Diffusion across a cellular membrane

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Today the students got to talk about movement across a cellular membrane.  There are 2 types of movements; Passive transport and Active transport.  We are focusing on the passive transport as the lab later in the week focuses solely on this technique.  Today we learned about diffusion, a type of passive transport.  The demonstration we used was simply skittles in water!  The water molecules bounce off the skittles, which takes off the water soluble colors of the skittles.  Around the skittles is a high concentration of the sugar and color (solutes), therefore the solute goes down a concentration gradient towards the middle of the plate (low concentration area).  Gravity plays a big part in this also, it is what pulls the solutes down the gradient to the middle of the plate!  No energy is required for this process to happen, this is the reason diffusion is known as a passive transport.   

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