Draw a labelled diagram showing the structure of three water molecules and how they interact.

Aquatic and other environments are being affected by a global rise in temperature. Outline the consequences of this on arctic ecosystems

Cell membranes separate aqueous environments in cells. Explain how the properties of phospholipids help to maintain the structure of cell membranes.

a. O connected to 2 H forming a V shape;
b. line between O and H of same molecule labelled as covalent bond;
c. three water molecules bonded together with dashed/dotted lines between O on one molecule and H on another;
d. dotted/dashed line labelled as hydrogen bond;
e. O labelled as partial negative charge/  and H labelled as partial positivecharge/  ;

a. warming results in melting (arctic/polar) ice (cap) / loss of ice habitats;
b. (warming) raises sea level / floods coastal areas / destroys coastal habitats;
c. (warming) of habitat would change species/flora/fauna that can be supported (named examples can be used);
d. decrease in size of population(s) / possible extinction of species;
e. temperate species move into area / arctic species adapt/move;
f. change in distribution of species/changes in migration patterns;
g. (ecological) changes will affect higher trophic levels/food webs/food chains;
h. increased rates of decomposition of detritus from (melting) permafrost;
i. increased success of pest species including pathogens;

a. (labelled) phospholipid consisting of head and two tails;
b. head is glycerol and phosphate;
c. tails are fatty acid chains;
d. head hydrophilic and tails hydrophobic;
e. hydrophilic molecules/heads attracted to/soluble in water;
f. hydrophobic molecules/tails not attracted to water but attracted to each other;
g. (properties of phospholipids leads to) formation of double layer in water;
h. stability in double layer because heads on outer edge are attracted to water and tails are attracted to each other in middle;
i. phospholipid bilayer in fluid/flexible state because of attraction of non-polar tails to each other;
j. (fluidity) allows membranes to change shape/vesicles to form or fuse with membrane/(fluidity) allows cells to divide;
k. non-polar amino acid side chains attracted to (hydrophobic) tails;
Marks may be earned using suitable labelled/annotated diagrams illustrating the points given above.

(Plus up to [2] for quality)

Almost all candidates knew the V shape for water molecules but few labeled covalent bonds and still fewer were exact in describing the negative charge on O as partial or the positive charge on H as partial. The mark scheme assumes a stick model of water. Answers often used a bubble diagram, undercutting one possible mark. Even so, full marks could be earned. Bonding within and among water molecules was the part most often neglected.

This question was generally well answered displaying good knowledge of the effect of global warming on arctic ecosystems. Often this answer was reasonably well started, but often did not have enough follow-through. Weak answers included some odd understandings. It is not melting glaciers that are the issue, it is the melting ice cap and the sea ice. Some answers were glib, repeating the cases made by the public media rather than research-based information regarding the plight of endangered animals. There are no penguins in the Arctic.

This question expected students to approach the topic from a slightly different position than the usual. As such, it discriminated well between stronger and weaker candidates. Many students misinterpreted what was being asked and wrote long detailed answers on structure of the cell membrane and how transport occurs through the proteins - rather than concentrating on the properties of the phospholipids which give the cell membrane its structure. Answers needed more attention to interaction of phospholipid with water. Few knew that the phospholipid head is glycerol and phosphate and virtually nobody mentioned anything about non-polar amino acid side chains being attracted to (hydrophobic) tails.