Water Potential and Osmoregulation in Plant and Animal Cells

What is osmoregulation?

The regulation of osmotic pressure or water content to maintain internal fluid balance.

How do animal cells maintain their volume?

By keeping their cytosol isotonic to the extracellular environment and using the Na+/K+ pump to export ions.

What happens if too many solutes enter an animal cell?

It can lead to an influx of water, increasing cytosolic solute concentration and potentially causing cell lysis.

What is the role of the Na+/K+ pump in animal cells?

It exports Na+ ions to prevent cell lysis and maintain osmotic balance.

How do plant cells control their volume?

They have a rigid cell wall that limits volume changes and can withstand pressure from water influx.

What is water potential?

The potential energy of water, quantifying its tendency to move from one area to another, measured in pressure units.

What are the two components of water potential in plant cells?

1) Solute potential (ψS), which decreases with solute addition; 2) Pressure potential (ψP), which is typically positive due to cell wall resistance.

What is turgor pressure?

The osmotic pressure within plant cells that pushes the plasma membrane against the cell wall, keeping plants upright.

What is the water potential of pure water?

Zero; any solution with a water potential less than zero tends to take up water from pure water.

What is the difference between osmoregulators and osmoconformers?

Osmoregulators actively manage water and solute levels, while osmoconformers match their internal osmotic pressure to their environment.

How do marine bony fishes manage water loss?

They drink seawater to offset water loss and actively transport chloride ions out to maintain hypoosmolarity.

What adaptations do freshwater animals have for osmoregulation?

They excrete large amounts of dilute urine and actively uptake salts from their surroundings.

What is the significance of impermeable surfaces in land animals?

They help reduce water loss while allowing for necessary gas exchange.

What are transport epithelia?

Layers of cells that transport substances across membranes, crucial for maintaining cellular composition.

How do marine birds excrete excess salt?

They have specialized nasal salt glands that actively pump ions from the blood and excrete them through the nasal cavity.

What is the consequence of a plant cell decreasing its cytoplasmic solute concentration?

Water is likely to move out of the cell by osmosis, increasing the total water potential of the cell.

What is osmotic pressure?

The pressure required to prevent the inward flow of water across a semipermeable membrane.

What is the relationship between solute concentration and water movement?

Water moves toward regions of higher solute concentration, following the concentration gradient.

What happens to plant cells in a hypotonic solution?

They experience an influx of water, leading to increased pressure without significant volume change due to the cell wall.

Why can't humans gain net water from drinking seawater?

Humans cannot excrete salt at high enough concentrations to offset the salt intake from seawater.

What is the effect of dehydration on cells?

Excessive dehydration can impair metabolic functions and damage cells.

What is the primary function of osmoregulation?

To maintain the composition of cellular cytoplasm and prevent harmful osmotic pressure changes.

What is the osmolarity of freshwater animals compared to marine animals?

Freshwater animals have lower solute concentrations in their body fluids than marine animals.

What is the role of vacuoles in plant cells?

They store solutes and help maintain turgor pressure by regulating water influx.

What is the consequence of water moving by osmosis?

Water moves across a semipermeable membrane toward areas of lower (more negative) water potential.

What are the two components of water potential in living plant systems that were not discussed in class?

Matric potential and gravitational potential.

What is matric potential?

The potential energy of water due to adhesive forces that bind water to physical objects such as soil particles or cell walls.

What is gravitational potential?

The potential energy of water resulting from the pressure of gravity on it.

What type of plant cell is found in an isotonic solution?

Flaccid.

What type of plant cell is found in a hypertonic solution?

Plasmolyzed.

What type of plant cell is found in a hypotonic solution?

Turgid.

What is the equation for water potential in isolated plant cells?

Ψw = Ψs + Ψp, where Ψw is water potential, Ψs is solute potential, and Ψp is pressure potential.

What is the solute potential (Ψs) and pressure potential (Ψp) for a plasmolyzed cell with a water potential of -1.0 MPa?

Ψs = -1.0 MPa, Ψp = 0.0 MPa.

What is the solute potential (Ψs) and pressure potential (Ψp) for a flaccid cell with a water potential of -0.5 MPa?

Ψs = -0.5 MPa, Ψp = 0.0 MPa.

What is the solute potential (Ψs) and pressure potential (Ψp) for a turgid cell with a water potential of 0.0 MPa?

Ψs = -0.1 MPa, Ψp = +0.1 MPa.

How does a decrease in the water potential of the surrounding solution affect water uptake by a plant cell?

It enhances water uptake by making the surrounding solution more negative, encouraging water to move into the cell.

What would happen if a plant cell with Ψs of -0.7 MPa is placed in a solution with Ψ of -0.4 MPa?

The cell's pressure potential (Ψp) would be +0.3 MPa at equilibrium.

Why is the loss of solutes from the cell incorrect in enhancing water uptake?

Because the loss of solutes would increase the water potential in the cell, making it less likely for water to move in.

What is the pressure potential (Ψp) of a plant cell with Ψs of -0.65 MPa in a solution with Ψs of -0.30 MPa?

Ψp would be +0.35 MPa.

What is the relationship between solute concentration and water potential in plant cells?

Two solutions can be at equilibrium when their water potentials are the same, regardless of solute concentrations.

What effect does positive pressure on the surrounding solution have on water uptake?

It enhances water uptake by pushing water into the plant cell.

What is the significance of the rigid cell wall in plant cells regarding water movement?

The pressure exerted by the rigid cell wall is a significant factor in determining the net movement of water.