Question

Cells transport sodium ions out of the cell against the sodium concentration gradient. This is an example of: a. facilitated diffusion b. simple diffusion c. diffusion via channel proteins d. endocytosis e. active transport

Short answer

e. active transport

Step-by-step solution

Understanding the Question

Identify the process described in the question. The question states that sodium ions are transported out of the cell against the sodium concentration gradient.

Define Concentration Gradient

A concentration gradient refers to the difference in concentration of a substance between two regions. 'Against the concentration gradient' means moving from an area of lower concentration to an area of higher concentration.

Identify Possible Transport Mechanisms

List the options given and their definitions: a. Facilitated diffusion - movement of molecules across cell membranes through protein channels without energy. b. Simple diffusion - passive movement from high to low concentration without energy. c. Diffusion via channel proteins - movement through channel proteins without energy. d. Endocytosis - cellular process of engulfing materials. e. Active transport - movement of molecules against a concentration gradient with energy.

Match with the Correct Mechanism

Since the transport is against the gradient, it requires energy. Among the listed options, only 'Active transport' (e) involves energy for moving substances against their concentration gradient.

Key concepts

sodium ion transport

Sodium ion transport is a crucial process in many cellular functions. To maintain proper cell function, cells often need to move sodium ions (Na⁺) across their membranes.
This movement is typically from an area of higher sodium concentration to one of lower concentration, but sometimes it occurs in the opposite direction, which requires specific mechanisms. Transporting sodium ions out of the cell against the concentration gradient involves pushing sodium ions from inside the cell, where their concentration can be lower, to the outside, where their concentration is higher.
This can only be achieved through active transport mechanisms. The sodium-potassium pump is a well-known example.
It pumps three sodium ions out of the cell and two potassium ions into the cell per ATP molecule used, helping establish the necessary ionic balance and membrane potential in cells.

concentration gradient

The concentration gradient is a key concept in understanding cellular transport processes.
It refers to the difference in the concentration of a substance between two areas. Think of it like a slope: moving 'down' the concentration gradient means moving from an area of high concentration to an area of low concentration, similar to rolling downhill.
Conversely, moving 'up' (or 'against') the gradient means going from low concentration to high concentration, much like pushing up a hill.
In cells, many substances, including ions like sodium (Na⁺), naturally move down their concentration gradients by diffusion. However, to move substances against their concentration gradient, energy is needed, which leads us to the concept of active transport.

• An example is the sodium-potassium pump, which actively moves sodium ions out of the cell and potassium ions into the cell.

energy requirement in cell transport

Energy is crucial for active transport processes in cells. Unlike passive transport, which occurs naturally along the concentration gradient without energy input, active transport moves substances against the gradient and requires energy.
This energy usually comes in the form of adenosine triphosphate (ATP).
ATP releases energy when it is hydrolyzed into adenosine diphosphate (ADP) and an inorganic phosphate (Pi).

• For instance, the sodium-potassium pump (Na⁺/K⁺ ATPase) uses one molecule of ATP to move three sodium ions out of the cell and two potassium ions into the cell.
• This process is essential for maintaining cellular homeostasis, nerve impulse transmission, and muscle contraction.

Understanding the necessity of energy in these processes helps explain why cells must constantly produce ATP to sustain life functions and manage their internal environments effectively.