Reading Essentials for Biology Glencoe (794133), страница 68
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Because of this,land animals need to use more oxygen and energy to find food.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.IdentifyDetails As you read this section, highlight the sentencesthat provide informationabout sessile organisms.All animals have several characteristics in common.
Animals areeukaryotic, multicellular organisms. They have ways of movingthat help them reproduce, get food, and protect themselves. Mostanimals have specialized cells. These cells form tissues andorgans, such as nerves and muscles.NameDateClassSection25.1Typical Animal Characteristics, continuedHow do animals digest food?Animals are heterotrophs that ingest, or take in, their food.After they ingest it, they must digest it. In some animals, digestion takes place within individual cells. In other animals, digestiontakes place in an internal cavity. Some of the food that an animalingests and digests is stored as fat or glycogen, which will be usedwhen other food is not available.MouthExtendedpharynxB EarthwormDigestive tractMouthDigestivetractAnusCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.A Flatworm (planarium)Examine the digestive tracts of a flatworm (planarium) and anearthworm in the illustration above.
You will notice that there isonly one opening to the flatworm’s digestive tract, a pharynx. Theearthworm has a digestive tract with two openings. There is amouth at one end and an anus at the other.What are the functions of some animal cells?Most animal cells carry out different functions. Animals havespecialized cells that allow them to sense and find food and mates.They also have specialized cells that help them to identify andprotect themselves from predators.Development of AnimalsMost animals develop from a fertilized egg cell called a zygote.How does a zygote develop into the many different kinds of cellsthat make up a snail, a fish, or a human? After fertilization, thezygotes of different animal species all have similar, geneticallydetermined stages of development.READING ESSENTIALS2.
Analyze Why do landanimals use more energythan aquatic animals tofind food?________________________________________________3. Most animals developfrom a fertilized cellcalled a (Circle yourchoice.)a. sperm cell.b. haploid cell.c. zygote.Chapter 25297NameDateClassSection25.1Typical Animal Characteristics, continuedWhat happens during fertilization?Most animals reproduce sexually. Male animals produce spermcells and female animals produce egg cells.
Fertilization occurswhen a sperm cell penetrates an egg cell, forming a new cell calleda zygote. Fertilization may occur inside or outside of the body.How does cell division occur?4. Once cell division starts,what is the organismcalled?________________________________________________________________________The zygote divides by mitosis and cell division to form twocells. This process is called cleavage. Once cell division has started,the organism is called an embryo. Remember that an embryo isan organism at an early stage of growth and development.The two cells that result from cleavage then divide to formfour cells, and so on, until a cell-covered, fluid-filled ball called ablastula (BLAS chuh luh) is formed. The blastula is formed earlyin the development of an animal embryo.
In sea urchins, the blastula is formed within about 10 hours of fertilization. In humans,the blastula is formed about five days after fertilization.5. What do ectoderm cellsdevelop into?________________________________________________________________________After the blastula is formed, cell division continues. The cellson one side of the blastula move inward to form a gastrula(GAS truh luh). This is a structure made up of two layers ofcells with an opening at one end.The way the gastrula forms can be compared to the way a potter makes a bowl from a ball of clay.
By pushing in on one side ofthe clay ball, the potter forms a cavity that becomes the interiorof the bowl. Similarly, the cells at one end of the blastula moveinward, forming a cavity lined with a second layer of cells. Thelayer of cells on the outer surface of the gastrula is called theectoderm. The layer of cells lining the inner surface of the gastrula is called the endoderm.
The cells continue to grow anddivide. Eventually the ectoderm cells develop into the skin andnervous tissue of the animal. The endoderm cells develop into thelining of the digestive tract and into organs that aid digestion.How is the mesoderm formed?In some animals, the development of the gastrula progresses untila layer of cells called the mesoderm forms as shown in the illustration on page 299. Mesoderm is found in the middle of the embryo.The term “meso” means middle.The mesoderm (MEZ uh durm) is the third cell layer found inthe developing embryo between the ectoderm and the endoderm.The mesoderm cells develop into the muscles, circulatory system,298Chapter 25READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is gastrulation?NameDateClassSection25.1Typical Animal Characteristics, continuedSperm cellsEgg cellA FertilizationA zygote is formed.F Formation of mesodermEndodermB First cell divisionCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.The zygote divides bymitosis and cell divisionto form two cells.EctodermMesodermC Additional cell divisionsEGastrulationAs the embryo continues to grow,some of the cells of the blastulamove inward, forming the gastrula.D Formation of a blastulaexcretory system, and, in some animals, the respiratory system.When the opening in the gastrula develops into the mouth, theanimal is called a protostome (PROH tuh stohm).
Snails, earthworms, and insects are examples of protostomes.READING ESSENTIALSChapter 25299NameDateClassSection25.1Typical Animal Characteristics, continuedIn other animals, such as sea stars, fishes, toads, snakes, birds, andhumans, the mouth does not develop from the gastrula’s opening.When the mouth develops from cells on another part of the gastrula, the animal is called a deuterostome (DEW tihr uh stohm).Scientists hypothesize that protostome animals were the first toappear in evolutionary history, and that deuterostomes followedlater. Biologists today often classify an unknown organism byidentifying its phylogeny, the evolutionary history of an organism.Determining whether an animal is a protostome or deuterostomecan help biologists identify its group.6. Summarize What happens to most animalsonce the juvenile or larvalstage has passed?________________________________________________________________________Cells in developing embryos continue to differentiate, whichmeans they become specialized to perform certain functions.
Mostanimal embryos continue to develop over time. They becomejuveniles that look like smaller versions of the adult animal. Insome animals, such as insects and echinoderms, the embryo develops inside an egg into an intermediate stage called a larva (plural,larvae). A larva often does not look like the adult animal. Insidethe egg, the larva is surrounded by a membrane formed rightafter fertilization.When the egg hatches, the larva breaks thorough the membrane.
Animals that are generally sessile as adults, such as seaurchins, often have a free-swimming larval stage.Once the juvenile or larval stage has passed, most animals continue to grow and develop into adults. This growth and development may take only a few days in some insects. In some mammalsit can take up to fourteen years. Eventually the adult animalsreach sexual maturity, mate, and the cycle begins again.◗ After You ReadMini Glossaryblastula (BLAS chuh luh): a cell-covered, fluidfilled ball formed in the early developmentof an animal embryodeuterostome (DEW tihr uh stohm): animalwhose mouth develops from cells otherthan those at the opening of the gastrulaectoderm: layer of cells on the outer surface ofthe gastrula; eventually develops into theskin and nervous tissue of an animal300Chapter 25endoderm: layer of cells on the inner surface ofthe gastrula; will eventually develop intothe lining of the animal’s digestive tract andorgans associated with digestiongastrula (GAS truh luh): animal embryo development stage where cells on one side of theblastula move inward forming a cavity oftwo or three layers of cells with an openingat one endREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What changes occur during growth anddevelopment?NameDateClassSection25.1Typical Animal Characteristics, continuedmesoderm (MEZ uh durm): middle cell layer inthe gastrula, between the ectoderm and theendoderm; develops into the muscles, circulatory system, excretory system, and in someanimals, the respiratory systemprotostome (PROH tuh stohm): animal with amouth that develops from the opening inthe gastrulasessile (SE sul): organism that permanentlyattaches to a surface1.
Read the terms and definitions in the Mini Glossary. Circle the three terms that refer to thelayers of the gastrula. Then write the terms on the lines provided.__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2.
Write one phrase provided below in each division of the pyramid to show the stages ofanimal development. Be sure to list the stages in the correct order.Embryo formsBlastula formsMitosis occursZygote formsFertilizationoccursCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Cell division continuesCells form gastrulaVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about typical animal characteristics.READING ESSENTIALSChapter 25301NameDateClassSection25.2 Body Plans and AdaptationsSC.G.1.4.1 The student knows of the great diversity and interdependence of living things.◗ Before You ReadIn this section, you will learn about the arrangements of body structures in animals.
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