Microscopes—tools for studying biodiversity

• detect, distinguish between organisms

• study structure of cells, tissues, organs

• determine locations of molecules

simple microscope

• 1 lens (eg magnifying glass)

• bends light so object appears larger

virtual image object lens eye

compound microscope

• >1 lens

• mag multiplies• so do optical problems

object obj. virtual eyepiece eye lens image (ocular)

optical terms

• magnification: how large appears compared to actual size

• resolution (resolving power): closest distance 2 objects can be, & still be distinguished as separate obj.

• resol dep on wavelength ()– shorter better. electron microscopes

lens resolution comparison

• human eye 0.2mm ruler in lab• light scope 0.2m 1000x better than

eye• electron scope ~ 2 nm 100x better than LM

100,000x better than eye

= micro• LM = light scope• EM = electron scope

scale

• 1mm = 1000 m = 1 million nm• human hair ~1/10 of mm = 100 m

• electron microscopy reveals viruses! 20 – 90 nm

• 1990s: 50 million/mL of seawater, soil

• Fig 6.2, p 95

image terms

• photograph--no scope• photomicrograph--photo taken

though scope– light micrograph– electron micrograph

LM

• Advantage: living cells & organisms

• colors (pigments)• movement• focus through depth of specimen

EM

• disadvantage: specimens dead

• electrons from filament • in vacuum• focus with electromagnetic lenses

TEMtransmission electron microscope

• electrons go through specimen

• make shadow• fine structure

inside of cells• many sections for

3-D structure

TEM

• can locate molecule w/antibody attached to gold particle

SEM scanning electron microscope

• electron beam scans specimen

• specimen electrons collected

• surface of object• 3-D view

LM contrast

• pigments• stains• brightfield--standard bright background• special techniques (Fig 6.3, p 96)

– polarized light– darkfield– differential interference contrast (dic)– phase contrast

fluorescencemicroscopy

• UV light source• specimen

emits light

• autofluorescence• tagged antibodies• reporter proteins

Confocal microscopy

• laser light source

• optical sections

• no out of focus blur

discovery of cells

• 1665 English scientist Robert Hooke

• first saw (cork) cells [cell = room]• compound microscope• (30x mag)• Royal Society, London

Hooke’s drawing of cork cells in Micrographiahttp://www.gutenberg.org/files/15491/15491-h/15491-h.htmsection 18, plate 11

Hooke’scompound microscop

e

http://www.arsmachina.com/hooke.htm

scientific literature

• primary lit. — original report of research– intro, materials & methods, results, discussion

• peer-reviewed

• secondary lit. — report about primary lit.

• ProcRSocL, Nature, PNAS, Science

discovery of microorganisms

• 1674 Dutch merchant Antony van Leeuwenhook

• first saw “animalcules”• protists, and later bacteria• simple microscope w/great lens• 275-295x mag

http://www.ucmp.berkeley.edu/history/leeuwenhoek.html

discovery of microorganisms

• 1676 Leeuwenhookwrote to Royal Society

@ singled celled organisms

• Hooke confirmed• first published bacteria• voucher specimens

http://www.ucmp.berkeley.edu/history/leeuwenhoek.html

Leeuwenhoek’s microscope

http://www.brianjford.com/wav-mict.htm

light micrograph of red blood cells photographed through this scope

• mid 1700smicroscopy popular science