Biology - An Illustrated Guide to Science (794127), страница 23
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This is made up ofparenchyma cells, and waterand minerals from the soilcan flow easily betweenthese cells.endodermisxylemstelecortex(parenchyma)phloemStele: transverse sectionThe steleA continuous cylinder of cells calledthe en doderm is surrounds the innerpart of the root, the stele. Endodermalcells have a waterproofing substancecalled su berin in their cell walls, whichblocks movement of water from thecortex between the cells. Water nowhas to pass through the cells ratherthan between them: this gives theplant a degree of control over waterand mineral salt movement into thestele.● The pericycle conducts water andnutrients inward to the xylem andphloem.● The stele is the central core containingthe xylem and phloem tissues.
This isusually arranged in a cross shape withxylem in the middle. As the root agesthe structure changes to the bundlesmore typical of the stem.endodermispericyclexylemphloemsieve tubecompanioncellspace filled withparenchyma© Diagram Visual Information Ltd.●passage cell134MAINTENANCEKey wordsactive processosmosistranspirationxylemTransport: water andminerals in plantsTransport of waterand mineralsGeneralized plantXylem tissuesLeaf: transverse sectionair spacephloemxylem cuticleepidermispalisademesophyllWater movement in plants is largelythrough xylem vessels.● Xylem vessels are made of elementsstacked on top of each other. The endwalls have been lost, effectively leavingempty cylinders reaching from theroot to the leaves.●spongymesophyllstemAbsorption of water andsaltsWater is absorbed through the root byosm osis.
Mineral salts are similarlytransported in solution and pass upthe plant through the xylem.● Some minerals are also absorbed byactive processes requiring an energyinput by the plant.epidermis●shootstomaguard cellStem: longitudinal sectionepidermisparenchyma (cortex)fiberscambiumphloemxylempithTranspiration suctionWater is constantly evaporating fromthe aerial parts of the plant.
Thisprocess is called tran spiration andoccurs mainly through the leavesduring daylight hours. In optimalconditions a typical herbaceous plantcan transpire up to 40 times its ownweight in water every day.● Transpiration reduces waterconcentration in the leaves. This, inturn, creates a force on the water inthe veins sucking water outward. Theveins are continuous with the xylemvessels, so the force is transmittedthrough the water column all the waydown to the roots. This force, calledtranspiration suction, pulls water upthe plant. It requires no energy inputfrom the plant.© Diagram Visual Information Ltd.●Root: longitudinal sectionparenchyma (cortex)xylemepidermisrootroot hairroothairflow of water and mineralsevaporation of water from leaf (transpiration)soilparticles135Transport: food in plantsMAINTENANCEKey wordsTransport of foodGeneralized plantactive transportglucosephloemphotosynthesisvascular bundleLeaf: transverse sectioncuticlexylemxylemphloemSources and sinksFood is manufactured in the leavesand green stems of plants byphotosyn thesis.
These areas are calledthe sources.● Food is used in all parts of the plant.Some areas are particularly adapted tostore food, for example tubers inpotatoes and many fruits in floweringplants. These areas are called sinks.●epidermispalisademesophyllstemshootspongymesophyllLeaves and stemsLeaves create glu cose from carbondioxide and water using light as anenergy source. Glucose is difficult totransport through plants because itrequires large amounts of water.Leaves convert this glucose intoanother sugar called sucrose, which iseasier to move.● Veins in the leaf contain vascu larbu n dles that contain two types ofconducting vessels: xylem andphloem .● Phloem transports sugars away fromthe leaf.● Xylem conducts water and dissolvedminerals from the roots to the stemand leaves.●epidermisStem: longitudinal sectionepidermisparenchymaleafxylemcambiumphloemRoots and fruitsVascular bundles in the leaf connectwith similar structures in the roots.Each sieve tube, a part of the phloem,is continuous with those in the roots.Sugar is loaded in and passes down byactive tran sport.
In the roots thesugar is taken out of the phloem tubesand converted to starch for storage, oris used to keep the root alive.● Fruits and flowers require sugarbecause they do not carry outphotosynthesis.flow of food© Diagram Visual Information Ltd.root●136MAINTENANCEKey wordsarterycapillaryhemoglobinveinventricleTransport: frogArterial systemlingualcutaneoussubclavianThe circulatory system of the frog hasarteries that carry blood away fromthe heart and vein s that carry it back.● Arteries and veins are named after theorgan they take blood to (in arteries)or away from (in veins).● Organs have a single artery and veinalthough it may subdivide into smallervessels before it enters the organ.Inside the organ the vessels subdividefurther to form capillaries that areultimately one blood cell wide.
No cellin the body is further than 0.004 inch(0.1 mm) from a blood capillary.Materials are exchanged with theblood at this point.right atriumt runcusar teriosusexternalcarotidFrogs have a well-developedcirculatory system with blood that isheld within tubes that penetrate thewhole body.● Frog blood is supplied with a form ofhem oglobin that reacts reversibly withoxygen to collect oxygen from theexchange surfaces and deliver it to thecells of the body.Circulatory system planVentral viewgastricinternalcarotidCirculatory system●Heartanterior mesentericleftatriumpulmonaryhepaticsystemic archgenitalrenalposteriormesenteric●Frog heartThe heart pushes fluid around thevessels to maintain a constant supplyof fresh oxygenated blood.● With a single ven tricle, the frog heartis less developed than mammalianhearts.dorsal aortaventricleiliacsciaticHeartV enous systemmandibularlingualDorsal viewbrachialmusculocutaneousanterior vena cavasubclavianpulmonaryveininternaljugularsinusvenosusrightatriumexternaljugularsubscapularanteriorvena cavaleftatrium●pulmonaryhepaticposteriorvena cavahepaticportalgenital© Diagram Visual Information Ltd.mesentericanteriorabdominalrenalrenalportalventriclefemoralposterior vena cavasciaticdirection ofblood flow137Respiration: plantsMAINTENANCEKey wordsRespiration in plantsLeaf: transverse sectiondiffusionlenticelphotosynthesisrespirationroot haircuticleepidermispalisademesophyllRespiration in plantsPlants carry out respiration at all timesof the day and night.● During daylight hours, the plantobtains all the oxygen it needs as a byproduct of photosyn thesis.
The leavesare thus net exporters of oxygen.● During the night, or whenphotosynthesis is halted for someother reason, plants take in oxygen forrespiration by diffu sion through theleaves.●veinspongymesophyllair spaceGeneralized treeepidermisstomaleaf: transverse sectionguard cellLenticel: longitudinal sectionremains ofepidermisWoody stemsWoody stems do not carry outphotosynthesis, so they need toobtain oxygen directly from theatmosphere.● The bark of trees prevents thepassage of oxygen, so plants havestructures called len ticels, which arebreaks in the bark covering. Oxygencan diffuse into the stem throughthese.
Once inside the plant, the gasmoves in solution between the cellsby diffusion.● Lenticels have cells that are lesstightly packed than most cells in thestems to provide an increasedsurface area for the exchange ofoxygen with the atmosphere.●canopy(foliage)lenticel:longitudinalsectioncorkt runkbranchcorkcambiumrootsloose cork cellsRoot: longitudinal sectionroot:longitudinal sectionp arenchymaRootsepidermisSince roots do not receive light, theycannot carry out photosynthesis, soare always net importers of oxygen.● The gas diffuses into the root throughroot hairs, which penetrate air spacesin the soil.cabon dioxidesoil particlesoxygen© Diagram Visual Information Ltd.●root hair138MAINTENANCEKey wordsconcentrationgradientdiffusiongaseousexchangeRespiration: gas exchangeacross body surfacesGas exchange across body surfacesAmebaHydraOxygen sourceOxygen is available in the environmenteither as a gas or dissolved in water.● The point at which oxygen passes intothe body of an animal is called therespiratory surface.
It must be keptmoist.●Animals withoutcirculatory systemsIn animals without specializedcirculatory systems, such as amebasand Hydras, oxygen dissolves in themoisture on the surface of the bodyand passes by diffu sion to adjacentcells. Carbon dioxide passes the otherway.● Since respiration uses up oxygen andproduces carbon dioxide, acon cen tration gradien t in the gasesensures transport in the correctdirection.
An increase in activityincreases the gradient, leading to afaster rate of diffusion.● However, since diffusion cannotrapidly move materials over largedistances, a size limitation is imposedon simpler animals. To reduce thislimitation, a number of these animalshave flattened body shapes to increasethe surface available for gaseou sexchan ge and reduce the distance theoxygen needs to diffuse inside thebody e.g., flatworms.●FlatwormFlatworm body wall: vertical sectiondorso-ventral musclegland cellflatwormbody wall:verticalsectionlongitudinal musclecircular muscleepidermisEarthwormEarthworm body wall: vertical sectionoxygenepidermisearthwormbody wall:verticalsection●© Diagram Visual Information Ltd.ciliabasementmembraneAnimals withcirculatory systemsThe earthworm has a simplecirculatory system that transportsoxygen absorbed through the skindeeper into the body.● Carbon dioxide produced inside thebody is moved by the samemechanism in the opposite direction.This allows the earthworm to have arounder body shape than the moreprimitive flatworms.parenchymacarbon dioxidecuticlecapillary139Respiration: respiratorysurfaces in animalsMAINTENANCEKey wordsgilllungtracheoleSurfaces for gaseous exchange in a range of animalsEntire body surface (Hydra, earthworm)Flattened body (flatworm)Mass flowgutflattened body surfacegutbody surfaceIn the simplest animals, the respiratorysurface is the whole of the externalbody surface.
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