Movement of Substances Across Cell Membranes in the Functioning of Cells Tissues and Organs

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There are many ways in which substances can move across the cell membrane and in which then helps in the function of the body (cells, tissues and organs) overall. There are 3 processes that a substance can move across the membrane, theses are diffusion (simple and facilitated), osmosis and active transport. Both diffusion and osmosis are passive processes, which mean they do not need energy to occur, whereas active transport does require energy. All three processes are involved in many functions of the body, including photosynthesis and respiration and gas exchange in a fish.

The structure of the cell membrane is important in the movement of the substances. It has structure which is referred to as the ‘fluid mosaic model’. This is when the membrane consists of two layers of phospholipid molecules. Proteins are embedded in each thin layer of phospholipids, some span the membrane from one side to the other, and others appear on one face of the membrane only. The proteins that span the membrane, called intrinsic proteins, are the ones that are important in the transport of substances across the membrane. The phospholipids join together and make a phospholipid bilayer.

One process in which water can move across membranes is osmosis. This is a process that involves the passive moment of water molecules through a partially permeable membrane from an area of high water concentration to an area of low water concentration. It does not require any energy to take place as it works on a concentration gradient. For cells to survive, ion concentration needs to be the same on both sides of the membrane. If the cell does not pump out all of its extra ions to even out the concentrations, the water is going to move in. This can be very bad as the cells can swell up and explode. Osmosis is a very useful process in the plant as it insures that the cells in the plant are turgid, swollen and hard, this turgidity is important as it makes the plant stand up to the sun light....
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