Question

Cell membrane is selective permeable. This means that it (a) allows all materials to pass through (b) allows only water to pass through (c) allows only certain materials to pass through (d) allows only ions to pass through.

Short answer

The correct answer is (c) allows only certain materials to pass through.

Step-by-step solution

Understanding the Concept of Selective Permeability

Selective permeability is a property of cellular membranes that only allows certain molecules or ions to pass through it by means of active or passive transport.

Analyzing the Given Options

Analyze each option to determine which one correctly describes the property of selective permeability.

Selecting the Correct Option

Option (c) correctly defines selective permeability as it states that the cell membrane allows only certain materials to pass through.

Key concepts

Cell Membrane

The cell membrane, often referred to as the plasma membrane, is akin to a gatekeeper of a cell. Its role is to protect the cell's internal environment while allowing necessary substances in and out.

It's composed of a phospholipid bilayer with embedded proteins, which together create a fluid mosaic structure. This structure is dynamic and responsive to the cell's needs. Some substances can pass freely through the membrane, like oxygen and carbon dioxide, due to their size or the nature of the bilayer. However, other materials require specific proteins to facilitate their movement; for example, ion channels allow ions to pass through, and carrier proteins assist in the transport of larger molecules.

To understand the selective permeability of the cell membrane, it's essential to envision it as a barrier with several gates, each gate designed for a specific type of visitor.

Active Transport

When we think about active transport, consider it as the cell's energy-expending shipment process. This process is essential for maintaining specific conditions inside the cell, such as a high concentration of potassium ions.

It moves substances against their concentration gradient, from an area of lower concentration to an area of higher concentration, using energy typically derived from ATP. This means that the cell exerts energy to bring in or expel substances regardless of the natural flow direction. For instance, sodium-potassium pumps are a classic example of active transport mechanisms.

Passive Transport

Compared to the energy-intense active transport, passive transport is the cell's freewheeling mode of transportation. It does not require energy as it relies on the natural kinetic energy of particles. There are several ways this can happen:

• Diffusion: where substances move from an area of higher concentration to an area of lower concentration until equilibrium is achieved.
• Osmosis: a specific type of diffusion exclusive to water molecules.
• Facilitated diffusion: utilizes carrier proteins to move substances down their concentration gradient without using cellular energy.

Understanding these transport mechanisms clarifies why the cell membrane selectively allows substances through — it's leveraging the most efficient means to maintain balance across its border.