Question

What is the biological importance of \(\mathrm{Na}\) and \(\mathrm{K}\) ions in cell fluids like blood plasma? (a) They participate in transmission of nerve signals. (b) They regulate the number of red and white blood corpuscles in the cell. (c) They can be present in any amount in the blood since they are absorbed by the cells. (d) They regulate the viscosity and colour of the blood.

Short answer

(a) Na and K ions are crucial for the transmission of nerve signals due to their role in generating and maintaining the membrane potential necessary for the conduction of electrical impulses.

Step-by-step solution

Identifying the Role of Sodium (Na) and Potassium (K)

Sodium (Na) and Potassium (K) ions play a crucial role in several physiological processes within the body. Their concentration gradients across cell membranes are vital in maintaining cell potential and are actively involved in the conduction of electrical signals in neurons.

Assessing the Options Provided

Assess each provided option in the context of the known biological functions of Na and K ions:(a) Transmission of nerve signals is a well-documented role of Na and K due to the Na+/K+ pump.(b) While ions can influence cell functions, there's no direct regulation of red and white blood cell counts by Na and K ions alone.(c) The concentrations of Na and K are tightly regulated within the blood plasma, not absorbed in any amount.(d) They do not directly regulate the viscosity and color of blood; these are functions of other components like red blood cells and plasma proteins.

Determining the Correct Option

Based on known physiological roles of Na and K ions, the correct option is (a) They participate in the transmission of nerve signals.

Key concepts

Transmission of Nerve Signals

One of the key roles of sodium (Na) and potassium (K) ions in the human body is in the transmission of nerve signals. Neurons, the specialized cells of the nervous system, communicate through electrical impulses. These impulses are generated by a sudden change in the electric potential across cell membranes.

To understand this process, imagine a neuron at rest where there is a higher concentration of Na ions outside the cell and a higher concentration of K ions inside the cell. This creates a voltage difference, known as the resting membrane potential. When a nerve signal is initiated, there is a rapid influx of Na ions into the neuron, causing depolarization. Subsequently, K ions exit the cell, repolarizing the membrane to its resting state.

These orchestrated movements of Na and K ions are critical, and are driven by the Na+/K+ pump, an active transporter that uses energy to maintain the gradient needed for nerve impulse conduction. The process is a beautiful dance of ions that work in tandem to quickly relay messages from our brains to the rest of our bodies, allowing us to react to stimuli.

Regulation of Cell Potential

The regulation of cell potential is essential for maintaining normal cellular function, and this is where Na and K ions play another vital role. Cell potential, which includes both the resting membrane potential and the action potentials, is the electric charge difference across the cell membrane.

The resting membrane potential is set up by the difference in concentration of Na and K ions inside and outside of cells. It is maintained by the selective permeability of the cell membrane and active transport mechanisms such as the Na+/K+ pump. This enzyme-driven pump exchanges three Na ions out of the cell for two K ions into the cell, consuming ATP in the process.

When action potentials, or signals, are generated, the cell potential changes dramatically, leading to a cascade of events that result in cellular responses. This includes muscle contractions and the firing of neurons. The precision in the control of cell potential by Na and K ions is what allows our hearts to beat and our muscles to move with remarkable coordination.

Concentration Gradients in Cell Membranes

Concentration gradients in cell membranes are fundamental for a variety of biological processes, including but not limited to, the generation of nerve impulses. This gradient refers to the difference in concentration of a substance, like Na or K ions, across a membrane.

Cell membranes are selectively permeable, meaning they allow some substances to pass more easily than others. Na and K ions, for instance, cannot freely diffuse across the membrane; their movement is facilitated by proteins that span the membrane, including ion channels and ion pumps like the Na+/K+ pump.

The energy-dependent maintenance of these gradients is not for naught. They are the driving force behind the electrical signals that mediate neuron communication and the absorption and secretion of nutrients and waste products. Furthermore, they influence osmotic balance, which affects cell volume and pressure. Consequently, these ion gradients are not just maintaining electric potential but are also integral to the survival and proper function of cells.