MOVEMENT ACROSS THE CELL MEMBRANE

Today, we will discuss the various types of movements across the cell membrane. This is a very important topic that you should know very well for the test. Don't just memorize the definitions but know different applications of the concepts. It is important to know some of the examples of hand!

Movement of substances across the cell membrane

1. Diffusion or passive transport: It is the movement of materials from a region of higher to a region of lower substance concentration.                                                                                                                                                                                                                                         Examples: When a bottle of perfume is opened, the scent spreads throughout the room. A drop of ink placed in a cup of water spreads throughout the water by diffusion.                                                
2. Active transport: It is the movement of molecules from a region of lower concentration to a region of higher concentration in which energy is needed in the form of ATP. The movement of the substance is against a concentration gradient.                                                                                                                                                                                                                                                          Examples: Sodium is pumped out of the cell by active diffusion. Potassium is pumped into the cell by active diffusion.                                                                                                                                       
3. Osmosis: It is the flow of water molecules from a less concentrated solution (hypotonic solution) to a higher concentrated solution (hypertonic solution) through a semi-permeable membrane.                                                                                                                                                                Example: When a red blood cell is placed into water, the water flows across the cell membrane into the cell because of the dissolved salts in the cytoplasm.                                                              Water flows from the soil into the roots of plants by osmosis.                                                                   
4. Facilitated diffusion: As certain substances move into the cell by simple or passive diffusion, they create the opportunity for other substances to go into the cell freely.                                                                                                                                                                                              Example: Glucose follows sodium as it enters the cell by facilitated diffusion.                                               
5. Endocytosis: This is the process by which the cell engulfs or captures substances into the cytoplasm. It consist of pinocytosis (Cell-drinking) and phagocytosis (Cell-eating)                                                            
6. Exocytosis: This the process by which the cell extrudes or gets rid of substances  from within the cell to the outside.