Biology - An Illustrated Guide to Science (794127), страница 17
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The presence ofthe chloroplast means that Spirogyracan carry out photosyn thesis.● Pyren oids are small structuresembedded in the chloroplast that areconcerned with the formation ofstarch.● The cell wall of Spirogyra is made upof cellu lose, a complex carbohydratethat stiffens the cell wall. Inside thisare the plasma membrane and a thinlayer of cytoplasm surrounding acentral vacu ole enclosed by amembrane called the tonoplast.● The large nucleus is suspended in thecenter of the cell by strands ofcytoplasm.●Multicellular protists●Single cell: longitudinal sectioncell wallnucleuschloroplastpyrenoidcytoplasmic strandcytoplasmic liningThe Spirogyra is unusual in that it is amulticellular protist and can form largemats of intertwined filaments (top leftdiagram) clearly visible to the nakedeye.Spirogyra cells join end to end tocreate long filaments that are clearlyvisible with the naked eye.
Growth ofthe filament occurs when a cell dividesinto two. Any cell in a filament is ableto do this.© Diagram Visual Information Ltd.plasma membranesingle cell98DIVERSITYKey wordsenzymemyceliumorganic matterphotosynthesissporeKingdom Fungi: RhizopusRhizopusMycelium on stale breadmycelium(networkof hyphae)ClassificationFungi cannot carry out photosyn thesis.En zym es secreted by the fungus digestorgan ic m atter externally before it isabsorbed into the cell.
Many fungihave complex reproductive structuresthat are often the only part of theorganism visible to the naked eye.● Rhizopu s is a mold that grows ondamp bread and other foods. It is seenas a white network of fine hairs, oftenwith very small black pinheads.●Mycelium (network of hyphae)sporangiumStructureThe main body of the fungus is anetwork of tiny interconnectedthreads called hyphae. Hyphae aretubular structures that can branch andfuse to produce a network called am yceliu m .● Fungi do not have true cells: hyphaeare cut up into cell-like sections, butthe cross walls do not fully join in themiddle to separate these parts.● The large surface area provided by themycelium allows both the rapidsecretion of enzymes to break downfood substrates and the absorption ofthe products into the body.● Certain hyphae are specialized toproduce spore-containing bodiescalled sporangia.
The sporangiaare often black in color.These burst when ripeto release single-celledspores that floaton the air untilthey find asuitableplace© Diagram Visual Information Ltd.●sporangiophore(stalk of sporangium)hyphato grow. Here they produce anothermycelium.hyphae growing in food99Kingdom Plantae:classificationDIVERSITYKey wordscellulosechlorophyllsporeTree diagram of PlantaePlantaePlantaeMembers of the Plantae all share anumber of features: they all possesscellu lose cell walls. The majority alsopossess chlorophyll and have vesselsor tubes inside their bodies to carrywater.● Most are multicellular, and some arevery large.● The Kingdom Plantae is divided intoBryophyta, which lack anatomicaldifferentiation between leaves androots, and Tracheophyta, which arecharacterized by the presence ofvascular tissue and the differentiationof parts into roots, stems, and leaves.Tracheophyta, in turn, are divided intoPteriodophyte, plants that reproduceby spores, and Spermatophyta, plantsthat produce seeds.●BryophytaTracheophytaPteridophytaBryophyta●These are the mosses and areprimitive plants that are small(they never grow more than a fewcentimeters high) and can only survivein damp areas.
They reproduce byspores.PteridophytaSpermatophyta●These are the ferns and are larger thanmosses but are still confined to fairlydamp places. They reproduce byspores.●The gymnospermae includeconiferous trees and include somevery large plants. They produce seedsbut do not have full-developedflowers.Angiospermae●GymnospermaeAngiospermaeThese are called the flowering plantssince they have both true flowers andseeds and fruits. They are the mostsuccessful and advanced plants andcan survive a huge range ofconditions.© Diagram Visual Information Ltd.Gymnospermae10 0DIVERSITYKey wordsgametegametophytephotosynthesissporesporophytezygoteKingdom Plantae:BryophytaLiverwortMale (receptaclecarryingantheridia) plantantheridiophoreBryophyta●Members of the bryophyta are small,simple green plants that carry outphotosyn thesis.
They are restricted torequire water for reproduction. Theyinclude the liverworts and the mosses.gemma cupthallusrhizoidsLiverwortsLiverworts consist of a flattenedbranching structure called a thallus,which has no obvious division intoleaves and stems. Root-like structurescalled rhizoids grow out of the lowersurface to anchor the plant and to takeup nutrients.● The sexual parts of liverworts arecontained in inconspicuous structuresknown as antheridia (male) andarchegonia (female). These developon separate plants and are borne onstalked antheridiophores andarchegoniophores, respectively.Fertilization takes place whenraindrops splash sperm to femaleplants.
The sperm swim down thecanal in the archegonium to thechamber containing the egg. Theresulting zygote begins the sporophytegeneration. Spores subsequentlydevelop and are dispersed by aircurrents. Once they settle in a moistenvironment, they germinate, and thegametophyte generation begins again.sporophyte●Female (thallusreceptaclecarryingarchegoniarhizoidsMosssporangium(capsule)sporophyteseta“ leaves”surroundingarchegonia●© Diagram Visual Information Ltd.archegoniophoregemma cupMossesMosses have clearly identified stemswith leaves attached.● Reproduction involves sporophyte andgametophyte generations. The tinysporophyte (spore-producing mossplant) is attached to the top of themoss gametophyte (gamete plant). Itconsists of a seta (slender stalk) and aterminal capsule (sporangium), whichproduces spores.
As the sporophytedries out, the capsule releases itsspores, which will grow into a newgeneration of gametophytes upongermination.) plantantheridia“ leaf”“ stem”rhizoids10 1Kingdom Plantae:PteridophytaDIVERSITYKey wordsbilateralsymmetrygametegametophytesporeTypical pteridophyteSporophyte: external viewsporophytezygotePteridophytaMembers of the Pteridophyta rangefrom small clubmosses to very largetree ferns, which can grow to 9 feet(approx. 3 m) with fronds that stretchup to 6 feet (approx. 2 m) in length.● All pteridophytes are restricted todamp areas, although they are able tosurvive drier conditions thanliverworts and mosses.●pinna(leaflet)Adult form●frond(leaf)ReproductionPinna:lower surfacebases of previousyear’s frondsroots (adventitious)midrib ofpinnasorusrachis(stem)pinna (leaflet)rhizomepinnuleThe visible fern plant is the sporophytegeneration.
It produces spores fromsporangia borne on the underside ofthe leaf. These sporangia are calledsori and produce spores that resemblea rusty brown powder.● The spores produced by the sori willdevelop into the gam etophytegeneration, which gives rise toreproductive cells. This plant is verysmall and requires very dampconditions to survive. If theseconditions are available, it will developand produce gam etes that will fuse toproduce a zygote (a fertilized ovum), ifgametes of the other gender areavailable.
This zygote then grows toproduce an adult fern.●© Diagram Visual Information Ltd.rachis(stem)The typical form for a pteridophyte isa central rhizome (a horizontalunderground stem) with long frondsgrowing out of it. The fronds supportflat leaves, which grow out from acentral stalk. The leaves are bilaterallysym m etrical with a central stalk andflat leaflets called pinna on either side.10 2DIVERSITYKey wordsdiploidsecondarythickeningseedKingdom Plantae:GymnospermaeTypical gymnospermPine treeapicalbudconesSeed plantsGymnospermae are plants thatproduce true seeds. These seeds aredifferent from the spores produced bymosses and ferns because they arediploid—they contain pairs ofchromosomes—and develop directlyinto adult plants.● Gymnosperms are able to survive drierconditions than bryophytes andpteridophytes and are found in manyharsh environments.● Gymnosperms are divided into threemain groups: coniferous plants likepines, fernlike plants called cycads,and a small and rare group of highlyspecialized plants called gnetales.●conepair of leaves(needles)cone before fertilizationAdult formPines and cycads both showsecon dary thicken in g in their stems,which means that they can form tall,strong structures.
The woody stemsgive rise to branches that grow outfrom the sides and, in turn, producesmaller branches.● Growth occurs at the apical bud at theapex or terminal position on thebranch.● The leaves of all gymnosperms arewaxy and resist water loss well.ovuliferous scale●ReproductionGymnosperms produce enclosedseeds held in cones. Male and femalecones are separate structures. Thefemale cones tend to be woody andare covered by ovuliferous scales,which protect the developing seeds. Inthe mature cone, the scales curl torelease the seeds.● Cones that do not separate open upso that the seeds, which are equippedwith a wing to aid dispersal by thewind, are released.© Diagram Visual Information Ltd.●conescone before fertilizationcone after fertilizationconeOvuliferous scale:upper surfacecone after fertilizationovuliferousscalematureseedwing ofseedovuliferous scale:upper surface10 3Kingdom Plantae:AngiospermaeDIVERSITYKey wordsanthercarpelgameteovaryovuleTypical angiospermPlant bodypistilpollenstamenstigmastyleterminal budFlowering plantsflowerAngiospermae are plants that producetrue seeds and fruits from flowers.● Angiosperms are the most successfulgroup of plants: they can survive amuch wider range of environmentsthan other groups.● Almost all human food comes fromangiosperm species, with the grassfamily, including wheat, corn, rice, andbarley, contributing the largestproportion.●leafstemshootaxillary budAdult formtap rootAngiosperms are a very wide groupand range from tall woody trees tosmall floating water plants with almostno stem.
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