Osmosis and diffusion

Question 1

Extracellular fluid

Answer 1

fluid outside of the cell

Question 2

Intracellular fluid

Answer 2

fluid inside of the cell

aka cytoplasm

Question 3

Cytoplasm

Answer 3

Means ‘cell substance’.

Gel-like, fluid-matrix of cytosol containing organelles and molecules.

Question 4

Eukaryotic animal cell - The plasma membrane

Answer 4

referred to simply as the cell membrane or cytoplasmic membrane.

• boundary of the cell, protecting the organelles; it holds the cell together.
• Regulates movement of material into and out of the cell.
• Important role in cell communication

It is a phospholipid bilayer.

• made up of lipids and proteins.
• Consists of a hydrophilic (water-loving) outer and hydrophobic (water-hating) core.
• Composition of the membrane can change as required.

Aspects of the structure can be removed as well as new/additional material added

Question 5

Main composition of membrane

Answer 5

Lipids
– Phospholipids, glycolipids, sterols, amphipathic lipids.
• Amphipathic – has both hydrophilic and lipophilic (fat-loving) regions.

Proteins
– Integral (transmembrane) proteins, peripheral proteins, lipidanchored proteins.

Carbohydrates
– Glycoproteins, some glycolipids.

Question 6

Transport processes - Simple diffusion

Answer 6

Movement of a substance from an area of high concentration to an area of low concentration,

e.g. Carbon dioxide leaving cells

Question 7

Transport processes - Osmosis

Answer 7

Special form of diffusion which only applies to water. It is the movement of water from a region of high water potential to a region of low water potential across a semi-permeable membrane.

e.g. Movement of water into and out of cells

Question 8

Transport processes - Channel-mediated passive transport (facilitated diffusion)

Answer 8

Diffusion of particles across a membrane via membrane-bound channel proteins (movement down a concentration gradient)

e.g. Movement of sodium ions into nerve cells

Question 9

Transport processes - Carrier-mediated passive transport (facilitated diffusion)

Answer 9

Diffusion of particles across a membrane via membrane-bound carrier proteins (movement down a concentration gradient)

e.g. Movement of glucose into cells

Question 10

Diffusion

Answer 10

The movement of a substance from an area of high concentration to an area of low concentration

• Particles diffuse as they make contact with other particles and are moved in different directions.
• Diffusion occurs down a concentration gradient

Question 11

Simple diffusion

Answer 11

Where molecules pass through the plasma membrane directly

• Examples of molecules able to pass: O2, H2O, CO2, N2
• They move by dissolving into the fluid of the phospholipid layer and then diffusing across it.
• When molecules cross the membrane they have permeated the membrane.

Question 12

What is Dialysis?

Answer 12

Artificial filtration/cleaning of the blood to remove waste products, toxins etc.

– Dialysis is a means of keeping someone suffering late - stage chronic kidney disease alive while a suitable kidney donor is located

– One of two methods:
• Pump passing blood via special membrane in place of kidneys to remove waste products

• Allowing waste products to diffuse directly into special dialysis fluid within the body

Question 13

How does Dialysis work?

Answer 13

– Relies on diffusion.

– Two types haemodialysis and peritoneal dialysis

Question 14

Haemodialysis

Answer 14

– Blood from radial artery passed through membrane which allows small waste particles such as urea to diffuse out into a special dialysis fluid; large particles (e.g. blood cells) are retained

– The filtered blood is then returned to the patient via a suitable vein in the leg or wrist

Question 15

Peritoneal dialysis

Answer 15

– Sterilised dialysis fluid is introduced into the peritoneal cavity of the patient through the abdominal wall

– The membrane of the cavity allows waste products from the blood to pass through and into the dialysis fluid.

– After 2-3 hours the dialysis fluid is drained from the patient and replaced with fresh for another cycle.

Question 16

Osmosis

Answer 16

The movement of water from a region of high water potential to a region of low water potential across a semi-permeable membrane

• Osmosis: special form of diffusion which only applies towater.

• Higher water potential = lower solute concentration.
• Lower water potential = higher solute concentration.

• Water potential has the symbol Ψ (psy).

Question 17

Osmotic pressure

Answer 17

Movement of water either into or out of a cell will cause changes in the pressure both inside and outside of that cell.

Pressure within a solution which has been caused by osmosis is called osmotic pressure.

• Potential osmotic pressure
– The maximum pressure which could develop in a solution.

• Actual osmotic pressure
– The pressure which exists in the solution at that moment.

Question 18

Homeostasis

Answer 18

“Maintenance of relatively constant states within the body”

• Homeostasis is essential for correct physiology: osmotic pressure, volume, ion concentrations, blood sugar, pH etc.
• Homeostasis of volume and pressure is particularly essential to healthy cellular function.
• Both tend to be maintained at a constant rate as intracellular fluid is maintained at the same potential osmotic pressure as the extracellular fluid

Question 19

Isotonic

Answer 19

Where two regions of fluid have the same potential osmotic pressure as each other.

• Iso: meaning ‘same’.
• Tonic: meaning ‘pressure’.

• Isotonic solutions have the same potential osmotic pressure (and water potential) because they each contain the same concentration/s of solute/s.

Question 20

Hypertonic

Answer 20

Higher pressure. Greater solute content (low water potential).

Question 21

Hypotonic

Answer 21

Lower pressure. Lower solute content (high water potential).

Question 22

Disorders of water balance

Answer 22

Extreme, prolonged shifts in water balance within the body and its cells has important consequences for physiology.

• Too much water is as bad for physiology as too little!
• Net effects on cells are similar.

Dehydration and water intoxication

Question 23

Dehydration

Answer 23

Where you use/lose more fluid than you take in

Stages of dehydration can broadly be defined by the % loss of body weight as follows:

• 5% – Mild
• 10% – Moderate
• 15% – Severe

Changes the osmotic balance of the body.

• Balance of minerals in your body also changes.
• Turgidity of cells decreases as water leaves cells.
• Severe dehydration can result in rupture and death of cells (cell lysis).

Question 24

Dehydration Symptoms

Answer 24

Dry and irritated skin, loose skin, bags under the eyes, headaches, general weakness, dizziness, confusion, dry mouth, difficulty swallowing, dry and tired feeling eyes

Question 25

Water intoxication

Answer 25

Where you take in more water than you use, resulting in dilution of salts and other minerals

Results in hyponatremia – situation where sodium content of your blood is below normal.

• Changes the osmotic balance of the body.
• Balance of minerals in your body also changes, you risk dangerously diluting out your electrolytes.
• Turgidity of body cells increases as water enters cells.
• Severe water intoxication can result in death as cells of the body swell, rupture and die (cell lysis).

Question 26

Water intoxication symptoms

Answer 26

Nausea, headaches, pressure in your head, altered vision (things moving or inability to see properly), feeling cold and confused; eventually leading to coma

Question 27

Facilitated diffusion

Answer 27

The assisted transport of certain molecules across the plasma membrane using either protein channels or carriers

Question 28

Channel-mediated passive transport

Answer 28

Cell membrane has specialised proteins called membrane-bound channel proteins.

• Channels allow specific ions or small, water-soluble molecules to cross the membrane.
– Channels allow these molecules to avoid the hydrophobic core of the plasma membrane.

Question 29

gated channels

Answer 29

Able to open and close to the passing of molecules

Important role in pathology and homeostasis.

Question 30

Several methods control channel access:

Answer 30

– Chemical signals.
– Mechanical signals.
– Electrical signals.
– Light signals.

Question 31

aquaporins

Answer 31

• Specialised water-channels

* These allow water to move across quicker than by simple diffusion

Question 32

Carrier-mediated passive transport

Answer 32

Cell membrane has specialised proteins called membrane-bound carrier proteins.

they actively change shape

• carrier proteins will typically only permit specific molecules to bind.
• They allow hydrophilic molecules to avoid the hydrophobic core of the plasma membrane.

Question 33

Carrier proteins transport permitted molecules by

Answer 33

1. Molecule within vicinity of the carrier protein is deemed permissible.
2. Carrier protein undergoes conformational change to fit the shape of the molecule to be transported, allowing it to enter the carrier.
3. Further change allows the molecule to be ejected from the carrier and either into or out of the cell.