Question

Read the following statements and select the corred option. (i) Pure water has the highest water potential ie., zero. (ii) Process of diffusion does not require any input of energy. (iii) Water moves from the system containing water at higher water potential to the one having lower water potential. (a) Statements (i) and (ii) are correct. (b) Statements (ii) and (iii) are correct. (c) Statements (i) and (iii) are correct. (d) Statements (i), (ii) and (iii) are correct.

Short answer

All statements (i), (ii), and (iii) are correct, so the correct option is (d).

Step-by-step solution

Verify Statement (i)

Assess the accuracy of the first statement. By definition, pure water at standard conditions (temperature and pressure) is taken to have a water potential of zero. Since water potential is a measure of the potential energy in water and serves as an indicator of the direction water will flow, a higher water potential usually means there is a tendency for water to leave that system. Thus, pure water is considered to have the highest water potential, confirming statement (i) as correct.

Verify Statement (ii)

Examine the second statement pertaining to the process of diffusion. Diffusion is a passive transport process, meaning it does not require any additional energy to occur. Molecules move from an area of higher concentration to an area of lower concentration until equilibrium is reached, without the need for energy input. Therefore, statement (ii) is correct.

Verify Statement (iii)

Evaluate the accuracy of the third statement. It relates to the principle of water potential, stating that water moves from a region of higher water potential to a region of lower water potential. This is the fundamental concept behind osmosis, which is the movement of water across a semi-permeable membrane. Consequently, statement (iii) is also correct.

Conclusion

All three statements (i), (ii), and (iii) have been verified and found to be correct, based on the principles of water potential and diffusion. Hence, the correct option that includes all accurate statements is option (d).

Key concepts

Diffusion

Diffusion is a process that plays a vital role in the natural movement of molecules in biological systems. Imagine you open a bottle of perfume in a room; soon, the fragrance spreads throughout the space, from where it was concentrated to where there was none before. This is diffusion at work: the movement of molecules from an area of higher concentration to an area of lower concentration. It's a passive process, which means it doesn't require an external source of energy. Molecules move about due to their kinetic energy until there's an even distribution, or equilibrium, achieved.

In biological contexts, such as within our bodies, diffusion is a fundamental process allowing substances like oxygen and carbon dioxide to traverse cell membranes, providing cells with necessary materials and removing waste products.

Osmosis

Osmosis is a special type of diffusion, crucial for maintaining proper cell function. It refers specifically to the movement of water molecules across a semi-permeable membrane from an area with a higher water potential (or lower solute concentration) to an area with a lower water potential (or higher solute concentration). Think of water potential as a measure of water's ability to do work when it moves from one area to another, similar to pressure.

In simpler terms, osmosis helps regulate a cell's hydration level. It's why plant cells become turgid when water flows in, and why our cells can swell or shrink in different solutions. For organisms to thrive, osmosis needs to be carefully managed, often involving complex cellular mechanisms to maintain homeostasis.

Passive Transport

Passive transport encompasses methods by which molecules move across cell membranes without the use of the cell's energy. Along with diffusion and osmosis, which are both passive transport processes, there’s also facilitated diffusion. During facilitated diffusion, specific molecules are transported across cell membranes via proteins. These proteins act like selective tunnels, accommodating molecules that otherwise couldn't pass through the cell's lipid bilayer.

The beauty of passive transport lies in its energy efficiency. Cells maintain their essential functions and composition without expending precious energy - a concept that's critical in energy conservation within the body. In passive transport, the natural kinetic movement of molecules is harnessed to fulfill vital biological processes.

Concentration Gradient

The concentration gradient is a term used to describe the difference in the concentration of a substance between two regions. It's the driving force behind the direction and rate of diffusion and osmosis. Think of it as a hill: molecules naturally 'roll down' from an area of high concentration (top of the hill) to an area of low concentration (bottom of the hill).

In the context of cells, maintaining and utilizing concentration gradients is essential for nutrient uptake and waste removal. Cellular energy pumps often work against the gradient, moving substances from lower to higher concentration, which requires energy - a process known as active transport. However, when it comes to passive transport, the concentration gradient does all the work, guiding molecules in the necessary direction without any energy cost.