Question

Compare and contrast facilitated diffusion primary active transport and secondary active transport

Answer 1

Answer: 1. Facilitated diffusion: As the name suggests this type of diffusion is facilitated or let's say supported by a glycoprotein channel. This channels can be specific for the transport of certain molecules across them such as GLUT transporters for the passage of glucose. In this type of diffusion, solute moves from high to low concentration i.e. the solute will move from place A (at high conc) to place B (at low conc). So for example, if glucose is present in high concentration in blood it will move from the blood into the cells which have a relatively low concentration of glucose. This is also a uniport mode of transport.
2. Primary active transport: In this type of transport solute moves against the concentration gradient and so it requires energy which is provided in the form of ATP. Let's consider the example of sodium/potassium ATPase pump which moves sodium out of the cell and potassium is brought inside the cell which is energetically less favorable because sodium ion concentration is already high outside the cell and vice versa for potassium ion. Hence, ATP is utilized to overcome the barrier as against what happens in facilitated diffusion where movement of ions is along the concentration gradient.
3. Secondary active transport: This type of transport allows movement of two molecules simultaneously where one molecule travel along the concentration gradient and another molecule travels against the concentration gradient but both of them move in the same direction (symport) or when they move in opposite direction (antiport). This is different from facilitated diffusion since the movement of one of the ion is against the concentration gradient and different from primary active transport in that it is not utilizing cellular energy and it facilitates movement of two molecules simultaneously.