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DIATOMEJE POD ELEKTRONSKIM MIKROSKOPOM Kremenaste alge so velik dejavnik v ekosistemu, vendar premajhne, da bi jih lahko videli s prostim očesom. Tudi z najboljšim optičnim mikroskopom se jim ne približamo dovolj. Vso raznolikost in bogastvo zapletenih struktur, ki ga skriva kremenasti skelet teh alg, nam razkrije šele slika, ki jo prikaže vrstični elektronski mikroskop VEM ali po tuje »scanning«, elektronski mikroskop SEM. Brez dvoma je VEM čudovito orodje, ki pokriva skoraj vse potrebe pri raziskavah površinskih struktur kremenastih alg. nikov in filtrov prenaša na zaslon, na katerem se — točka za točko in vrsta za vrsto — sestavlja slika preiskovane strukture. Lahko razumemo, da kvaliteto, ločljivost in sporočilno vrednost slike določata velikost slikovnih točk in gostota rastra, po katerem se premika žarek; povečava pa je razmerje med površino, ki jo elektronski žarek otipa na preparatu, in površino zaslona, na katerem nastaja slika. Povedano drugače, povečava pove, kolikokrat je alga, ki jo opazujemo, manjša od njene slike na zaslonu. Sodobni komercialni VEM mikroskopi omogočajo povečave od približno 10 do 1.000.000–krat in dosegajo ločljivost do 1nm. Pri tem pa velja, da dejanska povečava kot tudi realna ločljivost mikroskopskega posnetka nista odvisni samo od zmogljivosti mikroskopa, temveč sta v veliki meri odvisni tudi ali predvsem od kakovosti vzorca in nekaterih drugih dejavnikov. Elektronski mikroskop je zajeten in zapleten stroj. Poleg množice električnih in elektronskih sklopov vključuje tudi zapleten vakuumski sistem. V koloni mikroskopa, v kateri je tudi prostor za preparat, vrsta črpalk vzdržuje podtlak – vakuum, ki omogoča formiranje in upravljanje elektronskega snopa. Vzorec, ki ga bomo raziskovali, mora biti zato obstojen v vakuumu, biti mora odporen tudi na bombardiranje z elektroni v elektronskem žarku, predvsem mora imeti čisto površino, kajti velika povečava razkrije tudi najbolj drobne packarije. Slika pri tej vrsti mikroskopa ne nastane naenkrat, tako kot smo navajeni v vsakdanjem življenju, temveč postopoma, korak za korakom. Snop elektronov je usmerjen v točko na površini preparata. Odklonski sistem mikroskopa premika (»skenira«) snop elektronov po površini preparata po vnaprej določenem rastru. Signal, ki nastane ob zadetku žarka s površino preiskovanega vzorca, se iz detektorjev preko ojačeval- dr. Kazimir Drašlar Vrstični elektronski mikroskop JEOL JSM 7500F na Oddelku za biologijo Biotehniške fakultete v Ljubljani, na katerem so nastale mikrografije kremenastih alg za razstavo na prostem. The scanning electron microscope JEOL JSM 7500F in the Department of Biology, Biotechnical Faculty in Ljubljana, where the micrographs of diatoms for the outdoor exhibition published also in this publication were commencing. Poenostavljena shema delovanja vrstičnega elektronskega mikroskopa A simplified scheme of SEM and its working principle 8
DIATOMS UNDER THE ELECTRON MICROSCOPE Diatoms are a great factor in the ecosystem yet they are too small to be visible with naked eye. Even with the best optical microscope, we cannot come near enough. The whole diversity and richness of complicated structures hidden in the siliceous skeleton of these algae could be revealed only by scanning electron microscope (SEM). There is no doubt SEM is a wonderful tool covering almost all the needs that appear in the research work on surface structures of diatoms. Modern commercial SEM microscopes enable magnifications from approximately 10 to 1,000,000 times allowing image resolution to 1 nm. However, it must be stressed that real magnification as well as real resolution of micrograph depend not only upon the capacity of the microscope but to a high degree also upon the sample quality as well as some other factors. Electronic microscope is sizable and complicated machine. Along with a number of electric and electronic complexes it includes also a complicated vacuum system. In the microscope column where is also a chamber for the sample, a series of pumps is maintaining vacuum which enables forming and managing of the electron beam. That fore the sample which we will investigate must be stable in vacuum, resistant to bombardment with electrons within electron beam and has to have a clean surface, while high magnifications reveal even the finest muck. In this kind of microscope the image doesn’t appear at a time like we are used in everyday life, rather it is appearing gradually, step by step. Electron beam is focused to a spot in the sample surface. Microscope tilting system scans the electron beam in a raster fashion over a rectangular area of the sample surface. The signal emerging from the collision of the beam with the surface of the sample investigated is transmitting from detectors via electronic amplifiers and filters to the screen where — point after point and row after row — the picture of the investigated structure is constituted. We could understand that the quality, resolution and communication value of the image are determined by the size of image points and by the density of the raster along which the beam is moving; magnification, however, results from the ratio of the dimensions of the raster on the specimen and the raster on the display device. In other words, magnification tells us, how many times alga, which we are observing is smaller from its image on the screen. Dr. Kazimir Drašlar 9
Page 1: Razkrita čudesa reke BIOTSKA PESTR
Page 5 and 6: Pobliže ko opazujemo nek pojav, bo
Page 7 and 8: THE INVISIBLE BEAUTY OF DIATOMS Tin
Page 9: limit and throw away what we feel i
Page 13 and 14: DIATOMS: WHEN ESSENTIAL BECOMES VIS
Page 15 and 16: Revealed River Wonders and subtitle
Page 17 and 18: Whenever in the story of diatoms it
Page 19 and 20: DIATOMS, LOOPED INTO DRAŽ KNITWEAR
Page 22 and 23: 20 40 %
Page 24 and 25: Diatomeje so posebna skupina mikros
Page 26: Alge. Je to sluzasta obloga rečneg
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Page 38: Diatomeje so svetovljanke, zato te
Page 42: Geografska in krajinska pestrost Sl
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