Vocabulary: active transport, cell membrane, diffusion, digestion, passive transport
The cell membrane or plasma membrane performs a number of important functions for the cell. These functions include the separation of the cell from its outside environment, controlling which molecules enter and leave the cell, and recognition of chemical signals. The cell membrane consists of two layers of phospholipids with proteins embedded within these layers. The surface of the cell contains molecules which recognize other molecules which may attach to or enter the cell.
Cell Membrane Structure
The processes of diffusion and active transport are important in the movement of materials in and out of cells.
Diffusion or passive transport is the movement of materials from a region of higher to a region of lower substance concentration. The diagram at the right shows the movement of molecules from higher concentration on side A to a lower concentration on side B.
In active transport, molecules move from a region of lower concentration to a region of higher concentration. As this process does not naturally occur, the cell has to use energy in the form of ATP to make active transport occur.
Many organic and inorganic substances dissolved in cells allow necessary chemical reactions to take place in order to maintain life. Large organic food molecules such as proteins and starches must initially be broken down through the life process of digestion in order to enter cells.
Organic Molecules and Digestive End Products
Digestive End Product(s) carbohydrates simple sugars (glucose) proteins amino acids lipids (fats) fatty acids and glycerol
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