Exchange and Transport

Notes on exchange surfaces in general, how gasses get into plants, insects and fish.

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  • Created by: luce
  • Created on: 06-05-09 14:17

Exchange between organisms and their enviroment

Things that need to be exchanged are;

  • respiratory gases eg. oxygen carbon dioxide.
  • Nutrients eg.glucose, amino acids,vitamins and minerals
  • excretory products
  • Heat

The exchange can take place ethier passively (no energy )or actively (energy needed).

Large surface area to volume ratio to make the exchange efficient across surface. For example the lungs have a large surface area with the aveoli.

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Features of specialised exchange surfaces

  • Large surface area to volume ratio - increases rate of exchange
  • vary thin so that the diffusion distance is short - material cross rapidly
  • partially pearmeable
  • movement of enviromental medium eg air - to maintain a steep diffusion gradient
  • movement of internal medium eg blood - maintains steep diffusion gradient.

Often the exchange surfaces are located inside the organism as they can be easily damaged.

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Single celled organisms and Insects

Single celled organisms are small so have large surface area to volume ratio. oxygen is absorbed by diffusion and carbon dioxide diffuses out in the same way.

Many spiricales on surface of insect

tubes called tracheae - smaller tubes called tracheoles.

gases move in and out along the diffusion gradient. the insect can move spiricles open and closed, further speeding up the process - ventilation.

spricles often closed to conserve water but can open so water can evaporate.

the system limits the size an insect can be as there needs to be a short diffusion pathway out of the insect.

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Gas exchange in fish!


located behind the head.

gas exchange happens in the gills which are made up of gill filaments.

Gill lamellae furthermore increase the surface area of the gill making it more efficient.

the blood flow are water flow happens in oppisite direction. this is called the countercurrent flow.

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Countercurrent Exchange - explained

  • The blood and the water flow over the gill lamellae in oppisite directions.

Blood (with a low Concentration of oxygen) meets the water (high in oxygen) This way, diffusion of oxygen takes place.

The water this way always has a higher concentraion of oxygen than the blood so diffusion of gasses always happens.

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