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AS Human Biology Unit 2
Text questions
| P22/Q1 |
Raw materials: O2, H2O, ions. Waste products: CO2, urea. |
|
| P23/Q2 |
Very thin. |
|
| P23/Q3 |
The environments on the both sides of the membrane
are aqueous, hence hydrophilic heads on the outside
of the phospholipid bilayer. Hydrophobic tails on
the inside because they are repelled by water
molecules outside the phospholipid bilayer and, at
the same time, are attracted by hydrophobic tails of
the opposite layer of phospholipid molecules. |
|
| P23/Q4 |
Since sideways movements of phospholipid molecules
are reduced, the diffusion of O2 & CO2 will be
slowed down (due to smaller gaps between
phospholipid molecules which are "glued" together by
cholesterol). |
|
| P26/Q5 |
Diffusion rate across B could be faster than the D
rate across A if the concentration gradient
(for tissue B) was higher/steeper. |
|
| P26/Q6 |
Tissue A
→ thinner
surface
→ faster
diffusion Tissue B → thicker surface → slower diffusion Tissue C → larger surface area → faster diffusion |
|
| P27/Q7 | a) b) |
Lipid-soluble molecules can diffuse across the
membrane because their properties are similar to the
properties of lipids (hydrophobic), hence they will
diffuse through hydrophobic part of the bilayer
easily. Small molecules (eg. O2, CO2) can diffuse easily across the membrane, because spaces between phospholipid molecules is likely to be larger than the size of these small molecules. |
| P29/Q8 | a) b) |
P(-1kPa) → Q(-4kPa) S(0kPa) → R(-1kPa) |
Assignment
| P34/Q1 | A: Water + dissolved substances are filtered out
from blood into the cavity of the nephron (→filtrate). B: Glucose reabsorbed from the filtrate back into the blood. |
|
| P34/Q2 | Active transport is involved in the reabsorption of
glucose at B, because glucose molecules are
transported against the concentration gradient. Microvilli: increase surface area over which reabsorption takes place effectively speeding up the process Mitochondria: provide ATP (from respiration) needed for the process of reabsorption (active transport). |
|
| P35/Q3 | a) b) |
Concentration of molecules of urea is higher in
the blood than in the dialysis fluid
→ molecules of urea move
down the concentration gradient by diffusion. Only excess ions are removed. Once an equilibrium has been reached there is no net movement of the ions between blood and dialysis fluid. |
| P35/Q4 | Semipermeable membrane has pores which are
smaller than the size of RBC as well as larger
molecules (proteins), hence RBC & these large
molecules do not diffuse. |
|
| P35/Q5 | Total surface area of a large number of small
tubes is larger than a smaller number of much larger
tubes. Rate of diffusion (→Fick's Law) is directly proportional to the surface area over which diffusion takes place. |
|
| P35/Q6 | CAPD (Continuous Ambulatory Peritoneal
Dialysis) is an ambulatory
method of dialysis. Excess urea in
the blood is diffusing continuously
(for several hours) across semi-permeable membrane
called peritoneum, which surrounds
organs in the abdominal cavity. |
|
| P35/Q7 | Extra glucose will lower Water Potential (WP) of
the dialysis fluid in comparison with the WP of the
blood → net movement of water from the blood to the fluid will follow. |
Examinations
| P36/Q1 | a) |
(i) -7 Mpa (ii) A (-7 MPa) → B (-12 MPa), C (-4) → A (-7), C (-4) → B (-12) (iii) WP of distilled water is 0. Addition of a solute (eg. sucrose) to water decreases WP of the solution, so WP is expressed using negative numbers. |
| b) |
(i) Glycerol is an example of an uncharged molecule.
Permeability to this sort of molecules is not
affected by the presence of phosphate groups (which
are charged groups) in the biological membrane. This
is why there is no difference between the
permeability of a lipid artificial membrane and a phospholipid (biological) membrane to glycerol. (ii) Sodium ions (Na+) are positively charged, but phosphate groups in a phospholipid bilayer (biological membrane) are negatively charged. (+) and (-) attract each other, hence permeability of a phospholipid (biological) membrane to Na+ is higher than permeability of a lipid artificial membrane (which is made of uncharged molecules) to Na+. There are special protein molecules spanning across the biological membrane called ion channels which allow Na+ to pass through, hence increasing the biological membrane's permeability to the ions. Ion channels are not present in the artificial membrane. |
|
| P36/Q2 | a) |
(i) High magnification at high resolution. (ii) Microvilli of epithelial cells damaged by E. coli. |
| b) |
Fick's law: Rate of diffuion = (Surface Area x Difference in Concentration) / Distance Microvilli increase the surface area (SA) of the
small intestine available for diffusion of glucose. |
