Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Reason to Retrovirus » Respiration - External Respiration, Internal Respiration, Cellular Respiration, Glycolysis, Cirtric Acid Cycle, Electron Transfer Chain

Respiration - External Respiration

oxygen blood method diffusion

External respiration, commonly known as breathing, is the exchange of oxygen and carbon dioxide between an animal and its environment. Most animals use specialized organs or organ systems, such as lungs, trachea, or gills, for external respiration.

In all cases, exchange of gases between the environment and an animal occurs by diffusion through a wet surface on the animal which is permeable to oxygen and carbon dioxide. Diffusion is the random movement of molecules and causes a net movement of molecules from a region of high concentration to a region of low concentration. Thus, oxygen moves into an organism because its concentration is lower inside than in the environment (air or water); carbon dioxide moves out of an organism because its concentration is higher inside than in the environment.

Different organisms have different mechanisms for extracting oxygen from their environments. Below, animal-gas exchange mechanisms have been classified into five categories.

  1. Direct diffusion. Sponges, jellyfish, and terrestrial flatworms use this primitive method. In direct diffusion, oxygen diffuses from the environment through cells on the animal's surface and then diffuses to individual cells inside. The primitive animals that use this method do not have respiratory organs. Obviously, an animal with small surface areas and large volume cannot rely on direct diffusion, since little oxygen would reach the interior of the body. Microbes, fungi, and plants all obtain the oxygen they use for cellular respiration by direct diffusion through their surfaces.
  2. Diffusion into blood. Annelids (segmented worms) and amphibians use this method. In this method, oxygen diffuses through a moist layer of epidermal cells on the body surface and from there through capillary walls and into the blood stream. Once oxygen is in the blood, it moves throughout the body to different tissues and cells. While this method does not rely upon respiratory organs and is thus quite primitive, it is somewhat more advanced than direct diffusion.
  3. Tracheae. Insects and terrestrial arthropods use this method. In tracheal respiration, air moves through openings in the body surface called spiracles and then into special tubes called tracheae (singular, trachea) which extend into the body. The tracheae divide into many small branches which contact the muscles and organs. In small insects, air moves into the tracheae passively, whereas in large insects, body movements facilitate tracheal air movement. An advantage of tracheal respiration is that it provides oxygen directly to the muscles. Muscle cells use this oxygen, together with the carbohydrates and other energetic molecules in the hemolymph (insect blood), to generate the energy needed for flight.
  4. Gills. Fish and other aquatic animals use this method. Gills are specialized tissues with many infoldings, each covered by a thin layer of cells and impregnated with blood capillaries. They take up oxygen dissolved in water and expel carbon dioxide dissolved in blood. Gills work by a mechanism called countercurrent exchange, in which blood and water flow in discrete pathways and opposite directions. This allows gills to more efficiently extract oxygen from water and expel carbondioxide into the water. Certain details of gill anatomy differ among different species.
  5. Lungs. Terrestrial vertebrates use this method. Lungs are special organs in the body cavity that are composed of many small chambers impregnated with blood capillaries. After air enters the lungs, oxygen diffuses into the blood stream through the walls of these capillaries. It then moves from the lung capillaries to the different muscles and organs of the body. Humans and other mammals have lungs in which air moves in and out through the same pathway. In contrast, birds have more specialized lungs which use a mechanism called cross-current exchange. Like the countercurrent exchange mechanism of gills, air flows through the crosscurrent exchange system of bird lungs in one direction only, making for more efficient oxygen exchange.
Respiration - Internal Respiration [next]

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

over 7 years ago

thank you i are very hapy you are so wonderfull. i now understand engrish and this place help alot

Vote down Vote up

29 days ago

tank ou i very hapy aslo. ou much nise. me luv ou

Vote down Vote up

3 months ago

spring. I love http://www.ray-ban-outlet.us.com/ April, just http://www.bcbg-dresses.com/ warm, there http://www.michael--kors.us.com/ is an http://www.burberryonlineshop.de/ infinite http://www.gucci-shoes.net/ poetic http://www.nikestore.us/ heart. Nothing http://www.yogapantscanada.ca/ else http://monsterbeats.co-om.com/ and enjoy a few http://www.polo-outlets.com.co/ bundles http://www.oakleysunglasses-cheap.in.net/ safflower, http://www.michaeljordan.com.de/ see http://www.nike-air-max.com.de/ a http://www.tiffanyandco-canada.ca/ few http://www.nike-airmaxinc.co.uk/ green http://www.asics-outlet.us.com/ leaves. http://www.newbalance-outlet.org/ Marching http://grizzlies.nbajersey.us.com/ cloud http://www.pandora.com.de/ footprint, http://www.swarovskijewelry.com.co/ holding wind http://www.coach-factoryoutlet.net.co/ elegant, romantic http://www.giuseppezanotti.com.co/ look for http://www.nike-maxfr.com/ earth, pleasant taste and http://www.cheap-raybans.com/ meticulous scene, http://heat.nbajersey.us.com/ pavilions http://www.juicycouture.com.co/ seek rhyme http://www.nikeair-max.es/ style, http://www.beatsbydre.com.co/ hazy http://www.longchampoutlet.com.co/ look http://www.lululemon-australia.com.au/ for http://76ers.nbajersey.us.com/ warm memories. http://www.bcbg-maxazria.ca/ In http://www.michaelkors.so/ April, http://www.vans-schuhe.com.de/ stretch http://www.oakley-outletstore.in.net/ the http://www.hermes-outlet.com.co/ fragrance, bathed http://www.beats-by-dre.com.co/ in http://www.nikerosherun.us/ a beautiful spring. Life http://coachoutlet.euro-us.net/ encounter http://hornets.nbajersey.us.com/ warmest, http://www.tiffanyand-co.net.co/ than the http://www.beatsbydrdre.co.com/ flowering season http://northfaceoutlet.co-om.com/ for http://www.toryburchoutlet-sale.us.com/ Love http://www.nike-air-force.de/ romantic youth. Xu http://www.thenorthfacejackets.net.co/ had a http://www.christianlouboutin.org.uk/ dream, http://www.christian-louboutinshoes.com.co/ a http://www.yoga-pants.net.co/ dream http://www.ghd-hairstraightener.net/ of http://www.nfl-jersey.us.com/ you as I http://www.swarovski-crystal.us.com/ hold an http://www.truereligionjeans.net.co/ umbrella, if http://www.michaelkorsoutletonline-sale.us.com/ not with http://www.tommy-hilfigeroutlet.com/ an umbrella, http://www.longchamp.com.de/ and I wish you rain http://www.michaelkors-outlet-online.com.co/ together, in http://www.rolexwatches-canada.ca/ the cold world http://www.oakleyoutlet-online.us.com/ planted http://www.cheapmichaelkors.us.org/ a touch http://www.northfaceoutlet.com.co/ of http://www.nikefree5.net/ sadness. In http://www.replica-handbags.net.co/ fact, similar http://www.poloralphlaurenoutlet.net.co/ to http://www.prada-shoes.com.co/ the http://www.swarovski-online-shop.de/ Red, so there will http://www.ralphlaurenoutletonline.us.org/ always be a http://clippers.nbajersey.us.com/ man, http://www.guccishoes.in.net/ sooner http://www.gucci-outletstore.com/ or later http://www.longchamps.us.com/ will be http://www.soccer-shoesoutlet.com/ admitted http://www.lauren-ralph.co.uk/ to each http://www.christian--louboutin.in.net/ other's heart, http://www.nikefree-run.net/ the heart can http://www.burberry-outletonlinesale.in.net/ be http://www.pandoracharms-canada.ca/ deposited romantic sea waves. http://www.cheap-oakleyglasses.us.com/ In http://www.michaelkors-canadaoutlet.ca/ April, http://www.mcmhandbags.com.co/ more http://pelicans.nbajersey.us.com/ than the http://www.omega-watches.us.com/ arrival http://www.christianlouboutinoutlet.net.co/ of spring, http://www.salomon-schuhe.com.de/ there http://www.cheap-nike-shoes.net/ are http://www.pumaonline-shop.de/ flowers. http://www.ugg-australia.com.de/ After some time, http://www.guccishoes.com.co/ the http://www.retro-jordans.com/ roses http://www.toms-shoesoutlet.net/ bloom. http://www.thenorthface.com.de/ I do not http://www.adidas-superstar.nl/ think http://www.lululemoncanada.ca/ the http://www.ferragamo.com.co/ arrival of another http://www.nike-skor.com.se/ passionately http://www.coachblackfriday.com/ blooming, http://www.ralphlaurenoutlet-online.us.com/ and http://www.burberry-bagsoutlet.com/ so http://www.mizuno-running.net/ long as http://www.uggs-onsale.net/ the rose. Rose http://www.replicarolex-watches.us.com/ Bloom is http://www.outlet-burberry.net.co/ an http://www.tomsoutletonline.net/ indulgence, but also http://www.uggs.in.net/ a http://www.uhren-shop.com.de/ loose, http://www.uggboots.com.de/ open is a http://www.burberryoutlet-sale.in.net/ an event. April http://www.ugg-uggboots.net/ is http://www.thejoreseproject.com/ good, http://www.hollister-clothing.in.net/ do not http://www.pandora-charms.org.uk/ bother http://www.ralphslauren-outlet.co.uk/ to http://www.airmax-90.org/ feel, and need http://www.adidas.org.es/ to http://www.burberry2016.co.uk/ catch http://www.supra-shoes.org/ up http://www.adidasshoescanada.ca/ in full http://www.michaelkorsoutlet.ar.com/ swing, http://www.burberry-outletcanada.ca/ as long as http://www.hollisters-canada.ca/ in normal http://www.nikeair-max.ca/ days, mild http://www.oakley-sunglasses.mex.com/ air filled, occasionally calling http://www.coco-chanel.com.de/ for rain, http://www.salvatoreferragamo.in.net/ water http://www.prada.com.de/ was full of http://www.toms-outlets.us.com/ poetic, http://www.tommyhilfiger.net.co/ it http://www.weddingdressessonline.ca/ makes http://www.kate-spade.in.net/ me http://www.tommy-hilfiger.com.de/ a http://www.tommyhilfigerca.ca/ light, http://knicks.nbajersey.us.com/ which http://www.nike-shoescanada.ca/ is http://www.abercrombiefitchs.us.com/ quiet http://www.gucci-taschen-outlet.de/ no April http://www.tiffany-andco.com.au/ sound http://www.michaelkors.com.se/ beautiful. In April, http://www.pandorajewelry.top/ the http://rockets.nbajersey.us.com/ beautiful landscape, http://www.rayban.co.nl/ Tian Mei love. http://www.tommyhilfigeroutlet.in.net/ Carrying fragrant April, http://www.hollister-abercrombie.com.se/ quietly savor http://bucks.nbajersey.us.com/ a http://www.truereligion-outlet.com.co/ tree flowers, http://www.newbalancecanada.ca/ listening http://www.nikemercurial.in.net/ to the http://www.new-balance-schuhe.de/ whisper http://www.coachoutlet-online.com.co/ whisper swallow, http://www.jordan-shoes.com.co/ taste http://www.woolrich-clearance.com/ the breath http://www.harrods-london.co.uk/ of http://www.tory-burchshoesoutlet.net/ spring, there http://www.levisjeans.com.co/ is http://www.toryburchsale.com.co/ hope, http://www.nike-schuhe.com.de/ there http://www.reebok.com.de/ is vision, cut a http://www.guccioutlet-sale.in.net/ river http://www.tomsoutlet-online.com/ flows, http://www.tommy-hilfiger.co.nl/ a pulse v feelings, http://www.giuseppe-zanotti.net/ cemented timeless landscape, http://kings.nbajersey.us.com/ also http://www.rayban-wayfarer.in.net/ there http://www.pulseras-pandora.com.es/ is love http://www.chanelhandbags.net.in/ in the http://www.katespadeoutlet.gb.net/ world http://www.pradahandbags.net.co/ gazing http://www.jordanrelease-dates.us.com/ fragrant. http://www.toms-shoes.net.co/ In http://celtics.nbajersey.us.com/ April http://www.toryburch-sandals.in.net/ door, the chimes http://www.beats-headphone.com.co/ rang miss, http://uggboots.misblackfriday.com/ the http://www.ralphlaurenpolos.in.net/ memory http://www.oakleysunglasses-canada.ca/ still http://www.jimmy-choos.com/ playing http://www.burberry-handbags2016.in.net/ the http://www.montblanc--pens.in.net/ happy http://www.adidas-superstar.de/ note. http://www.nikefactory.org/ A cup of tea, a book, http://www.insanity-workout.us.com/ flowers, Yang http://www.air-huarache.co.uk/ Liu http://www.nike-schoenen.co.nl/ Hanyan, http://www.nike-free-run.de/ quiet http://www.converse-shoes.net/ and elegant, http://www.mkoutletonline.us.com/ bearing http://www.hogan.com.de/ extraordinary. http://mcmbackpack.co-om.com/ Do http://www.canadagooses-2016.com/ not http://www.mmoncler-outlet.com/ seek fame and http://www.nike-air-max.us/ wealth stay, http://www.eyeglassframes.in.net/ unperturbed http://thunder.nbajersey.us.com/ owned http://www.newbalance.com.es/ Zen. http://www.cheapuggboots.us.com/ Window beautiful spring flowers http://www.nikeshoesoutlet.org.uk/ field; gurgling http://www.rolexwatchesforsale.us.com/ brook, http://www.michael-kors-taschen.com.de/ singing http://www.guccihandbags.net.co/ with http://www.designerhandbagsoutlet.net.co/ running http://www.replica-watches.com.co/ away. Occasionally http://www.prada-handbags.com.co/ swim http://www.basketballshoes.com.co/ to http://www.uggboots.net.co/ a http://www.swarovski-australia.com.au/ group http://www.bottegaveneta-bagsoutlet.com/ of ducks, http://nuggets.nbajersey.us.com/ rattle http://lakers.nbajersey.us.com/ Huan calls, frolic with green waters. http://www.hollisterclothingstore.org/ Farming April day, http://www.weddingdressesuk.org.uk/ everywhere is http://www.burberry-outletstore.net/ a http://michaelkors.euro-us.net/ busy scene, Guyu before, http://www.timberlandshoes.net.co/ melons http://www.cheaprayban.com.co/ points beans, http://www.toms--outlet.com.co/ there http://www.uggsaustralia.com.co/ are flat http://www.kate-spade.gb.net/ line http://www.ralphlauren-polos.co.uk/ spacing, fertilization, http://www.converse.net.co/ hunched http://www.michael-kors-outlet.us.org/ lost http://www.zxcoachoutlet.com/ species, the http://www.celine-bags.org/ joy http://www.tiffany-jewelry.net/ of http://www.coachhandbags2016.us.com/ his http://www.nike-air-max.com.au/ face http://www.jordanretro.org/ that http://www.soft-ballbats.com/ says http://www.michael-kors.com.co/ harvest expectations! http://timberwolves.nbajersey.us.com/ The http://www.scarpe-hoganoutlets.it/ more http://www.newbalance-shoes.org/ time older http://www.rayban.com.de/ people more light. http://www.michaelkors.co.nl/ After http://www.christianlouboutin-shoes.ca/ years http://www.pumashoes.in.net/ of http://www.the-northface.com.co/ temper, things subjected http://trailblazers.nbajersey.us.com/ to http://www.coach-factory.in.net/ tie him down, perhaps http://www.ralph-laurens.org.uk/ a http://www.burberrys-outlet.co.uk/ heart is http://www.michael-kors-australia.com.au/ no http://www.thenorth-face.ca/ longer young, http://www.canada-goosesjackets.us.com/ once http://warriors.nbajersey.us.com/ surging, already http://www.rayban.org.es/ become http://www.michael-korshandbags.org.uk/ Delicate thin clouds. Habit http://www.coachoutletstore.net.co/ of http://www.nike-shoesoutlet.us.com/ swaying http://www.ralphlaurenepolo.com/ lights http://www.burberrys-outlet2016.com/ at http://www.cheapshoes.com.co/ night, http://www.rolex-watches.us.com/ the http://www.ugg-boots.ca/ old http://www.mcm-backpacks.com/ window http://www.chiflatiron.net.co/ to perform http://www.burberry-handbagsoutlet.com.co/ a http://www.guccishoes-uk.co.uk/ so http://www.oakley.org.es/ small print, ze http://coach.euro-us.net/ wish to http://www.thomas-sabos.org.uk/ write http://nike.shoesoutlet.us.com/ to http://www.ray-banocchiali.it/ their http://www.nikeskos.dk/ emotions quietly http://www.ray-bansunglasses.net/ placed http://cavaliers.nbajersey.us.com/ words. The http://www.swarovski-canada.ca/ more http://www.tocoachoutlet.com/ traveled road, http://www.longchamp.com.co/ you just do http://www.uggs.co.nl/ not http://www.nikeair--max.fr/ think http://www.nbajersey.us.com/ long; http://www.nikefree-run.org.uk/ more http://www.vans-shoes.net/ tours over http://wizards.nbajersey.us.com/ the http://www.ralphs-lauren.co.uk/ landscape, you http://www.handbagsoutlet.net.co/ just http://www.babyliss-pro.us.com/ do http://airmax.shoesoutlet.us.com/ not http://www.oakley--sunglasses.com.au/ feel sad. Time flies http://www.ugg-bootsclearance.com/ when, http://www.oakleys-sunglasses.us.com/ once http://www.abercrombie-kid.us.com/ again http://www.tomsshoes-outlet.us.com/ the http://pistons.nbajersey.us.com/ heart of http://www.montres-pascher.fr/ the sea waves, a http://www.rolex-watch.me.uk/ heart can http://www.raybans-sunglassesoutlet.in.net/ calm http://www.tommy-hilfiger-online-shop.de/ down, http://www.tnf-jackets.us.com/ will still http://www.abercrombie-hollister.nl/ light http://www.iphone-cases.net.co/ pull http://www.chanel-bags.com.co/ Yuet http://www.coachoutletstore-online.com.co/ Wah, on the http://www.airjordans.us/ film http://www.oakleys-glasses.us.com/ pairs. http://www.rosherun.org.uk/ Idle http://www.michaelkorsbags.us.org/ words, http://www.oakley.com.de/ with http://www.truereligion-outlet.us.org/ the http://www.asicsgels.de/ most sincere feelings http://www.ralphlaurenoutlet-online.in.net/ for http://www.omegarelojes.es/ you http://www.true-religion.com.co/ to write the http://www.soccer-shoes.us.com/ most http://supra.shoesoutlet.us.com/ beautiful http://www.mcm-bags.us.com/ verse. http://bulls.nbajersey.us.com/ Dreaming Seamless, life http://www.michael-kors-outlet-online.us.org/ is http://suns.nbajersey.us.com/ a http://www.coach-outletonline.net.co/ dream. Edge to http://www.p90xworkout.us.com/ edge http://www.hermesbags.jp.net/ to http://www.cheap-michaelkors.com/ edge of http://www.juicycoutureoutlet.net.co/ the http://www.nike--freerun.co.uk/ water, quiet http://raptors.nbajersey.us.com/ message to dream http://www.the-northface.net.co/ landscapes rhyme, taste http://www.ugg-boots-australia.com.au/ Shochiku http://www.michaelkors-uk.org.uk/ often http://www.michael-kors.net.co/ think http://www.bebeclothing.in.net/ of http://www.longchamphandbagsoutlet.net/ quiet, http://www.ralphlauren-polos.com.co/ the http://spurs.nbajersey.us.com/ wind http://www.michaelkorsoutlet-online.ar.com/ Yi companion mundane. And http://www.polos-ralphlauren.us.com/ rest in http://www.tiffany-und-co.de/ April, http://www.barbour-jacketsoutlet.com/ fragrant, http://www.ugg-boots.us.org/ quiet calm http://www.airmax-2015.org/ from http://www.ralph-lauren.com.au/ leisurely. Cantabile http://www.mk-outlet.us.com/ April, http://www.christianlouboutinshoesoutlet.org/ loaded http://www.converse.com.de/ with http://www.coach-purseoutlet.net/ poetic http://www.michael-kors-handbags.us.com/ Love, may the http://www.fashionclothes.us.com/ years http://www.converses-outlet.com/ of quiet http://www.cheapjerseys.com.co/ good, http://www.ralphlaurenonlineshop.de/ heart from http://www.horloges-rolex.nl/ Midsummer http://magic.nbajersey.us.com/ night, I stood in http://www.nike-air-max.com.se/ the http://www.mcmbags.us.com/ garden http://www.chi-flatiron.us.com/ of flowerbeds being. Front Blossoms scene, a http://hawks.nbajersey.us.com/ hundred thousand http://www.nike-roshe-run.de/ Jiao http://www.thenorth-faces.co.uk/ Mei. http://www.burberryoutlet2016.us.com/ In http://www.timberlands-paschere.fr/ that http://www.nike-rosherun.nl/ Hidee http://airhuarache.shoesoutlet.us.com/ Painting http://www.oakleysunglass-outlet.net/ graceful vine on http://www.mcm-handbags.org/ soft, http://www.edhardy.us.org/ shy Turui http://www.newoutletonlinemall.com/ aromatic flowers http://www.cheapoakley-sunglasses.com/ bursts http://www.raybans.us.org/ Descent http://www.pradaoutlet.com.co/ of Wanxiang, intoxicating air of http://www.raybanoutlet.ca/ Zinfandel http://pacers.nbajersey.us.com/ seduce the http://www.instylers.us.com/ human http://www.adidasshoes.top/ soul, http://nets.nbajersey.us.com/ I http://www.nike.org.es/ do not know http://www.longchamp-bags.us.com/ how http://www.coach-factoryyoutletonline.net/ many http://www.swarovski--uk.me.uk/ deeply http://airmax.misblackfriday.com/ moved http://www.ralphlauren-outlet.ca/ at the http://www.christianlouboutinshoes.jp.net/ child's feelings. But http://www.hollisterclothes.us.com/ this time, http://www.thomas-sabo.com.de/ it's http://jazz.nbajersey.us.com/ never http://www.oakleyoutlet.ar.com/ hard to see http://www.hollisteronlineshop.com.de/ Plum Fang-shadows. http://www.jimmy-chooshoes.com/ I know http://www.michael-kors.com.es/ that http://www.nikestore.com.de/ in http://www.longchamp-handbagsoutlet.us.com/ this midsummer find http://www.polo-ralph-lauren.de/ plum, good Yisi http://www.nike-roshe-run.com.es/ mortal http://www.hermesbirkin-bag.net/ pretenders http://www.calvin-kleins.us.com/ Yaotai http://www.uggsoutlet.com.co/ Regard. Nevertheless, http://mavericks.nbajersey.us.com/ plum http://www.abercrombie-fitchsale.com/ glamorous, sentiments http://www.cheapjerseys.us.org/ and http://www.cheap-jordans.net/ style are http://www.maccosmetics.gr.com/ forever http://www.valentino-shoesoutlet.us.com/ embedded in http://www.adidas-schuhe-online.de/ my http://www.marc-jacobs.us.com/ mind, http://www.barbour-factory.com/ any http://www.designer-handbagsoutlet.us.com/ mountain http://www.tiffany-andco.us.com/ thunder, fire http://www.rosheruns.us/ and waves, not withered http://www.marcjacobs.us.com/ and http://www.air-max.com.de/ dying http://www.pandorajewellery.com.au/ in http://www.abercrombie-andfitch.ca/ my http://www.nike-tnrequinpascher.fr/ heart, my http://www.bottega-veneta.us.com/ heart God http://www.abercrombie-and-fitch.us.com/ forever http://www.cheap-baseballbats.net/ cast bottom blossoming plum Fanghun http://michaelkors.co-om.com/ shadows. http://www.lululemonoutlet.gb.net/ Therefore, in http://www.coco-chanels.us.com/ this http://www.moncler-outlet.us.org/ June, she http://www.cheapoakley-sunglasses.in.net/ explains, http://www.ralphlaurenoutlet.us.com/ in http://www.eyeglassesonline.us.com/ this http://www.maccosmetics.net.co/ group http://www.timberlandbootsoutlet.us.com/ of http://www.the-northfacejackets.us.com/ brilliant pink http://www.rayban-sunglasses.us.org/ team http://www.burberry-outlet.net.co/ being, http://www.adidas.com.se/ I want to pull http://www.vans-shoes.co.uk/ offering http://www.rayban-sunglassesoutlet.co.uk/ plum, plum http://www.ferragamoshoes.in.net/ pondering soul. http://www.nike-huarache.nl/ "Marie http://www.toms-shoes.com.co/ has http://www.airhuarache.co.uk/ beauty, http://www.polooutlets-store.com/

http://www.ghdhair-straighteners.co.uk/

Vote down Vote up

about 1 year ago

Thank u for the info :)
i needed it to prepare for my demo lecture..