Biology - An Illustrated Guide to Science (794127), страница 24
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In animals with gills orlu n gs, the surface is contained withinthe body.● The oxygenating medium must beactively pumped across this surface toprovide constant fresh supplies. This isan example of mass flow.●GillsGills are organs with extensive foldedmembranes supplied with bloodvessels.● In internal gills, a mass flowmechanism maintains a flow of theoxygenating medium: the watercontaining the dissolved oxygen.● Internal gills are less susceptible tomechanical damage than external gills.●External gills (young tadpole)Tracheal system (grasshopper)external gilltracheoleTracheolestracheaInsects have thin tubes calledtracheoles to carry air deep into thebody.● Insects have very limited mass flowsystems.
This prevents growth ofinsects above a certain size.●gutspiraclegutLungsInternal gills (fish)Lungs (human)gutinternal gilllunggutLungs have a very large surface areainside the body, and a system ofmuscles and tubes maintains the flowof air across these surfaces.© Diagram Visual Information Ltd.●140MAINTENANCEKey wordsconcentrationgradientgillRespiration: fishRespiration in fishExternal viewmouthHead (operculum removed)gill archgill filamentsOxygen sourceOxygen is available to fish dissolved inwater.● The oxygen that forms part of watermolecules cannot be used by fish.●Mass flowFish have two mass flow systems: oneto force oxygenated water across therespiratory surface and one tocarry oxygenated bloodaround the body.● Water is taken in through themouth and pumped over thegill surfaces.
The flow is oneway, with water leavingthrough the operculum, a flapof tissue covering the exitsfrom the gills behind the headof the fish.●operculumGillgill archefferent vessel (carrying blood from the heart)afferent vesselgill plategill filamentgillDetail of gill filamentgill plateGill structureGills are made of a series ofarches that are supplied with astack of flattened structures called gillfilaments.● The gill filaments are well-suppliedwith blood through an afferent vessel(a vessel carrying blood toward theheart).
Blood passes along thefilaments and into gill plates that areheld perpendicular to the filament. Itis in the gill plates that gaseousexchange occurs.● Blood flows through the plate in theopposite direction to the water. Thiscountercurrent multiplier systemmeans that the freshest water meetsthe most oxygenated blood. Theoxygen con cen tration gradien t ismaintained further back because,although some of the oxygen has beenremoved from the water, it is nowpassing over the least oxygenatedblood.© Diagram Visual Information Ltd.●gill filamentdetail of gill filamentVentilationIntake of waterExpulsion of watermouth closedmouth opengill filamentgill filamentoperculum openoperculum closedflow of waterflow of bloodoxygencarbon dioxide141Respiration: frogMAINTENANCEKey wordsRespiration in frogsbuccal cavitygaseousexchangegilllife cyclepharynxnostrilglottismouthskinlungSites of gaseous exchangeIn common with all amphibians, frogsspend part of their life cycle in waterand part on land.
This requires acomplex mixture of mechanisms forgaseou s exchan ge that develop andchange throughout the lifetime of thecreature.● The adult frog uses lu n gs and thesurface of its whole body for gaseousexchange. The larval stage (tadpoles)uses external gills.●floor of buccal cavitylungVentilationMoving air into and out of the lungs iscalled ventilation. Ventilation ensures aconstant supply of fresh oxygen andallows the removal of carbon dioxiderich air. However, it also leads to theloss of moisture in exhaled air.● The floor of the bu ccal cavity (themouth or oral cavity) can be droppedin the frog to create a zone of lowpressure.
This sucks air in, and if theentrance to the lungs is closed thismust come from the outside throughthe nostril.● Closing the nostril and raising thefloor of the buccal cavity creates a risein pressure. If the tube to the lungs isopened at the same time, air is forcedinto the lungs where gaseousexchange can take place. This allowsinhalation.● Exhalation occurs when theprocedures are reversed.Ventilation of lungsInhalationnostrilpharynxmouthglottisfloor ofbuccal cavitylungExhalationoxygenmovement of aircarbon dioxidemovement of floor of buccal cavity© Diagram Visual Information Ltd.●142MAINTENANCEKey wordscentral nervoussystemspinal cordCoordination:nervous systemsNervous systemsEarthwormHydramouthLongitudinal section anterior endt entaclepharynxNerve netscerebral ganglion(brain)The simplest nervous systems are netswith no central control.● For example, animals like Hydra havea nervous system that is spread acrossthe entire body with no distinct headarea.●segmentalnervesHeadsAs animals developed the ability tomove in a particular direction, theybegan to develop heads.
This is thefront end of the organism and tends tohave the highest concentration ofsense organs to gather informationabout the environments into whichthe animal is moving.● Processing this sensory informationrequires a large amount of nervoustissue, so the nerve tissue close tothese organs began to swell in size.This was the beginning of a brain.●network ofnerve cellsmouthnerve collarventralnervecordGrasshopperLateral viewcompound eyeantennaCentral nervous systemsAt the same time as the heads weredeveloping, animals were alsodeveloping backbones and spinalcords. Vertebrates have a welldeveloped spin al cord that can carryinformation to and from the brain.The brain and spinal cord togetherare called the cen tral n ervou ssystem .● Invertebrates like the grasshoppertended to develop smaller brainscalled ganglia, which were distributedthroughout the body, rather than abrain and spinal cord arrangement.Even in these cases, however, themost important ganglion was in thehead near the sense organs.ganglion© Diagram Visual Information Ltd.●cerebral ganglion (brain)nerve collarventralnerve cordganglionDorsal viewcerebral ganglion (brain)nerve collarventral nerve cordsegmental nervesganglion143Excretion andosmoregulation: ProtistaMAINTENANCEKey wordscontractilevacuolediffusionmetabolismosmoregulationExcretion and osmoregulation in amebasOsmoregulationContractile vacuole (electron microscope)ExcretioncellmembranemitochondrionosmosisExcretion andosmoregulationExcretion is the removal of the wasteproducts of m etabolism from theorganism.● Osm oregu lation is the maintenance ofthe correct water potential within acell.
Thus, osmoregulation is notprimarily concerned with the productsof metabolism.●Excretion●contactilevacuolevesicle fusingwith vacuolemembranenucleuscontractile vacuolecytoplasmvacuole membranevesicle containing waterContractile vacuole formation and dischargecell membranecontractile vacuole(electron microscope)cytoplasmnucleuscarbon dioxideWater constantly enters protists likeameba due to osm osis. If this waterwere not removed, the cell wouldswell and could burst. Even before thisoccurred, the cell contents would bediluted to such an extent that essentialmetabolic processes could bedisrupted.● The ameba collects water in the cell byan active process and pumps it into asac called a con tractile vacu ole.
Thisswells as it gains water and when fullmigrates to the edge of the cell, fuseswith the cell membrane, and releasesthe water into the environment.●contractilevacuolewasteOsmoregulationwater© Diagram Visual Information Ltd.OsmoregulationWaste products of metabolism inProtista diffuse through the cellmembrane. Since the protists areunicellular organisms, diffu sion israpid enough to clear away allunwanted chemicals, and nospecialized excretory structures arerequired.144MAINTENANCEKey wordsmusclesegmentLocomotion: earthwormLocomotion in earthwormsTransverse section: intestinal regioncoelom(hydrostatic skeleton)Pushing and pulling●Earthworms move through the soil byalternately contracting and relaxingsets of m u scles.
This makes theearthworm stretch or contract bodysegm en ts, which are pushed or pulledthrough the soil.Circular muscles contracted,longitudinal muscles relaxedintestinesegment long and thinlongitudinal musclecircular muscleepidermisseptum (dividing wallbetween segments)SetaeSetae are small hair-like projectionsfrom the surface of the earthworm’sbody.● They can be extended or retracted bymuscles.
When extended, theyeffectively anchor that part of theearthworm in place.●Longitudinal muscles contracted,circular muscles relaxedsegment short and fatMovementsetaprotractor muscleseptumsetasetastationary regionextending regionanterior endsegmentextending regionMovementstationary region© Diagram Visual Information Ltd.nerve cordsetaretractor muscleworm at restAn earthworm at rest tends to be shortand fat, with its circular musclesrelaxed.● To move, the earthworm extends setaeat the back of its body and contractscircular muscles in the segments at thefront. The contracting musclessqueeze on the body contents, raisingthe pressure, and the segmentselongate.● The earthworm then extends setaefrom the frontmost segments andretracts them in the rear segments.Circular muscles in the front relax, andlongitudinal muscles contract. Therear segments elongate or are pulledslightly forward.● Step by step the front segmentscontract and fatten while the rearsegments are first elongated and thendragged forward.●retractingregion145Locomotion: grasshopperMAINTENANCEKey wordsLocomotion in grasshoppersantagonistic pairexoskeletonmuscleExternal viewabdomenthoraxheadwingExoskeletonGrasshoppers, as with all insects, havea rigid exoskeleton covering theirbody.● Mu scles are attached to the inside ofthe skeleton.● Joints in the exoskeleton allow thelimbs to bend.●leglimb movement(schematicsection of leg)wing movement (transverse section: thorax)Limb movementcuticle(exoskeleton)extensormusclecontractedpeg andsocketjointFlexedextensormusclerelaxedtendonpegWing movementflexor muscle relaxedflexor musclecontractedsocketWing movementTransverse section: thoraxt ergumUpstrokelongitudinalmuscles relaxeddorso-ventralmuscles relaxedwinglongitudinalmuscles contractedsternumThe muscles that move the wings upand down are attached to theexoskeleton.
Muscles running from thetop of the body to the bottom contractto pull the wings up. The elasticity ofthe exoskeleton and muscles runningalong the length of the body help topull the wings down.● Since the muscles moving the wingsare held inside the body, the wings canbe very light in weight. This makesthem easier to move and allows themto be larger, creating more downdraft,which helps the grasshopper to fly.●muscle attachmentDownstrokeThe rigid exoskeleton cannot bend,and joints can only operate in oneplane.
The joints are connected by apeg and socket arrangement. Thismeans that in order to allow a widerrange of movement limbs are brokenup into a number of sections with thejoint between each section allowingmovement in a different plane.● Muscles work in an tagon istic pairs asin mammals, with flexors bendinglimbs and extensors straighteningthem.●dorso-ventralmuscles contracted© Diagram Visual Information Ltd.Schematic section of legExtendedJoints146MAINTENANCEKey wordsbacteriophagebacteriumnucleic acidvirusObligate parasites●Reproduction: virusesReproduction in virusesBacteriophage structureheadcollarAll viru ses are obligate parasites,which means they cannot reproduceoutside a living host.sheath (contractile)BacteriophagesBacteriophages are a group of virusesthat infect and kill bacterial cells.● Bacteriophages typically have a headto their body that contains a length ofn u cleic acid. The head is connectedto a tail consisting of a sheath that cancontract and a base piece with fibersthat can attach to bacterial cell walls.● Particular bacteriophages attackspecific bacteria.●t ailt ail fiberLytic life cycleLytic life cycleLysis is the rupture and destruction ofa cell.● A bacteriophage attaches itself to theoutside of a susceptible bacteriu mwith its base plate.
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