Outline factors that can lead to an individual becoming obese.

Amino acid polarity is an important factor in determining the functions of proteins. Explain the importance of polar and non-polar amino acids in membrane proteins.

diet rich in carbohydrate/fat;
too much food intake / unbalanced diet / food cheap and readily available;
sedentary lifestyle / lack of training/exercise;
genetic disposition/disorder;
malfunction of hunger centre;

polar amino acids are soluble/have stable interactions in water/extracellular fluid/cytoplasm;
non-polar amino acids are soluble/have stable interactions in the lipid bilayer;
polar amino acids strongly hydrophilic and non-polar amino acids are repelled by water/are hydrophobic;
(help to) retain protein in position in the membrane;
polar amino acids form hydrophilic channels/protein pores in membranes;
transmembrane proteins have polar amino acids on either side of the membrane;

There were some good answers by the majority of students, with many gaining three marks. Interestingly, few suggested a malfunction of the hunger centre, which was an acceptable alternative.

The understanding of many candidates was insufficient to answer this question, and it proved to be a good discriminator. Often students were writing about proteins rather than amino acids.