Question

Which process undergoes saturation? (a) Facilitated diffusion (b) Active transport (c) Simple diffusion (d) Both (a) and (b)

Short answer

The processes that undergo saturation are Facilitated diffusion and Active transport. So, the answer is (d) Both (a) and (b)

Step-by-step solution

Understanding Facilitated Diffusion

Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. This type of transport can become saturate when the protein carrier becomes fully occupied making it unable to transport more molecules.

Understanding Active Transport

Active transport is a process that moves molecules against a concentration gradient, from an area of lower concentration to an area of higher concentration. It is saturate and limited by the number of available carrier proteins. When all proteins are being used, the rate cannot increase even if there's more of the substance available to transport.

Understanding Simple diffusion

Simple diffusion is a passive transport process that doesn't require transport proteins. Hence, it doesn't undergo saturation as it can continue as long as the concentration gradient exists.

Key concepts

Facilitated Diffusion

Facilitated diffusion is an essential mechanism that helps transport molecules across the cell membrane. This process operates without the use of energy, as it is a type of passive transport.
Instead of energy, it relies on specialized proteins embedded in the cell membrane to move substances down their concentration gradient, from areas of higher concentration to those of lower concentration.
These proteins act like gateways, providing specific pathways for substances such as glucose and amino acids.

• The key feature of facilitated diffusion is its reliance on transport proteins, which can become saturated. This means that if all the protein carriers are occupied, the rate of diffusion will not increase, even if more molecules are present. Thus, the transport is limited by the availability of these proteins.

Active Transport

Active transport is a unique process that enables cells to move molecules against their concentration gradient, which is from areas of lower concentration to areas of higher concentration.
Unlike passive transport methods like diffusion, active transport requires energy, usually in the form of adenosine triphosphate (ATP).
This ability is crucial for maintaining cellular functions such as nutrient uptake and ion balance

• Like facilitated diffusion, active transport can become saturated. This saturation happens because there is a finite number of transport proteins in the cell membrane that can handle certain substances.
• Once all these transport proteins are occupied, the rate of transport will not increase, even if more molecules are available.

Saturation in Transport Proteins

Transport proteins have a pivotal role in both facilitated diffusion and active transport as they mediate these processes across cell membranes.
Saturation occurs when these proteins become fully occupied, meaning they cannot transport additional molecules until some of their current substrates have been moved.
This limit affects the efficiency and rate of transport, regardless of whether more molecules are available.

• The concept of saturation is important because it delineates a maximum capacity or speed for processes involving transport proteins. In situations where demand exceeds supply, this cap can lead to a queue-like scenario where molecules must "wait" for available transport proteins.

Simple Diffusion

Simple diffusion is a type of passive transport that occurs naturally without cellular energy or the aid of transport proteins. It allows molecules to spread out evenly by moving from areas of high concentration to areas of low concentration.
This spontaneous movement results from the random motion of molecules and is driven by their kinetic energy.

• A significant aspect of simple diffusion is that it does not undergo saturation, unlike processes involving transport proteins. Since it doesn’t rely on specific passageways or carriers, the rate of diffusion is only limited by the concentration gradient across the membrane.
• Examples of substances that commonly move by simple diffusion include oxygen, carbon dioxide, and small nonpolar molecules.