Biology Chapter on Osmotic Pressure

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Questions and Answers

Which of the following describes the effect of a hypotonic solution on a cell?

The cell will maintain its size with no change in volume.

The cell will shrink as water exits.

The cell will increase its size as water enters. (correct)

The cell will burst due to excessive water intake. (correct)

What is the primary reason for the swelling of cells placed in an isosmotic urea solution?

Urea cannot cross the cell membrane.

Water follows urea into the cell. (correct)

Osmolarity is equal on both sides of the membrane.

The concentration of electrolytes is higher inside the cell.

What condition occurs if red blood cells are placed in a hypertonic solution?

The cells will maintain their shape and volume.

The cells will experience shrinkage as water leaves. (correct)

The cells will fill with excess electrolyte ions.

The cells will swell and potentially burst.

What potential consequence might result from low plasma protein levels?

Fluid may accumulate in the interstitial spaces, leading to edema. Signup and view all the answers

What is a potential consequence of cerebral edema?

Possible hypoxia and damage to brain tissue. Signup and view all the answers

What is osmolarity defined as?

The concentration of all solutes in a solution expressed in Osm/L Signup and view all the answers

What is the primary driving force for osmosis?

Osmotic pressure differences across a membrane Signup and view all the answers

Which of the following statements about cell membranes is correct?

Cell membranes are selectively semipermeable to certain substances. Signup and view all the answers

If a solution in a cell has a higher concentration of sucrose compared to the surrounding solution, the solution in the cell is classified as:

Hyperosmotic Signup and view all the answers

In a solution with 1 mol/L NaCl, how many osmoles per liter does it produce?

2 Osm/L Signup and view all the answers

Which characteristic of aquaporins contributes to osmosis?

They increase the permeability of the membrane to water. Signup and view all the answers

What term best describes a solution with low solute concentration relative to another?

Hyposmotic Signup and view all the answers

What will happen to a cell placed in a hyperosmotic sucrose solution?

The cell will shrink. Signup and view all the answers

Which of the following best defines osmotic pressure?

The pressure exerted to prevent osmosis from occurring. Signup and view all the answers

How does a hypoosmotic solution affect a cell?

The cell swells. Signup and view all the answers

What is the approximate osmolarity of body fluid compartments?

300 mOsm Signup and view all the answers

What happens to water movement when two solutions are compared as isosmotic?

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

If the intracellular fluid (ICF) has an osmolarity of 300 mOsm/L, what would the osmolarity be in a solution that causes the cell to swell?

Below 300 mOsm/L Signup and view all the answers

Which term describes the condition when a cell neither swells nor shrinks in an external solution?

Isotonic Signup and view all the answers

What is the effect of an increase in solute concentration on osmotic pressure?

Osmotic pressure increases. Signup and view all the answers

Why does sucrose not cross the cell membrane during osmotic processes?

It is a large molecule. Signup and view all the answers

During osmotic equilibrium, which process maintains the balance of fluids between compartments?

Fluid shift 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 cellular and capillary levels

Osmolarity (Osmotic Concentration)

Osmolarity is the concentration of all solutes in a solution
Units of osmolarity are Osm/L (Osmoles per Litre)
Osmolarity is similar to molar concentration (M)
Units of osmolality are Osm/kg
Osmolarity values are usually similar to osmolality; however, osmolality accounts for solutes that contribute to the osmotic pressure of a solution
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

Cell membranes are selectively permeable
Allow hydrophobic (lipid-soluble) substances to pass easily
Allow some small hydrophilic (polar) substances to pass easily
Prevent the free passage of larger 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 via simple passive diffusion
Membrane permeability to water can be increased by aquaporins
Aquaporins are specialized water channels

Osmosis

Osmosis is a passive transport mechanism
Water moves from an area of high water concentration (high water potential) to an area of low water concentration (low water potential) across a semipermeable membrane
High solute concentration = low water concentration
Low solute concentration = high water concentration
Osmosis must occur through a semipermeable membrane that allows water but not other substances to pass
Osmosis is driven by osmotic pressure, the pressure required to prevent osmosis
The greater the solute concentration, the greater the osmotic pressure

Osmosis in Cells

A cell with a higher concentration of a solute will have a lower water concentration
Water will move from areas of higher water concentration to areas of lower water concentration
This will cause the cell to swell or shrink depending on the relative concentrations

Body Fluid Compartments

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

Comparing Osmolarity

Comparing osmolarity of solutions can be done using terms such as: isosmotic, hyposmotic, or hyperosmotic

Tonicity

Tonicity describes how a solution affects cell volume
Osmolarity is affected by all solutes present, while tonicity is only affected by solutes that cannot cross the membrane
A hypotonic solution will cause cells to swell
An isotonic solution will cause no change in cell volume
A hypertonic solution will cause cells to shrink

Comparing Tonicity

Consider the case of urea, which can cross the membrane, influencing the cell's water balance, despite similar osmolarity conditions

Osmotic Behaviour of Cells

RBCs placed in isotonic solutions (e.g., 0.9% NaCl) maintain normal shape and volume
RBCs placed in hypotonic solutions (e.g., water) swell and may burst (hemolysis)
RBCs placed in hypertonic solutions (e.g., 2% NaCl) shrink

How this Relates to Cells in the Body

Cell membranes are permeable to water, moving in and out by osmosis, influenced by solute concentration gradients across the ECF and ICF
Electrolytes contribute to body fluid osmolarity
ECF and ICF must have similar osmolarity to maintain balance
Osmosis occurs if water is lost from one compartment

Oedema (UK) / Edema (US)

Plasma proteins maintain osmotic pressure within blood vessels
Low plasma proteins can result in fluid leaving circulation and entering tissues, causing oedema
Causes include hypoproteinaemia conditions like liver or kidney disease, malabsorption, or nutritional lack

Cerebral Oedema

Cerebral oedema involves fluid accumulation in the brain, increasing intracranial pressure
Causes include stroke, tumors, head trauma
Severe consequences can include hypoxia, damage, and possibly death
Treatment includes hypertonic solutions like mannitol administered intravenously (IV)

Glossary of Terms

Includes definitions for isotonic, hypertonic, hypotonic, isoosmotic, hyperosmotic, hypoosmotic, relevant to osmolarity and tonicity

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Description

Dive into the concepts of osmotic pressure, osmolarity, and tonicity with this quiz. Learn to differentiate between hyposmotic, hyperosmotic, and isosmotic solutions, and understand the effects of osmosis on cells. This quiz will help reinforce your knowledge of these essential biological principles.