Diffusion

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  • Molecules on the move - Diffusion
    • Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration.
      • Diffusion happens in both solutions and gases because the particles in these substances are free to move about randomly.
        • The bigger the concentration gradient (the difference in concentration) the faster the diffusion rate
          • A higher temperature will also give a faster diffusion rate because the particles have more energy, so move around faster.
    • Factors affecting diffusion
      • The bigger the concentration gradient (the difference in concentration) the faster the diffusion rate
        • A higher temperature will also give a faster diffusion rate because the particles have more energy, so move around faster.
    • Cell membranes
      • They hold the cell together but they let stuff in and out as well.
        • Dissolved substances can move in and out by diffusion.
          • Only very small molecules can diffuse through cell membranes such as oxygen, glucose, amino acids and water.
          • Big molecules like starch and proteins can't fit through the membrane.
      • Particles flow through the cell membrane from where there's an area of high to low concentration
        • They only move about randomly so they go both ways - but if there's more on one side of the membrane there's a net movement from that side.
          • The higher the surface area of the membrane, the faster the diffusion rate, because more particles can pass through at once.
            • Factors affecting diffusion
    • Question - A student adds a drop of ink to a glass of cold water. A. what will the student observe to happen to the drop of ink, B. How might the observation differ if the ink was added to a glass of warm water?
      • A.The ink will diffuse and spread out through the water. This is because the ink particles will move from where is a higher concentration of them (the drop of ink) to where there is a lower concentration of them (the surrounding water).
        • B. The ink particles will diffuse/spread out faster.

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