bio unit 3 (goes through all topics)

revision :)

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  • Created by: bethh
  • Created on: 15-05-09 15:48

topic 1, movement of dissolved substances

  • Diffusion
  • Osmosis
  • Active Transport


Random movement of particals results is particles 'spreading out' diffusing along a concentration gradient (from areas of high concentration to low concentraion)


only water -moves through a partialy permiable membrane from high concentration (of water) to low concentration.

Active transport

moves AGAINST the concentratin gradient. (form low concentration to high concentration)

needs (from respireation)energy to do this and respiration incereases active transport can increase

EG, in the intestines diffusion to get most sugars across but then when there is a higher concentration on the other side it uses active transoport to get the rest across

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excange of substances and adaptations, eg in the a

gas excange in alvioli

  • very thin walls makes diffusion easy
  • moist surface disolves the gasses which makes it easy
  • good blood supply keeps strong concentration gradient
  • large surface area, more area for gasses to dissolve across

1. Oxgyen goes into blood by diffusion

2. Carbon dioxide leaves blood by diffusion

Exchange of substannces in the gut

Villi - rich blood supply=steep concentration gradient=more efficient

- large SA

- thin wall (only 1 cell thick)

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digestion and absorption

your body needs the digested food to get into the blood stream

this happens by diffusion and active transport

the digested food molcules are initally higher in concentration in the intestine than in the blood, so the particles diffuse into the blood

when most food has digested there is no concentration gradient so no more can diffuse. So, the remaining food is moved across by active transport.

the body dose this because the energy it gets from the extra food transfered across is far greater than what it uses for the active transport of it

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