Question

Movement of the molecules of solids, gases or liquids from the region of their higher concentration to the region of their lower concentration is known as (a) diffusion (b) osmosis (c) imbibition (d) active transport.

Short answer

The movement of molecules from a region of higher concentration to that of lower concentration is known as (a) diffusion.

Step-by-step solution

Understanding the Concept

Consider the process described in the question which is the movement of molecules from an area of higher concentration to an area of lower concentration.

Identifying the Correct Process

Match the described process with the correct term from the provided options. This movement of molecules is known as diffusion, which is a passive transport mechanism that occurs in solids, liquids, and gases.

Eliminating Incorrect Options

Osmosis is the diffusion of water through a semi-permeable membrane, imbibition is the absorption of water by solid particles of a colloidal size which causes an increase in volume, and active transport requires energy to move molecules against the concentration gradient. Therefore, these options do not describe the given process.

Key concepts

Passive Transport Mechanisms

Passive transport is a vital biological process that enables substances to move across cell membranes without the cell expending energy. It's driven purely by the natural tendency of molecules to spread out and occupy available space more evenly. Imagine a crowd gradually dispersing after a concert - no one tells them to move, but they slowly spread out to exit the venue more comfortably.

There are several types of passive transport, diffusion being the fundamental and most straightforward type. Others include osmosis, as mentioned in your textbook, and facilitated diffusion, where membrane proteins help substances that cannot directly diffuse through the lipid bilayer, glide across smoothly. Another key point to consider is that passive transport allows cells to maintain homeostasis, or stable internal conditions, by regulating the influx and efflux of molecules in response to the cell's needs without using energy (ATP).

Molecular Movement

Molecular movement is at the heart of diffusion and is governed by the kinetic energy of molecules. Each molecule moves randomly and independently of others; their motion causes them to collide and scatter in new directions. You can visualize it as a dance where every molecule moves to its own rhythm without a set routine.

Temperature plays a key role here - the higher the temperature, the faster the molecules move, leading to increased rates of diffusion. Similarly, smaller molecules move quicker than larger ones, so oxygen will diffuse more rapidly than glucose. It's important to note that this movement doesn't need an input of extra energy; it's a natural occurrence whenever there are molecules in a space. This inherent 'restlessness' of particles is what ultimately leads to substances spreading throughout an available space until they are uniformly distributed.

Concentration Gradient

The concentration gradient is a simple yet powerful concept that dictates the direction and rate of diffusion. It's essentially the slope that represents the change in concentration of a substance across a space. But you can think of it as a hill: molecules will naturally 'roll down' from where they're crowded (the top of the hill) to where they have more space (the bottom).

The steeper this 'hill,' or gradient, the faster the rate of diffusion, much like how a steep hill makes for a quicker descent. This is because there's a greater force driving the movement of molecules towards areas of lower concentration. The gradient evens out over time as molecules redistribute themselves evenly, reaching a state of equilibrium where there's no longer a net movement in any particular direction. Through diffusion, substances essential for cell survival, like oxygen and nutrients, are distributed throughout the organism by riding down their own concentration gradients.