Membranes and Transport Flashcards
Define tonicity
a measure of the effective osmotic pressure gradient; the water potential of 2 solutions separated by a semi-permeable membrane
define hypotonic
solution has a higher water potential than the cell
define hypertonic
the solution has lower water potential than the cell
what are measurable and immeasurable ways of water loss
”- sensibile (measurable) - urine, poo, sweat
- insensible (immeasurable)- respiratory secretio,, diffusion through skin”
what are 3 abnormal ways of fluid loss
”- Urinary (polyuria): Common
- Gastrointestinal (vomiting, diarrhoea): Common
- Respiratory (fever, panting)
- Skin (burns, large wounds)
- Excessive salivation”
name 3 types of dehydration
isotonic fluid loss, hypertonic fluid loss, hypotonic fluid loss
describe isotonic fluid loss
”- Water and solute losses are equal eg sweating / haemorraging
- Fluid lost is isotonic so the same concentration as cells
- Extracellular volume decreases. But intracellular no change
- Fluid leaves plasma/extracellular fluid
- The concentration of electrolytes and water is the same as that which remains
- As there is the same water potential in extracellular fluid
- Therefore no driving force to remove fluid from the intracellular fluid”
describe hypertonic fluid loss
”- fluid is lost from the ECF and has high proportion of electrolytes relative to water
- Excessive perspiration, vomiting and diarrhoea, not drinking enough
- The ECF becomes hypotonic relative to ICF
- If more Na+ lost than water (relative)
- The extracellular fluid has a high water potential than intracellular
- Water moves into the intracellular out of the extracellular fluid
- Severe cases the cells will swell and cerebralswellingmay occur.
- manifests asneurological symptomsranging from headaches, nausea, lethargy, and potentially confusion, coma, and death”
describe hypotonic fluid loss
”- Water is lost from the ECF.
- The ECF then becomes hypertonic relative to ICF. - lower water potential
- Results in HYPERTONIC DEHYDRATION
- Inadequate water intake, excessive perspiration, osmotic diuresis (diabetes)
- E.G elevated serum sodium concentrationHypernatremia
- Too much water is lost from the extracellular fluid
- Water potential decreases in ECF relative to ICF
- Fluid moves from ICF to ECF resulting in intracellular dehydration
- leads to respiratory arrest and death”
describe crystalloid and colloid solutions
“Crystalloid solutions:
This is water and electrolytes that can pass between the membranes of cells easily. There are 3 types
Isotonic
Hypotonic
Hypertonic
Colloid solutions:
Contain insoluble molecules that can’t pass between membranes. Eg polysaccharides and proteins”
define simple diffusion
The net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration until equilibrium is reached. It is a passive process
describe exocytosis
process in which water-soluble and/or large substances are transported out of the cell within vesicles, without coming into direct contact with the lipid bilayer- requires energy
describe endocytosis
process in which water-soluble and/or large substances are transported into the cell within vesicles, without coming into direct contact with the lipid bilayer’- requires energy
what are the processes involving endocytosis
pinocytosis, phagocytosis
describe the steps of exocytosis of newly synthesised cells
“1.Proteins produced in rough ER are transported to the Golgi in vesicles
2.Proteins are sorted, modified and packaged into vesicles in the Golgi
3.The vesicles are transported to the cell membrane
4.Fusion of the vesicle lipid layers with the cell membrane occurs – this process is dependent on specific proteins in both membranes
5.Vesicle contents diffuse into the extracellular fluid”
what is endocytosis + examples
“process in which water-soluble and/or large substances are transported into the cell within vesicles, without coming into direct contact with the lipid bilayer’- requires energy
e.g. pinocytosis, phagocytosis”
steps to Pinocytosis (cell drinking)
“1. Cells take up fluid, dissolved substances, and particles from the extracellular fluid
2. A small membrane invagination forms
3. The invagination develops until it is ‘pinched off’ to form a vesicle
4. It usually results in the formation of many small vesicles
5. The vesicles may then:
fuse with lysosomes and the contents digested by phagocytosis
-break down releasing the vesicle contents into the cytoplasm.”
Phagocytosis steps
“1. Phagocytes have receptor molecules on their surface which bind to unique bacterial chemicals
2. pathogen engulfed by phagocyte
3. enters cytoplams in vesicle
4. fuses with lysosomes which release hydrolytic enzymes”
describe the cotransport of glucose
- sodium ions are actively transported out of the epithelial cell and into interstitial fluid via Na/K pump
- Creates a con gradient of Na between lumen and epithelial cell
- Sodium and glucose enter cell by facilitated diffusion- cotransport molecule
- sodium diffuses down conc gradient,
- glucose actively transports against conc gradient, energy from ATP
- glucose moves into IS, then blood via facilitated diffusion
describe phospholipids
The phosphate group head is polar and hydrophilic (‘water-loving’), while the 2 fatty acid chains of the tail are non-polar and hydrophobic (‘water-hating’).
what structures do phospholipids form in water
micelle or bilayer
why do phospholipids forma bilayer in plasma membranes (4 marks)
- Phospholipids have a polar phosphate group which are hydrophilic and will face the aqueous solutions
- The fatty acid tails are non-polar and will move away from an aqueous environment
- As both tissue fluid and cytoplasm is aqueous
- phospholipids form two layers with the hydrophobic tails facing inward
- and phosphate groups outwards interacting with the aqueous environment
Explain why the model for membrane structure is known as the fluid mosaic model (3).
- The phospholipid molecules can move freely laterally and makes the membrane fluid.
- The proteins are distributed throughout the membrane un evenly and in a mosaic pattern.
- The agreed structure is based upon experimental and chemical evidence and so is classed as a model.
what type of proteins does the plasma membrane (bilayer) contain
- glycoprotein
- signalling protein
- integral protein
- carrier protein
- receptor
- channel protein
Other than as carrier proteins state two functions of membrane bound proteins (2).
- Receptors
- Antigens
- Enzymes
- Structural (attached to microtubules
How can polar and non-polar molecules pass through the membrane (2).
Polar molecules require proteins to enable them to pass through the membrane
Non-polar molecules can diffuse directly through the phospholipid bilayer
whats the function of membranes
Selectively permeable barrier.
Structural, keeping the cell contents together.
Allows recognition of other external substances.
Allows mobility in some organisms, e.g. amoeba.
The site of various chemical reactions.
Allows communication with other cells.
describe partiall permeable membrane
small, fat-soluble, non polar molecules can simply diffuse,
others require a protein
define osmosis
diffusion of water. It is the net movement of water molecules from a region of high water concentration to a region of low water concentration, through a partially-permeable membrane
what is water potential
Water potential is the tendency of water molecules in a system to move. It is denoted by the symbol Ψ and is measured in kiloPascals (kPa).
Pure water has the highest water potential, and has a value of 0 kPa. Solutions have a lower water potential than pure water, and have a negative water potential.
define solute potential
reflects the number of dissolved molecules in a solution.
what is pressure epotential
reflects the amount of pressure on a solution. In a phenomenon called turgor pressure, the cell wall exerts pressure in plant cells, increasing the cell’s pressure potential.
what is ficks law
surface area x difference in conc / length of diffusion path
what affects the rate of diffusion
Increasing the distance (or thickness of the membrane) over which diffusion takes place will decrease the rate.
Increasing the surface area across which the particles diffuse, or increasing the size of the concentration gradient will increase the rate of diffusion.
