p.17)infant(n.)a human baby(p.7)larval stage(n.)the wormlike stage of an insects life cycle(p.12)life cycle(n.)the stages a living thing goes through during its lifetime(p.5)metamorphosis an animals change from one shape(n.)to a totally different shape(p.12)perennials(n.)plants that live many years(p.18)pupa(n.)an immature insect before the adult stage(p.13)sapling(n.)a young tree(p.17)seedling(n.)a young plant(p.17)