Chapter 3 - Section 3.3 - Study Guide - Assess Your Learning Outcomes - Page 109: 11

Facilitated diffusion and active transport are two distinct mechanisms by which substances are transported across biological membranes. Both processes involve the use of specialized membrane proteins, but they differ in their energy requirements, direction of transport, and the types of molecules they transport. Here are the similarities and differences between facilitated diffusion and active transport: **Similarities:** 1. **Involvement of Membrane Proteins:** Both facilitated diffusion and active transport rely on specific membrane proteins to facilitate the movement of molecules across the cell membrane. These proteins act as carriers or channels. 2. **Specificity:** Both processes exhibit a degree of specificity. The transport proteins are selective and typically transport specific molecules or ions. 3. **Saturation:** Both facilitated diffusion and active transport can become saturated when all available transport proteins are occupied. Saturation limits the rate of transport. **Differences:** 1. **Energy Requirement:** - **Facilitated Diffusion:** Facilitated diffusion is a passive process, meaning it does not require energy input from the cell. It relies on the kinetic energy of molecules to move them down their concentration gradients. - **Active Transport:** Active transport is an energy-dependent process that requires the input of energy, usually in the form of adenosine triphosphate (ATP), to move molecules against their concentration gradients. 2. **Direction of Transport:** - **Facilitated Diffusion:** Facilitated diffusion always occurs in the direction of the concentration gradient. Molecules move from areas of higher concentration to areas of lower concentration. - **Active Transport:** Active transport can move molecules against their concentration gradients, from areas of lower concentration to areas of higher concentration. 3. **Types of Molecules Transported:** - **Facilitated Diffusion:** Facilitated diffusion primarily transports molecules that are polar, charged, or too large to pass through the lipid bilayer by simple diffusion. Examples include glucose, ions, and amino acids. - **Active Transport:** Active transport is often used to transport ions (e.g., sodium, potassium, calcium) and other molecules against their concentration gradients. It is particularly important for maintaining ion gradients across cell membranes. 4. **Examples in Physiology:** - **Facilitated Diffusion:** Glucose transport into cells via glucose transporters (GLUT proteins) is an example of facilitated diffusion. Glucose moves down its concentration gradient into cells. - **Active Transport:** The sodium-potassium pump (Na+/K+ pump) is a classic example of active transport. It actively pumps sodium ions out of the cell and potassium ions into the cell against their respective concentration gradients. 5. **Regulation:** - **Facilitated Diffusion:** Facilitated diffusion is typically not regulated by the cell. The rate of transport depends on the concentration gradient. - **Active Transport:** Active transport is often tightly regulated by the cell to control the movement of specific ions or molecules in response to changing physiological conditions. In summary, while both facilitated diffusion and active transport involve the use of membrane proteins to transport molecules, they differ in terms of energy requirement, direction of transport, the types of molecules they transport, and their regulation. Facilitated diffusion is passive and moves molecules down their concentration gradients, while active transport requires energy and can move molecules against their concentration gradients.

Facilitated diffusion and active transport are two distinct mechanisms by which substances are transported across biological membranes. Both processes involve the use of specialized membrane proteins, but they differ in their energy requirements, direction of transport, and the types of molecules they transport. Here are the similarities and differences between facilitated diffusion and active transport: **Similarities:** 1. **Involvement of Membrane Proteins:** Both facilitated diffusion and active transport rely on specific membrane proteins to facilitate the movement of molecules across the cell membrane. These proteins act as carriers or channels. 2. **Specificity:** Both processes exhibit a degree of specificity. The transport proteins are selective and typically transport specific molecules or ions. 3. **Saturation:** Both facilitated diffusion and active transport can become saturated when all available transport proteins are occupied. Saturation limits the rate of transport. **Differences:** 1. **Energy Requirement:** - **Facilitated Diffusion:** Facilitated diffusion is a passive process, meaning it does not require energy input from the cell. It relies on the kinetic energy of molecules to move them down their concentration gradients. - **Active Transport:** Active transport is an energy-dependent process that requires the input of energy, usually in the form of adenosine triphosphate (ATP), to move molecules against their concentration gradients. 2. **Direction of Transport:** - **Facilitated Diffusion:** Facilitated diffusion always occurs in the direction of the concentration gradient. Molecules move from areas of higher concentration to areas of lower concentration. - **Active Transport:** Active transport can move molecules against their concentration gradients, from areas of lower concentration to areas of higher concentration. 3. **Types of Molecules Transported:** - **Facilitated Diffusion:** Facilitated diffusion primarily transports molecules that are polar, charged, or too large to pass through the lipid bilayer by simple diffusion. Examples include glucose, ions, and amino acids. - **Active Transport:** Active transport is often used to transport ions (e.g., sodium, potassium, calcium) and other molecules against their concentration gradients. It is particularly important for maintaining ion gradients across cell membranes. 4. **Examples in Physiology:** - **Facilitated Diffusion:** Glucose transport into cells via glucose transporters (GLUT proteins) is an example of facilitated diffusion. Glucose moves down its concentration gradient into cells. - **Active Transport:** The sodium-potassium pump (Na+/K+ pump) is a classic example of active transport. It actively pumps sodium ions out of the cell and potassium ions into the cell against their respective concentration gradients. 5. **Regulation:** - **Facilitated Diffusion:** Facilitated diffusion is typically not regulated by the cell. The rate of transport depends on the concentration gradient. - **Active Transport:** Active transport is often tightly regulated by the cell to control the movement of specific ions or molecules in response to changing physiological conditions. In summary, while both facilitated diffusion and active transport involve the use of membrane proteins to transport molecules, they differ in terms of energy requirement, direction of transport, the types of molecules they transport, and their regulation. Facilitated diffusion is passive and moves molecules down their concentration gradients, while active transport requires energy and can move molecules against their concentration gradients.