UCL MBBS Year 1 FHMP UPDATED ACTUAL QUESTIONS AND
CORRECT Answers
What limits cell size? Surface area to volume ratio!
Larger cells are less efficient in moving nutrients and waste across the
cell membrane.
As cell size increases, distance for to As cell size increases, distance for TOXINS, IONS, etc. to diffuse from the
diffuse from the nucleus increases. nucleus increases.
What can nano-devices be used for and why? They can interact with the receptors on the surface of cells and inside
cells because they are 100-10,000 times smaller than human cells.
How much of the body's lean mass is water? Around 2/3
What are hydrophilic substances? Ones that are polar (e.g. Na+, glucose, many proteins) and so are able to
dissolve in water
What are hydrophobic substances? Ones that are non-polar (e.g. fats and waxes) so cannot dissolve in water
What are amphiphilic substances? Ones that contain polar and non-polar regions (e.g. phospholipids - have
hydrophilic phosphate head and hydrophobic fatty acid tails)
What is intracellular water? Water found inside the cells: makes up 2/3 of the body's water.
Where is extracellular water found? Outside the cells:
- Interstitial - outside blood vessels and bathes the cells
- Plasma and transcellular - fluid in spaces such as the brain ventricles,
peritoneal cavity and joints
What is the purpose of the plasma membrane? Provides a hydrophobic barrier separating intracellular and extracellular
components
What sorts of molecules can freely pass the plasma Lipid-soluble molecules, because they dissolve in the phospholipid
membrane? membrane.
What is osmotic pressure? MRT (molarity x gas constant x temperature)
plays an important role in transport of molecules across membranes
depends on the number of particles present per unit volume of solvent
(NOT CHEMICAL MAKE-UP)
What effect do salts have on osmotic pressure? Exert double osmotic pressure as they have two constituent ions
Define osmolarity The number of moles of solute particles per LITRE of solution (preferred
by scientists)
Define osmolality The number of moles of solute per KILOGRAM of solution (preferred by
clinicians)
, What is the value of blood plasma osmolality? precisely 295 mOsmol/kg
(around 300mOsmol/kg)
What makes up blood plasma osmolality? Majority is Na+, Cl- and HCO3-
Glucose contributes around 10 mOsmol/kg
Plasma proteins contribute the least (around 1 mOsmol/kg)
What is meant by isosmotic? Two solutions have the same osmolality.
Why is intracellular and extracellular fluid normally Under normal conditions, the volume of cells is constant so intracellular
isosmotic? fluid has the same osmolality as extracellular fluid.
Fluids which are isotonic are always but Fluids which are isotonic are always ISOSMOTIC but the reverse isn't
the reverse isn't necessarily true necessarily true
What type of cells constantly have to cope with the Erythrocytes (RBCs)
osmotic phenomenon?
What is used to dilute blood and why? 0.9% NaCl solution (rather than pure water) to ensure that cells do not
lyse or crenate.
What is meant by crenation? Water leaves the RBC by osmosis, so it shrinks and shrivels up.
What happens to cells placed in hypotonic The solution is more dilute, so they lyse/burst.
solutions?
What happens to cells placed in hypertonic The solution is more concentrated so the cells crenate.
solutions?
What is meant by tonicity? A relative measure of the osmotic pressure of two solutions on either
side of a semi-permeable membrane.
How does homeostasis enable higher organisms to Because, unlike unicellular organisms, they aren't forced to only live in
survive in and inhabit a range of conditions? places where conditions are correct for that cell as they have greater
control over their body.
What in humans helps maintain homeostasis? The extracellular fluid (extracellular environment is a fluid environment)
Define homeostasis. The maintenance of a constant internal environment within narrow limits
in a wide variety of external environments or conditions.
What does the stability of the extracellular Chemical reactions can occur under optimal conditions.
environment enable?
What are normal internal conditions? [Na+] = 145mM
[K+] = 4mM
temperature = 37.1ºC
pH = 7.4
CORRECT Answers
What limits cell size? Surface area to volume ratio!
Larger cells are less efficient in moving nutrients and waste across the
cell membrane.
As cell size increases, distance for to As cell size increases, distance for TOXINS, IONS, etc. to diffuse from the
diffuse from the nucleus increases. nucleus increases.
What can nano-devices be used for and why? They can interact with the receptors on the surface of cells and inside
cells because they are 100-10,000 times smaller than human cells.
How much of the body's lean mass is water? Around 2/3
What are hydrophilic substances? Ones that are polar (e.g. Na+, glucose, many proteins) and so are able to
dissolve in water
What are hydrophobic substances? Ones that are non-polar (e.g. fats and waxes) so cannot dissolve in water
What are amphiphilic substances? Ones that contain polar and non-polar regions (e.g. phospholipids - have
hydrophilic phosphate head and hydrophobic fatty acid tails)
What is intracellular water? Water found inside the cells: makes up 2/3 of the body's water.
Where is extracellular water found? Outside the cells:
- Interstitial - outside blood vessels and bathes the cells
- Plasma and transcellular - fluid in spaces such as the brain ventricles,
peritoneal cavity and joints
What is the purpose of the plasma membrane? Provides a hydrophobic barrier separating intracellular and extracellular
components
What sorts of molecules can freely pass the plasma Lipid-soluble molecules, because they dissolve in the phospholipid
membrane? membrane.
What is osmotic pressure? MRT (molarity x gas constant x temperature)
plays an important role in transport of molecules across membranes
depends on the number of particles present per unit volume of solvent
(NOT CHEMICAL MAKE-UP)
What effect do salts have on osmotic pressure? Exert double osmotic pressure as they have two constituent ions
Define osmolarity The number of moles of solute particles per LITRE of solution (preferred
by scientists)
Define osmolality The number of moles of solute per KILOGRAM of solution (preferred by
clinicians)
, What is the value of blood plasma osmolality? precisely 295 mOsmol/kg
(around 300mOsmol/kg)
What makes up blood plasma osmolality? Majority is Na+, Cl- and HCO3-
Glucose contributes around 10 mOsmol/kg
Plasma proteins contribute the least (around 1 mOsmol/kg)
What is meant by isosmotic? Two solutions have the same osmolality.
Why is intracellular and extracellular fluid normally Under normal conditions, the volume of cells is constant so intracellular
isosmotic? fluid has the same osmolality as extracellular fluid.
Fluids which are isotonic are always but Fluids which are isotonic are always ISOSMOTIC but the reverse isn't
the reverse isn't necessarily true necessarily true
What type of cells constantly have to cope with the Erythrocytes (RBCs)
osmotic phenomenon?
What is used to dilute blood and why? 0.9% NaCl solution (rather than pure water) to ensure that cells do not
lyse or crenate.
What is meant by crenation? Water leaves the RBC by osmosis, so it shrinks and shrivels up.
What happens to cells placed in hypotonic The solution is more dilute, so they lyse/burst.
solutions?
What happens to cells placed in hypertonic The solution is more concentrated so the cells crenate.
solutions?
What is meant by tonicity? A relative measure of the osmotic pressure of two solutions on either
side of a semi-permeable membrane.
How does homeostasis enable higher organisms to Because, unlike unicellular organisms, they aren't forced to only live in
survive in and inhabit a range of conditions? places where conditions are correct for that cell as they have greater
control over their body.
What in humans helps maintain homeostasis? The extracellular fluid (extracellular environment is a fluid environment)
Define homeostasis. The maintenance of a constant internal environment within narrow limits
in a wide variety of external environments or conditions.
What does the stability of the extracellular Chemical reactions can occur under optimal conditions.
environment enable?
What are normal internal conditions? [Na+] = 145mM
[K+] = 4mM
temperature = 37.1ºC
pH = 7.4
