Problem 14 - Objective Biology for NEET

Question

Which of the following transport is not highly selective? (a) Facilitated diffusion (b) Active transport (c) Simple diffusion (d) All of these

Step-by-Step Solution

Answer

The transport that is not highly selective is (c) Simple Diffusion.

Step 1: Understanding Transport Processes

Facilitated diffusion is a type of passive transport which is instigated by membrane proteins, making it highly selective. Active transport, on the other hand, is a process where cells transport molecules against a concentration gradient, which requires energy and selective protein channels. Therefore, both facilitated transport and active transport are selective.

Step 2: Understanding Simple Diffusion

Simple diffusion refers to the movement of particles from a region of high concentration to one of low concentration, without the need for energy input and without the involvement of membrane proteins. It's not selective because it allows any particles to pass as long as there is a concentration gradient.

Step 3: Selecting the Correct Option

Considering the attributes of each process, we can see that simple diffusion is not selective, while facilitated diffusion and active transport are. Therefore, the option that describes a type of transport that is not highly selective is Simple Diffusion.

Key Concepts

Simple Diffusion

Imagine yourself in a room filled with a fragrant aroma. Soon enough, without any barriers or fans, the scent uniformly spreads across the room. This is akin to simple diffusion, a fundamental transport mechanism in cellular biology that operates on a similar principle.

Simple diffusion allows for the movement of particles such as gases, lipids, or small nonpolar molecules, across the cell membrane from a region where they are in high concentration to areas where they are in low concentration. This process does not require the cell to expend energy and occurs due to the natural motion of particles, often described as moving down their concentration gradient. An example worth noting is the diffusion of oxygen from the lung alveoli into the blood. This mechanism is not highly selective because it allows molecules to pass based solely on their concentration gradients and size, not specificity.

Facilitated Diffusion

While walking through a crowded area, sometimes you need the help of a pathway or designated lane to guide you through with ease. Similarly, in the body, certain molecules require assistance to travel across cell membranes, and that's where facilitated diffusion comes in.

This process differs from simple diffusion as it involves specific proteins—either channels or carriers—to facilitate the movement of larger or polar molecules across the membrane. These membrane-bound proteins act as selective corridors; their shape and charge are matched to particular substances, allowing only certain molecules to pass through, hence the high selectivity of this process. An example is glucose entering a cell with the aid of a glucose transporter. In facilitated diffusion, substances still move down their concentration gradient and the process is driven by passive transport, meaning it does not require cellular energy.

Active Transport

Have you ever pushed a cart up a ramp? Not only does it require effort, but you also need to steer it correctly. This is reminiscent of active transport in cellular mechanisms, which involves the movement of molecules against their concentration gradient, from an area of lower concentration to higher concentration.

Such transportation is 'active' because it requires the input of energy, usually in the form of adenosine triphosphate (ATP). Consider sodium-potassium pumps in the nerve cells that maintain a differential distribution of ions essential for nerve impulse conduction. These pumps actively move sodium ions out and potassium ions into the cell against their respective concentration gradients. Also essential are the protein carriers involved in this process; they are highly selective in their action, ensuring specific ions or molecules are transported, thus maintaining a crucial aspect of a cell's environment.