Cell and Membrane Transport: Passive and Active Transport Concepts PDF

# Cell and Membrane Transport ## Membrane Transport The image shows a diagram of membrane transport with the following key aspects * **Types of Transport**: Passive and Active. Passive is further divided into Simple and Facilitated diffusion. Active is further divided into primary and secondary ac...

# Cell and Membrane Transport ## Membrane Transport The image shows a diagram of membrane transport with the following key aspects * **Types of Transport**: Passive and Active. Passive is further divided into Simple and Facilitated diffusion. Active is further divided into primary and secondary active transport, Co-transport or symport and Counter transport or antiport ### Fig. 1.6: Types of membrane transport mechanism The image shows a cell membrane and an example of Uniport, Co-transport or symport, Counter transport or antiport. * **Uniport**: A single substance is moved across the membrane. * **Symport**: Two substances are moved across the membrane in the same direction. * **Antiport**: Two substances are moved across the membrane in opposite directions. ### Fig 1.7: Uniport, symport and antiport transport of substance across the cell membrane. One of the functions of the plasma membrane is to regulate the passage of a variety of small molecules across it. Biological membranes are semipermeable membranes through which certain molecules freely diffuse across membranes but the movement of the others is restricted because of size, charge or solubility. The two types of transport mechanisms are (Fig. 1.6): 1. Passive transport or passive diffusion 2. Active transport. ## Passive Transport or Passive Diffusion * Passive transport is the process by which molecules move across a membrane without energy (ATP). * The direction of passive transport is always from a region of higher concentration to one of lower concentration. There are two types of passive transport as follows: 1. Simple diffusion 2. Facilitated diffusion. ### Simple Diffusion * Lipid soluble, i.e. lipophilic molecules can pass through cell membrane, without any interaction with carrier proteins in the membrane. Such molecules will pass through membrane along the concentration gradient, i.e. from a region of higher concentration to one of lower concentration. This process is called simple diffusion. ### Facilitated Diffusion * The movement of water soluble molecules and ions across the membrane requires specific transport system. They pass through specific carrier proteins. A carrier protein binds to a specific molecule on one side of the membrane and releases it on the other side. This type of crossing the membrane is called facilitated diffusion or carrier-mediated diffusion. * An example of facilitated diffusion is the movement of glucose and most of the amino acids across the plasma membrane. * These diffusion processes are not coupled to the movement of other ions, they are known as uniport transport processes (Fig. 1.7). ## Active Transport * If a molecule moves against a concentration gradient, an external energy source is required; this movement is referred to as active transport.