Draw a labelled diagram that shows the positions of proteins within the cell membrane.

Outline the effects of putting plant tissue in a hypertonic solution.

Explain how the structure of the nephron and its associated blood vessels enable the kidney to carry out its functions.

Phospholipid bilayer drawn and labelled with at least one protein labelled and drawn embedded either in one or both halves of the bilayer

Reject if only peripheral proteins are shown.

Integral/intrinsic/transmembrane/carrier/pump/channel/pore protein labelled and shown crossing the membrane

Extrinsic/peripheral protein labelled and shown on membrane surface/not embedded in bilayer

Glycoprotein labelled and shown integral and with a clear carbohydrate region projecting out on one side of the membrane

The carbohydrate should be shown differently from the protein but need not be labelled specifically.
The protein part can be embedded in one or both phospholipid layers.

Hypertonic solution has more solutes/higher solute concentration «than the tissue/cells/cytoplasm»

Water moves out of the cells/tissue by osmosis «into the hypertonic solution»

Water moves from lower solute concentration to higher solute concentration/up the solute concentration gradient

Reject answers based on water concentrations.

Pressure inside cell drops
OR
cell no longer turgid
OR
cell becomes flaccid

Reject cell decreases in size.
Reject plant wilts and other answers about whole plants.

Volume of cytoplasm drops
OR
«plasma» membrane retracts from the cell wall
OR
cell is plasmolysed

Reject plant cells shrink or shrivel.

Osmoregulation/excretion of nitrogenous waste/urea «is a function of the» kidney

Ultrafiltration in the glomerulus/smaller molecules filtered out in the glomerulus
OR
capillary walls/glomerulus permeable to smaller molecules
Reject ultrafiltration in the Bowman’s capsule.

Basement membrane/filtration slits/podocytes act as filter/prevent loss of «large» «proteins»/prevent loss of blood cells

High «blood» pressure in glomerulus due to larger afferent than efferent arteriole

«Selective» reabsorption of glucose/useful substances in proximal convoluted tubule

Microvilli/coiling/convolutions give large surface area
OR
pump proteins to reabsorb specific solutes «in proximal convoluted tubule»

Water reabsorbed in descending limb «of loop of Henle»
OR
descending limb permeable to water

Active transport/active pumping of sodium ions/Na⁺ out of ascending limb «from filtrate to medulla»

Ascending limb is impermeable to water

Loop of Henle creates solute gradient/high solute concentration/hypertonic conditions in medulla

Distal convoluted tubule adjusts pH/adjusts concentration of Na⁺/K⁺/H⁺

Water reabsorbed in collecting duct

Collecting duct permeability to water varies due to number of aquaporins/ADH

Osmoregulation by varying the amount of water reabsorbed «in the collecting duct»

There were many neat and accurate diagrams of membrane structure showing a variety of proteins. It was not difficult to earn the three marks. Peripheral proteins should be shown on the surface of the phospholipid bilayer, not embedded in it.

This part was less well answered, with candidates failing to make the basic points about the events caused by putting plant tissue into a hypertonic solution. Some candidates misunderstood the term ‘tissue’ and talked instead about placing whole plants in a solution. Candidates should be careful to state that hypertonic means a higher solute concentration, not just a high concentration. Explanations of osmosis in terms of water concentration should be discouraged as there are no units for measuring such concentrations. Water potential terminology is not expected as it is not part of the new programme.

Answers to this question were very varied. The functions expected were osmoregulation and excretion thus the focus should have been on how the nephron can vary the volume and concentration of urine so as to bring the blood back to normal levels, and on how waste products can be concentrated in urine to conserve water. Some teachers commented on G2 forms that is was unreasonable to expect details of the structure of associated blood vessels but all that was required was the structure of the glomerulus. Able candidates who had prepared carefully were able to score highly but weaker candidates tended to be very muddled.