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Consider the main processes in which substances pass through the plasma membrane.

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Introduction

There are many ways in which different substances can move in and out of the plasma membrane of a cell. A reason for the movement of substances in and out of cells is the structure of the cell membrane, which is about 7nm thick and is made of a phospholipid bilayer that allows molecules to pass. I am going to consider the main processes in which substances pass through the plasma membrane. Firstly, I will look at simple diffusion. Diffusion is the random movement of particles in a gas or liquid down a concentration gradient from a region of high concentration to low concentration*. This is the primary method by which substances are transported. The molecules are soluble in lipids and diffuse through the membrane when they collide into its bilayer. ...read more.

Middle

The way by which water molecules are diffused is called Osmosis (through a semi-permeable membrane). A semi-permeable membrane allows the molecules of water to pass through, but does not allow other molecules to be diffused through it. Osmosis enables water molecules to diffuse from a region of high water potential to a region of low water potential. Water potential is the pressure that water molecules exert when they collide into the membrane. If water potential is high, it means there is a high volume of water molecules in that region. However if the water potential is low it would mean that there are not many water molecules in that particular area. Water potential is measured in Pascals (Pa). When solute is added to the solution, the water potential decreases and so the number will be negative. ...read more.

Conclusion

A vesicle is like a sac that holds the material. The formation and movement of the vesicles is called cytosis. Therefore, exocytosis is the outward movement of products and endocytosis is the inward movement. There are two types of endocytosis: Phagocytosis - means 'cell eating'. It is the taking up of solid objects, Pinocytosis - means 'cell drinking'. It is the taking up of liquids. During exocytosis, the substance to be removed from the cell is contained in a vesicle that is usually made in the Golgi body. The Golgi releases the vesicle and it moves towards the surface of the membrane where it fuses with it. It is then released outside of the membrane. In conclusion, I can say that there are many ways in which molecules can enter and exit a cell through a plasma membrane, some of which also involve other organelles such as the Golgi body. 1 ...read more.

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