Question

If cell \(A\) with DPD 5 atm is surrounded by many cells with DPD 4 atm then (a) the net movement of water will be from cell \(A\) to the surrounding cells (b) net movement of water will be from the surrounding cells to cell \(A\) (c) water will not move at all (d) water movement will depend on other unknown factors.

Short answer

The net movement of water will be from the surrounding cells to cell A (DPD 4 atm to DPD 5 atm).

Step-by-step solution

Understand the Concept of Diffusion Pressure Deficit (DPD)

Diffusion Pressure Deficit (DPD) is a measure of the potential of water to move from one area to another due to osmosis. A higher DPD value indicates a higher potential for water to move out of the cell, while a lower DPD value suggests a lower potential for water to move into the cell.

Compare DPD Values

Identify the DPD of the central cell, which is 5 atm, and compare it with the DPD of the surrounding cells, which are 4 atm. Since the surrounding cells have a lower DPD, they are at a higher water potential compared to cell A.

Determine the Direction of Water Movement

Water movement due to osmosis occurs from a region of lower DPD to a region of higher DPD. Therefore, water will move from the surrounding cells into cell A, which has a higher DPD.

Key concepts

Osmosis

Osmosis is a fundamental biological process involving the movement of water across a selectively permeable membrane. It occurs spontaneously when there is a difference in the concentration of solutes, and hence water potential, on either side of the membrane.

Consider a plant cell: the selectively permeable membrane is the cell membrane, surrounded by the cell wall, which offers structural support. In osmosis, water moves from an area of higher water potential (or lower solute concentration) to an area of lower water potential (or higher solute concentration) until equilibrium is reached.

In the context of the given problem, cell A, which has a Diffusion Pressure Deficit (DPD) of 5 atm, is surrounded by cells with a lower DPD of 4 atm. This indicates that cell A has a higher solute concentration and lower water potential, prompting water to move into it via osmosis from the surrounding cells, which have a higher water potential.

Water Potential

Water potential, represented by the symbol \( \Psi \), is a measure that combines the effects of solute concentration and pressure to determine the direction of water flow. It's crucial in understanding how water moves through plants, soils, and cellular environments. The unit of measurement for water potential is typically megapascal (MPa).

Water will always move from an area of higher water potential to an area of lower water potential. Pure water at standard conditions (atmospheric pressure) is defined to have a water potential of zero, and the presence of solutes or applied pressure can modify this potential.

Cell A's higher DPD indicates a lower water potential than its neighboring cells. Due to this potential difference, osmosis will drive water into cell A, seeking to balance the water potential between cell A and the surrounding cells.

Cellular Transport

Cellular transport refers to the movement of substances across cell membranes. In cells, this can happen passively or actively, depending on the energy requirements and direction relative to concentration gradients.

Passive transport, which includes osmosis, does not require energy as substances move along their concentration gradient. On the contrary, active transport requires energy, often from ATP, to move substances against their concentration gradient.

The scenario presents a passive transport case where water moves according to the concentration gradient through osmosis. Cell A, with a higher DPD, will see water entering because, in terms of water potential, water passively gravitates toward the region of lower potential, in this case, the interior of cell A.