B3- exchange of materials

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  • osmosis is the net movement of a substance down a concentration gradient over a partially permeable membrane
  • osmosis requires energy from the cell
  • only small enough particles can diffuse through the partially permeable membrane

active transport

  • active transport allows sells to take substances in against the concentration gradient- from an area of low concentration to high concentration
  • this requires more energy created by respiration than osmosis
  • cells may sometimes need to absorb substances in short supply and the transport proteins allow this
  • cells can aborb ions from dilute substances e.g a root hair cell can absorb nitrates from soil water
  • glucose is absorbed by the kidney through active transport
  • the transport protein takes the useful molecule and turns into the cell then releases using energy

sports drink dilemma

  • when you exercise your muscles respire to create energy for movement- glucose is used in respiration
  • when you get hot you sweat to cool down and in your sweat there is mineral ions and water- increased sweating means dehydration
  • therefore when exercising you need to replace the stuff thats lost
  • sports drinks contain sugar, water and mineral ions designed to rehydrate the body cells
  • if a drink concentration matches the body fluid it is isotonic

exchanging materials in the lungs

  • large, complex organisms have large surface areas to obtain food and oxygen thats needed
  • soluble food is absorbed by the small intestine, oxygen by the lungs and co2 is removed from them
  • efficient exchange surface- thin walls for diffusion, large SA and an efficient transport system (circulatory system)
  • in the lungs there is a gaseous exhchange surface (exchange of oxygen and co2 between the air in lungs and blood) the surface area is increased by the multiple alveoli which are air sacs
  • the lungs are ventilated…


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