Reading Essentials for Biology Glencoe (794133), страница 77
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What are the advantagesof jointed appendages?________________________338Chapter 28Arthropods as a group have been successful partly because theyhave exoskeletons. The exoskeleton is made of protein and chitin(KI tun). In some species, the exoskeleton is a continuous coveringover most of the body. In other species, it is made of separateplates held together by hinges. The exoskeleton protects and supports internal tissue and provides a place for the attachment ofmuscles. In many species that live on land, a waxy layer on theexoskeleton protects against water loss.
In aquatic species, theexoskeleton may be reinforced with calcium carbonate.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is an arthropod?NameDateClassSection28.1Characteristics of Arthropods, continuedCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are the disadvantages of an exoskeleton?One disadvantage of an exoskeleton is that it is a relativelyheavy structure. The larger an arthropod is, the thicker and heavier its exoskeleton must be to support its larger muscles. Theweight of the exoskeleton limits the size of arthropods. Some landdwelling and flying arthropods have adapted by having thinner,lighter exoskeletons.
A thinner exoskeleton offers less protectionbut allows the animal to fly or jump.Another disadvantage is that the exoskeleton does not grow.An exoskeleton must be shed periodically. Shedding the oldexoskeleton is called molting. Before an arthropod molts, a new,soft exoskeleton forms under the old one. When the new exoskeleton is ready, the animal contracts muscles and takes in air orwater. This causes the animal’s body to swell. The old exoskeletonsplits open and the animal sheds it.
The new exoskeleton is soft.Before it hardens, the animal puffs up as a result of increasedblood circulation to all parts of the body. Many insects and spiders also increase in size by taking in air. The new exoskeletonhardens in a larger size, allowing some room for the animal tocontinue growing.Most arthropods molt four to seven times in their lives beforethey become adults. During molting, they are at risk from predators. While the new exoskeleton is soft, arthropods cannot protectthemselves from danger. Many species hide or remain motionlessfor a few hours or days until the new exoskeleton hardens.2. What limits the size ofarthropods?________________________________________________________________________3. What happens before ananimal molts?________________________________________________________________________How is fusion related to movement and protection?Most arthropods are segmented but they do not have as manysegments as worms.
In most groups of arthropods, segments havebecome fused into three body sections—head, thorax, and abdomen.In other groups, even these segments may be fused. Some arthropods have a head, but the thorax and abdomen are fused. Othershave a head fused with a thorax, and an abdomen. A fused headand thorax is called a cephalothorax (se fuh luh THOR aks).Fusion of the body segments is related to movement and protection.
Less fusion means more movement, but less protection.Beetles and some other arthropods that have separate head andthorax sections are more flexible than those with fused sections.Shrimps, lobsters, and crayfishes have a cephalothorax, whichprotects the animal but limits its movement.READING ESSENTIALS4. Name the three body sections of most arthropodgroups.________________________________________________________________________Chapter 28339NameDateClassSection28.1Characteristics of Arthropods, continuedA Tracheal tubes are inside the body, therebyreducing water loss through the respiratorysurface while carrying air close to each cell.B Gills, with their large surface area, enable alarge amount of blood-rich tissue to be exposedto water containing oxygen.Arthropods are quick, active animals.
Theycrawl, run, climb, dig, swim, and fly. In order tohave oxygen delivered quickly to the cells, theyneed efficient respiratory structures.Three types of respiratory structures haveevolved in arthropods: gills, tracheal tubes, andbook lungs. Aquatic arthropods use gills to getoxygen from the water and release carbon dioxideinto the water.
Land arthropods either have a system of tracheal tubes or book lungs. Most insectshave tracheal (TRAY kee ul) tubes, a network ofhollow air passages that carry air throughout thebody. Muscle activity helps pump the air throughthe tracheal tubes. Air enters and leaves the tracheal tubes through openings on the thorax andabdomen called spiracles (SPIHR ih kulz).Most spiders and their relatives have booklungs, air-filled chambers that contain leaflikeplates. The folded membranes increase the surfacearea of tissue exposed to air.
The stacked plates ofthe book lungs are arranged like pages in a book.What senses do arthropods have?C Book lungs are folded membranes that increasethe surface area of blood-rich tissue exposed to air.5. How do antscommunicate?________________________________________________________________________340Chapter 28Arthropods use antennae to detect movement,sound, and chemicals with great sensitivity.Antennae are stalklike structures that allowarthropods to detect changes in the environment.Antennae also are used for sound and odor communication. Ants and other arthropods are able tocommunicate with each other by pheromones.Pheromones (FER uh mohnz) are chemical odorsignals given off by animals.
For an ant to communicate the presence of food to another ant, thefirst ant releases a pheromone. Antennae sense theodor, which signals to the second ant that food ispresent. Pheromones signal animals to engage in avariety of behaviors. Some are used in scent trails.Others are important for mating behavior.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What kinds of respiratory structuresdo arthropods have?NameDateClassSection28.1Characteristics of Arthropods, continuedAccurate vision is important to arthropods. Most arthropodshave one pair of large compound eyes and three to eight simpleeyes.
A simple eye is a visual structure with only one lens that isused for detecting light. A compound eye is a visual structurewith many lenses. Each lens registers light from a tiny portion ofthe field of view. The total image that is formed is made up ofthousands of parts. The multiple lenses of a flying arthropod,such as a dragonfly, help it to analyze a fast-changing landscapeduring flight.Arthropods have well-developed nervous systems.
The nervoussystem processes information coming in from the sense organs.The nervous system consists of a double ventral nerve cord, ananterior brain, and several ganglia. Arthropods have ganglia thathave become fused. These ganglia act as control centers for thebody section in which they are located.6. What is the differencebetween a simple eye anda compound eye?________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are other arthropod body systems?Arthropod blood is pumped by a heart in an open circulatorysystem. Vessels carry blood away from the heart.
The blood flowsout of the vessels, bathing the tissues of the body. Blood returnsto the heart through open body spaces.Arthropods have complete digestive system. They have amouth, stomach, intestine, anus, and various glands that producedigestive enzymes.
The mouthparts of most arthropods includeone pair of jaws called mandibles (MAN duh bulz). Themandibles are adapted for holding, chewing, sucking, or bitingthe different foods eaten by arthropods.A Sand flies and other insectsthat feed by drawing bloodhave piercing blades orneedlelike mouthparts.READING ESSENTIALSB The rolled-up sucking tube ofmoths and butterflies can reachnectar at the bases of long,tubular flowers.C The sponging tongue of thehousefly has an openingbetween its two lobes throughwhich food is lapped.Chapter 28341NameDateClassSection28.1Characteristics of Arthropods, continuedMost arthropods that live on land get rid of wastes throughMalpighian (mal PIH gee un) tubules. In insects, the tubules areall located in the abdomen.
Malpighian tubules are attached to andempty directly into the intestine.The muscular system is well-developed in arthropods. In humanlimbs, muscles attach to bones. In arthropod limbs, the musclesattach to the inner surface of the exoskeleton. An arthropod muscle attaches to the exoskeleton on both sides of the joint.How do arthropods reproduce?________________________________________________________________________Most arthropod species have separate males and females andreproduce sexually. For land species, fertilization is usually internal.For aquatic species, fertilization is usually external. A few species,such as barnacles, are hermaphrodites, animals with both maleand female reproductive organs. Some species, such as bees, ants,aphids, and wasps, exhibit parthenogenesis.
Parthenogenesis(par thuh noh JE nuh sus) is a form of asexual reproduction inwhich a new individual develops from an unfertilized egg.Reproductive diversity has contributed to the success of arthropods. There are more arthropod species than all other animalspecies combined.◗ After You ReadMini Glossaryappendage (uh PEN dihj): any structure, such asa leg or an antenna, that grows out of ananimal’s bodymandibles (MAN duh bulz): in most arthropods,mouthparts adapted for holding, chewing,sucking, or biting various foodsbook lungs: gas exchange system found in somearthropods where air-filled chambers haveplates of folded membranes that increasethe surface area of tissue exposed to airmolting: in arthropods, the periodic shedding ofan old exoskeletoncephalothorax (se fuh luh THOR aks): structurein some arthropods formed by the fusion ofthe head and thoraxcompound eye: in arthropods, a visual systemcomposed of multiple lenses; each lens registers light from a small portion of the fieldof view, creating an image composed ofthousands of partsMalpighian (mal PIH gee un) tubule: in arthropods, tubules located in the abdomen thatare attached to and empty waste into theintestine342Chapter 28parthenogenesis (par thuh noh JE nuh sus): typeof asexual reproduction in which a newindividual develops from an unfertilized eggpheromones (FER uh mohnz): chemical signalsgiven off by animalssimple eye: visual structure in arthropods thatuses one lens to detect lightspiracles (SPIHR ih kulz): in arthropods, openingson the thorax and abdomen through whichair enters the tracheal tubestracheal (TRAY kee ul) tubes: hollow passages insome arthropods that transport air throughout the bodyREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.7.
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