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By what process can materials move in and out of cells and how are these movements regulated?

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Q: By what process can materials move in and out of cells and how are these movements regulated? The human body is made of many different cells, each of these cells have different structures and carry out different functions to make the body work properly. So from this you can make the assumption that because the cells have different functions and structures the way that materials pass through the cell surface membrane are different to suit each process and cell. My task is to investigate the ways that cells use, to move materials in and out of the cell surface membrane and look into ways that this movement can take place. The surface of the membrane is designed to allow the passing of materials as it is partially permeable, this means that in the membrane there are pores, which allow smaller molecules through, but not the larger more solute molecules. Also the membrane has intrinsic proteins (which run through both layers of the membrane) and extrinsic proteins (which are situated on the outer layer of the membrane). These are used to transfer none soluble substances in lipids, that would not be able to filter through the partially permeable membrane. ...read more.


And diffusion is also a passive process, as the use of energy is not needed. The rate of diffusion depends on the concentration gradient, the size and nature of the different molecule and the area which the diffusion takes place. The greater the difference in concentration gradient between the two regions that the substance is diffusing across, the greater the rate of diffusion. Small molecules diffuse faster than larger ones and fat-soluble ones diffuse more rapidly through the cell membrane than water soluble ones. The larger the surface area of which diffusion takes place means there is a greater rate of diffusion, the area of the surface is increased by the introduction of villi and microvilli. Another type of diffusion is facilitated diffusion. The word facilitated means to help and this is how this process differs as it allows a quicker exchange of particles from a high concentration to a low concentration, it is also a reversible reaction depending on the levels of concentration on both sides. It is also a passive process as no energy is involved so material is moved along the concentration gradient. ...read more.


Active transport depends on glycoproteins in the surface membrane; these are called carrier proteins. The proteins take up molecules like glucose from outside of the cell membrane. The glucose molecules attach themselves to the carrier protein and ATP binds to the membrane on the outside of the cell. Because the glucose has joined to the protein a change of shape occurs, this allows the molecules to be able to go into the inside of the cell but there is no access to the ones that are still on the outside. The glucose molecules are then released into the inside of the cell this causes the protein to repeat to its original position so active transport can take place once again. From these four different examples of the transportation of materials and the movement of these in and out of cell you can see how the surface membrane is structured to allow the passing of different molecules, solvents and particles. Whether its using a passive or active processes the cell is designed to cope with the different materials it need to move through the membrane to help make our body function and work properly. Daniel Williams 03/05/07 ...read more.

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