Osmotic Pressure and Osmolarity Quiz

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Questions and Answers

What happens to a cell when it is placed in a hyperosmotic solution?

The cell undergoes lysis.

The cell remains the same size.

The cell shrinks due to water loss. (correct)

The cell swells due to water intake.

What is osmotic pressure?

The pressure exerted by water molecules in a container.

The pressure required to prevent osmosis. (correct)

The pressure that pushes water into a solution.

The pressure that increases with decreased solute concentration.

Which term describes a solution that has the same osmolarity as a cell?

Hypoosmotic

Isoosmotic (correct)

Tonic

Hyperosmotic

Which of the following is an example of a hyposmotic solution?

100 mmol/L sucrose. Signup and view all the answers

How does a change in the concentration of intracellular fluid (ICF) or extracellular fluid (ECF) affect the body?

It results in fluid shift between compartments. Signup and view all the answers

What occurs when a cell is placed in an isosmotic sucrose solution?

There is no net movement of water. Signup and view all the answers

What is the effect of a hypotonic solution on a cell?

The cell swells and may undergo lysis. Signup and view all the answers

What is typically the osmolarity of body fluid compartments?

300 mOsm Signup and view all the answers

What determines osmolarity in a solution?

The concentration of all solutes present Signup and view all the answers

Which of the following terms describes a solution with a lower solute concentration compared to another solution?

Hypotonic Signup and view all the answers

How does osmosis primarily occur across cell membranes?

Diffusion of water molecules Signup and view all the answers

What role do aquaporins play in cellular osmosis?

They serve as water channels to facilitate water movement Signup and view all the answers

If a cell containing 360 g/L sucrose is placed in a beaker with 180 g/L sucrose, what will happen to the cell?

Water will leave the cell, causing it to shrink Signup and view all the answers

Which of the following statements about tonicity is true?

Tonicity refers only to the osmolarity of solutes that cannot cross the membrane. Signup and view all the answers

What is the primary driving force behind the process of osmosis?

Osmotic pressure differences Signup and view all the answers

A solution of 1 mol/L NaCl is equivalent to how much osmolarity?

2 Osm/L Signup and view all the answers

What is tonicity primarily affected by?

Only solutes that cannot cross the membrane Signup and view all the answers

What occurs when a cell is placed in a hypotonic solution?

The cell swells and may burst Signup and view all the answers

Which solution would cause a red blood cell to undergo haemolysis?

Water Signup and view all the answers

What is likely to cause oedema in tissues?

Low plasma proteins Signup and view all the answers

How does the body maintain osmolarity between the extracellular fluid (ECF) and intracellular fluid (ICF)?

By ensuring the osmolarity is equal between the two compartments Signup and view all the answers

What is the impact of placing a red blood cell in a hypertonic solution?

The cell shrinks due to water exiting Signup and view all the answers

In the context of cerebral oedema, what condition is associated with increased intracranial pressure?

Stroke Signup and view all the answers

What treatment is commonly used for cerebral oedema?

Hypertonic mannitol solution Signup and view all the answers

Study Notes

Objectives

Define osmotic pressure
Calculate osmolarity and osmolality
Understand terms hyposmotic, hyperosmotic, isosmotic
Understand the difference between osmolarity and tonicity
Understand the effects of osmosis at the level of the cell membrane and the capillary wall

Osmolarity (Osmotic Concentration)

The concentration of all solutes in a solution
Units of osmolarity: Osm/L (Osmoles per Litre)
Osmolar (same as molar concentration, M)
Units of osmolality: Osm/kg
Usually similar values, variation takes into account only solutes contributing to osmotic pressure
Some substances dissociate in solution
- 1 mol/L glucose = 1 Osm/L
- 1 mol/L NaCl = 2 Osm/L
- 1 mol/L CaCl₂ = 3 Osm/L

Cell Membranes

Selectively semipermeable
- Allow hydrophobic (lipid-soluble) substances to cross easily
- Allow some small hydrophilic (polar) substances to cross easily
- Prevent the free passage of large polar substances (e.g., glucose, ions)

Movement of Water Across Cell Membranes

Water is a polar molecule (+/-)
Small amounts of water pass through the lipid bilayer by simple passive diffusion
Membrane permeability to water can be increased by the presence of aquaporins
- Specialized water channels

Osmosis

Passive transport mechanism
- Diffusion of water from an area of high water concentration (high water potential) to an area of low water concentration (low water potential) across a partially permeable membrane
- High solute concentration = low water concentration
- Low solute concentration = high water concentration
Diffusion of water
- Must be across a semipermeable membrane
  - Permeable to water
  - Impermeable to at least one solute
- Along a concentration gradient
- Driving force for osmosis is osmotic pressure (i.e., dilute to concentrated)

Osmosis Example

Solution in beaker contains 180 g/L sucrose
Solution in "cell" contains 360 g/L sucrose
"Cell" membrane permeable to water but not sucrose
Water moves into the cell, causing the cell to swell.
Water continues to move until concentration equalizes on both sides (~270 g/L sucrose)

Osmosis and Osmotic Pressure

Osmotic pressure = pressure required to prevent osmosis
Pressure exerted on the box = osmotic pressure
The greater the solute concentration, the greater the osmotic pressure

Body Fluid Compartments

In the body, all compartments are normally in osmotic equilibrium (~300 mOsm)
Changes in concentration of ICF or ECF result in fluid shifts between compartments

Comparing Osmolarity

Comparing osmolarity of 2 solutions using the terms isosmotic, hyposmotic, or hyperosmotic
- A cell placed in an isosmotic sucrose solution: no net water movement, no change in cell volume
- A cell placed in a hypoosmotic sucrose solution: water moves into the cell, causing cell swelling (oedema)
- A cell placed in a hyperosmotic sucrose solution: water moves out of the cell, causing cell shrinkage

Tonicity

Describes the behavior of cells in solutions
- Do cells swell, shrink, or stay the same size?
Osmolarity is affected by all solutes, while tonicity is only affected by solutes that cannot cross the membrane
- Hypotonic solution: causes cells to swell (less solutes outside cell, water enters the cell)
- Isotonic solution: causes no change in cell volume (equal solutes on both sides of the membrane)
- Hypertonic solution: causes cells to shrink (more solutes outside cell, water exits the cell)

Comparing Tonicity Example

"Cell" in 300 mmol/L urea solution (isosmotic). Urea enters cell followed by water. Cell swells (oedema).

Osmotic Behavior of Cells

RBCs placed in isotonic solution: maintained shape and volume
RBCs placed in hypotonic solution: swell, may burst (haemolysis)
RBCs placed in hypertonic solution: shrink

How Does This Relate to Cells in the Body?

Cell membranes are permeable to water, water passes in and out by osmosis
Movement depends on solute concentration in ECF and ICF
Electrolytes contribute to osmolarity of body fluids
ECF and ICF must have the same osmolarity
Osmosis occurs if water is lost from one fluid compartment
Body fluid osmolarity is approximately 270-300 mOsm/L

Oedema

Plasma proteins provide osmotic pressure to keep fluid in blood vessels
If plasma proteins are low, fluid leaves the plasma and moves into tissues
Hypoproteinaemia (low plasma proteins) is caused by liver disease, kidney disease, malabsorption, or malnutrition
Oedema (swelling) due to fluid moving from intravascular space to interstitial fluid

Cerebral Oedema

Stroke, tumours, trauma cause fluid accumulation in the brain
Increased intracranial pressure, hypoxia, and damage can lead to death
Treatment often involves hypertonic solutions (e.g., mannitol) intravenously to decrease swelling

Terms Referring to Osmolarity and Tonicity of Solutions

Isotonic: solution does not change cell volume (containing 300 mOsm/L of non-penetrating solutes, regardless of the concentration of membrane-penetrating solutes)
Hypertonic: causes cells to shrink (containing greater than 300 mOsm/L of non-penetrating solutes)
Hypotonic: causes cells to swell (containing less than 300 mOsm/L of non-penetrating solutes)
Isoosmotic: containing 300 mOsm/L solute, (regardless of its composition of membrane-penetrating and nonpenetrating solutes)
Hyperosmotic: containing greater than 300 mOsm/L of solutes
Hypoosmotic: containing less than 300 mOsm/L of solutes

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Description

Test your understanding of osmotic pressure, osmolarity, and osmolality with this quiz. You will explore key concepts such as hyposmotic, hyperosmotic, and isosmotic solutions, as well as the effects of osmosis on cell membranes and capillary walls.