Outline four types of membrane transport, including their use of energy.

Draw the structure of a dipeptide.

ADH (antidiuretic hormone) is a peptide hormone that is produced in the hypothalamus. Explain its action in the human body.

a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔

b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔

c. osmosis is the passage of water through a membrane from lower solute concentration to higher ✔ OWTTE

d. active transport is movement of molecules/ions against the concentration gradient «through membrane pumps» with the use of ATP/energy ✔

e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy
OR
exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔

f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔

mpa, mpb and mpc require reference to concentration.  

Active transport requires mention of the use of energy.

a. two amino acids, one with NH₂/NH₃+ end and one with COOH/COO– end ✔

b. peptide bond between C=0 and N—H correctly drawn ✔

c. «chiral» C with H and R group on each amino acid ✔

d. peptide bond labelled/clearly indicated between C terminal of one amino acid and N terminal of the second amino acid ✔

Labels not required for amino group and carboxyl group.

a. ADH plays a role in osmoregulation/regulating blood solute concentration ✔

b. acts on the collecting ducts of the kidney ✔

c. acts in «late» distal convoluted tubule ✔

d. hypothalamus detects plasma/blood osmolarity/solute concentration ✔

e. if plasma/blood is too concentrated/hypertonic, «posterior» pituitary releases ADH ✔

f. ADH stimulates insertion of aquaporins/water channels / increases permeability of collecting duct ✔

g. water moves «through aquaporins» by osmosis into the medulla/blood ✔

h. urine becomes more concentrated/smaller volume ✔

i. negative feedback occurs ✔ OWTTE for negative feedback acceptable.

j. if blood is hypotonic no ADH is released ✔

k. water is not reabsorbed from the collecting ducts/permeability of the collecting duct decreases ✔

l. urine becomes more dilute/less concentrated / higher volume ✔

OWTTE for all mp.

Question 6 was the most popular extended response question. It was less common for students to correctly describe endocytosis and exocytosis. A common misconception was for students to describe both types of bulk transport as passive processes when they both require energy. Students also commonly failed to make reference to concentration gradients in their discussions of active and passive transport.

Students were successful at indicating the presence of two chiral carbons. Commonly the carboxyl group was represented as an aldehyde group. Nitrogen atoms were commonly shown as having just two bonds.

This question was commonly very well answered. Common errors included muddling the roles of the hypothalamus and the pituitary gland in the production and release of ADH. It was uncommon for students to include a discussion of negative feedback in their answers.