Question

Facilitated diffusion differs from diffusion in that facilitated diffusion a. involves the passive use of a carrier protein. b. involves the active use of a carrier protein. c. moves a molecule from a low to high concentration. d. involves the use of ATP molecules.

Short answer

The correct statement that differentiates facilitated diffusion from simple diffusion is option a: "involves the passive use of a carrier protein."

Step-by-step solution

Understanding facilitated diffusion and diffusion

Facilitated diffusion is a type of passive transport that helps the movement of specific molecules across cell membranes. It involves the use of integral membrane proteins called carrier proteins or channels that aid molecules in traversing the membrane. On the other hand, simple diffusion is the process by which molecules move from an area of high concentration to an area of low concentration without any assistance.

Evaluate option a - passive use of a carrier protein

In facilitated diffusion, carrier proteins or channels assist molecules in moving across the membrane, but they do not use energy in doing so—it is a passive process. Simple diffusion does not involve any carrier proteins. Thus, option a correctly identifies the difference between facilitated diffusion and simple diffusion.

Evaluate option b - active use of a carrier protein

This option implies that in facilitated diffusion, there is an energy requirement to use carrier proteins. However, facilitated diffusion is a passive process and does not use any cellular energy. Therefore, this option is incorrect.

Evaluate option c - moves a molecule from low to high concentration

This statement refers to a characteristic of active transport, wherein molecules are moved against their concentration gradients, from low to high concentrations. This process requires energy. However, this is not applicable to facilitated diffusion, which is a passive process where molecules move along their concentration gradients. Hence, option c is not correct.

Evaluate option d - involves the use of ATP molecules

The presence of ATP molecules indicates that a process requires energy to take place. Facilitated diffusion, however, is a passive process and does not require energy. Thus, option d is incorrect.

Identify the correct statement

The correct statement that differentiates facilitated diffusion from simple diffusion is option a: "involves the passive use of a carrier protein." All the other options either describe characteristics of active transport or are incorrect descriptions of facilitated diffusion.

Key concepts

Understanding Passive Transport

Passive transport is a fundamental concept in biology, referring to the movement of substances across cell membranes without the input of energy. It relies on the natural kinetic energy of molecules and progresses along the gradient of concentration, from higher to lower, a process driven by entropy.

One of the key features of passive transport is that it does not require cells to expend cellular energy in the form of adenosine triphosphate (ATP). Instead, particles diffuse through the lipid bilayer or through pores or channels in the membrane. This is a spontaneous and energy-efficient means for cells to regulate internal concentrations of various biomolecules.

Examples of passive transport include simple diffusion, osmosis (the diffusion of water molecules), and facilitated diffusion, which utilizes carrier proteins to transport substances that cannot pass through the lipid bilayer directly.

Role of Carrier Proteins in Facilitated Diffusion

Carrier proteins play a pivotal role in the process known as facilitated diffusion—a type of passive transport. These proteins are specific, integral parts of the cell membrane that bind to molecules and change shape to shuttle the molecules across the membrane.

Specificity and Saturation

Each carrier protein is designed to recognize and transport a specific molecule or ion. When the targeted substance binds to the carrier protein, the protein undergoes a conformational change. This allows the substance to be released on the other side of the membrane. Carrier proteins are limited in number; thus, they can become saturated when all are bound to molecules, meaning there's a maximum rate at which they can work.

Advantages Over Simple Diffusion

Substances that are either too large, polar, or charged for simple diffusion can still move across the cell membrane via facilitated diffusion with the help of these proteins, thus bypassing the restrictive nature of the lipid bilayer.

Cell Membrane Transport Mechanisms

The cell membrane is a dynamic barrier that regulates the movement of substances into and out of a cell. Transport across the cell membrane can occur via passive or active mechanisms depending on the energy requirements and direction of movement.

Integrating Facilitated Diffusion

In facilitated diffusion, carrier proteins and channel proteins are two types of membrane proteins involved. While carrier proteins bind to substances and aid in their transport, channel proteins form pores through which ions and small molecules can pass.

• Passive transport: Includes simple diffusion, facilitated diffusion, and osmosis.
• Active transport: Requires energy to move substances against their concentration gradient.

It's crucial for homeostasis that cells maintain a precise control of this transport, offering a harmonious exchange of essential compounds and ions while preserving the internal environment.

Navigating the Concentration Gradient

The concentration gradient is a term that describes the difference in concentration of a substance between two adjacent areas. Particles have a natural tendency to move from areas of higher concentration to areas of lower concentration, seeking to reach equilibrium.

Driving Force Behind Diffusion

These gradients are vital to various physiological processes, as they are the driving forces behind the diffusion process, whether it be simple or facilitated diffusion. For facilitated diffusion, it's pivotal that the substance moves down its concentration gradient—which means moving from a region where it is more concentrated to a region where it is less concentrated, without using cellular energy.

This fundamental principle underpins many biological processes, from the respiratory exchange of gases to the renal absorption of nutrients, highlighting the indispensable role gradients play in cellular function and overall homeostasis.