Exchange of materials

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  • Exchange of materials
    • Osmosis
      • Movement of water
      • Movement of molecules is random and requires no energy from cells
      • High concentration (dilute) to a low concentration
      • Cell membrane  partially permable
    • Active transport
      • Cells use active transport to absorb substances across partially permeable membranes against the concentration gradient.
      • Requires the use of energy released in respiration
      • Cells are able to absorb ions from dilute solutions.
      • Glucose can be reabsorbed in the kidney tubules by active transport
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    • Exchanging materials- the lungs
      • Large organisms have exchange surfaces to obtain the food and oxygen they need
      • Soluble food  absorbed by the interstine
      • The lungs contain the gaseous exchange surface
        • Surface are is increased by alveoli (air sacs)
          • Alveoli have thin walls and large surface area
      • Lungs ventilated to maintain steep diffusion gradient
    • Ventilating the lungs
      • Lungs are situated in the throax, inside the rib cage and above the diaphragm
      • When we breathe in
        • The intercostal muscles contract
        • The ribcage moves up and out and the diaphragm flattens
        • Volume of throax increases
      • When we breathe out
        • Intercostal muscles of the ribcage and diaphragm  relax
        • Ribcage moves down and in and the diaphragm becomes domed
        • Volume of throax decreases
    • Exchange in plants
      • Gases diffuse in and out leaves by the stomata
      • Plants lose water vapour through stomata due to evaporation in the leaves
      • Water and mineral ions are taken up by the roots
        • Root hair cells in crease the surface area of roots for the absorption of water and mineral irons
    • Transpiration
      • The movement of the water through the plant is called transpiration steam
      • The plant could dehydrate if the rate of evaporation in the leaves is greater than the water uptake by the roots
      • The guard cells can close to prevent excessive water loss
      • Wilting can protect the leaf from excessive water loss


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