Explain the mechanisms used by the ileum to absorb and transport food.

absorption occurs through epithelial cells on villi/tiny projections;
microvilli/brush border on cell membrane increase surface area;
tight junctions prevent leakage of nutrients;
lipids/fat soluble/non-polar substances diffuse across membranes;
converted into tryglicerides / coated with proteins to form chylomicrons/lipoproteins;
which enter into lacteals/lymphatic system by exocytosis;
fructose/hydrophilic food enters by facilitated diffusion/through channel proteins;
active transport requires ATP (from many mitochondria in cells) / against concentration gradient through pump proteins;
e.g. glucose/amino acids/minerals enter through co-transported sodium carriers;
endocytosis of large molecules (e.g. vitamin B12) / pinocytosis of liquids;
capillaries (close to epithelial cells) transport substances (to body via bloodstream);

Most candidates gained a range of marks for this question, but most answers lacked enough precision to gain all of them, being limited to generalities about absorption and transport of nutriments by the ileum and/or addressing only core assesment statements instead of option H's. Many candidates used inappropriate terminology (e.g. membrane instead of epithelium; blood vessel when capillary is meant) and limited themselves to stating factual knowledge without providing an actual explanation of the mechanisms (e.g. glucose is actively transported through sodium carriers). Many students reported epithelial cells having pinocytic vesicles to absorb various types of molecules, not realizing that these vesicles are the result of endocytosis and not the cause.