VCE Food Studies Practice Questions

(a) Protein digestion and absorption — using salmon: Protein digestion begins in the stomach, where the enzyme pepsinogen is secreted by chief cells of the gastric mucosa and activated to pepsin by hydrochloric acid (HCl). Pepsin is an endopeptidase that cleaves peptide bonds within the polypeptide chains of salmon protein, producing shorter polypeptides. The partially digested protein then moves into the small intestine (duodenum), where the pancreas secretes protease enzymes — trypsin, chymotrypsin, and elastase (all endopeptidases) — via the pancreatic duct. These enzymes further break polypeptides into smaller peptides. Exopeptidases (carboxypeptidase from the pancreas; aminopeptidase and dipeptidase from the brush border of intestinal villi) then cleave individual amino acids from the ends of peptide chains until single amino acids and di/tripeptides remain. Absorption occurs primarily in the small intestine (jejunum). Amino acids are absorbed by active transport (sodium-dependent co-transport) across the brush-border membrane of enterocytes. Di- and tripeptides are transported by PepT1 carriers and hydrolysed inside the enterocyte. Amino acids then pass across the basolateral membrane into the hepatic portal blood supply and are transported to the liver. (b) Both starch and dietary fibre are polysaccharides made up of glucose monomers joined by glycosidic bonds. However, their structural difference is in the type of bond: — Starch (amylose/amylopectin) contains alpha-1,4 and alpha-1,6 glycosidic bonds. — Dietary fibre (e.g. cellulose) contains beta-1,4 glycosidic bonds. Humans produce the enzyme amylase (salivary and pancreatic), which can only hydrolyse alpha-1,4 glycosidic bonds. There are no human enzymes capable of breaking beta-1,4 bonds; therefore cellulose passes through the gastrointestinal tract undigested and unabsorbed, reaching the large intestine intact where it provides bulk and feeds gut microbiota. (c) Two functions of lipids from olive oil dressing: 1. Energy provision — lipids are the most energy-dense macronutrient, providing approximately 37 kJ per gram, serving as a concentrated energy store. 2. Absorption of fat-soluble vitamins — dietary fat is required for the absorption of fat-soluble vitamins A, D, E and K from the small intestine; without fat, these vitamins cannot be incorporated into micelles for absorption.