Question

Which of the following statements best explains how water enters root cells from the soil? a. Roots accumulate sugars from shoots, thereby increasing root cell ability to absorb water by osmosis. b. Roots actively pump water from the soil using the chemical energy of ATP. c. Water enters the spongy spaces between cells and within cell walls. d. Membrane-level transport of ions from soil into root hair cells increases the osmotic flow of water into them. e. Both c and d are correct.

Short answer

The correct statement is (e). Both c and d are correct. Water enters the spongy spaces between cells and within cell walls, and membrane-level transport of ions from soil into root hair cells increases the osmotic flow of water into them.

Step-by-step solution

Consider each statement individually

Understand the theory behind each statement. Statement (a) deals with sugars in shoots affecting osmosis, (b) refers to active transportation of water, (c) alludes to water entering via spaces between cells and cell walls, (d) describes the role of ion transport at the membrane level, and (e) suggests a combination of options (c) and (d).

Discard incorrect theories

Statement (a) is incorrect because sugar is sent from leaves to roots, resolving in a higher sugar concentration in roots, which leads to osmosis. However, the statement implies that roots send sugars to shoots. Statement (b) is incorrect because roots do not 'actively' pump water, they absorb it passively via osmosis. Although ATP is involved in absorbing minerals, it does not directly 'pump' water.

Analyze the remaining statements

Statement (c) indicating that water enters the spongy spaces between cells and within cell walls is partially correct, as water does move to areas of lower water potential with help from these spaces within the plant. Statement (d) implying that membrane-level transport of ions into root hair cells increases the osmotic flow of water is also correct, as the concentration of ions in the root cells does indeed increase the water potential causing water to flow into them. Hence, statement (e) suggesting that both (c) and (d) are correct, corroborates.

Finalize the correct statement

With this information, we can conclude that both statements (c) and (d) are correct because they both explain ways in which water can enter into root cells. Therefore, the correct answer would be (e), indicating that both of these processes occur.

Key concepts

Osmosis in Plant Roots

Osmosis is a fundamental concept for understanding how water is absorbed by plant roots. Essentially, osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process aims to equalize the solute concentrations on the two sides of the membrane.

Within the context of plant roots, osmosis occurs when the soil's water, which typically has a lower concentration of dissolved minerals (solutes), moves into the root cells, which have a higher solute concentration. The roots provide the perfect environment for osmosis with their semipermeable membranes that allow water to pass through while blocking larger solute molecules.

In reference to the exercise problem, water's entry into the plant root cells is driven by the difference in solute concentration between the inside of the root cells and the soil water. This osmotic flow is essential to the plant's ability to absorb water and is intricately tied to the ions' concentration within the root cells.

Active Transport in Plants

Active transport is the method by which plants intake certain substances against their concentration gradient, which requires energy in the form of ATP. Unlike osmosis, which is a passive process, active transport is an energy-dependent process.

In plants, active transport is utilized to absorb ions from the soil into root cells. These ions include potassium, nitrate, and phosphate, which are essential for plant growth and development. The presence of these ions inside the root cells lowers the water potential inside the cells, subsequently increasing the osmotic flow of water into them through a process known as osmotic pressure.

Even though the exercise's solution clarified that plants do not use active transport to 'pump' water directly, active transport indirectly influences water absorption. By actively transporting ions into the root cells, plants create a solute concentration gradient that facilitates water entry via osmosis.

Membrane-Level Ion Transport

Membrane-level ion transport refers to the movement of ions across the plant cell's plasma membrane. This process is crucial for maintaining cellular function and facilitating osmosis in plant roots.

Plant root cells contain specific proteins known as ion channels and pumps embedded within their membranes. These proteins allow the selective movement of ions, such as potassium and calcium, into and out of the cell. Ion pumps, powered by ATP, move ions against their concentration gradient, while ion channels allow ions to passively flow following their electrochemical gradient.

In line with the exercise's solution, the transport of ions into the root hair cells contributes to the buildup of a higher solute concentration within these cells. This leads to a decrease in water potential, which ultimately drives the osmotic flow of water into the plant cells. The coordination of membrane-level ion transport and osmotic water movement is a key mechanism by which water is absorbed efficiently from the soil into plant roots.