IP Biology Upper Sec 04: Nutrition in Humans

These notes align with SEAB GCE O-Level Biology (6093) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 — scope unchanged; remains the reference for this note.

What you must know

• Digestive organs: mouth (mastication, saliva amylase), oesophagus (peristalsis), stomach (acid, protease/pepsin), small intestine (bile, pancreatic enzymes, intestinal enzymes), large intestine (water absorption), rectum/anus (storage/egestion).
• Enzymes: amylase → maltose; maltase → glucose; protease/trypsin → peptides/amino acids; lipase → fatty acids + glycerol; bile emulsifies fats (mechanical).
• Villi: large surface area (folds, microvilli), thin epithelium, rich capillary network, lacteal for fats; hepatic portal vein carries absorbed sugars/amino acids to liver.
• Liver roles: regulates blood glucose (glycogen storage/breakdown), deaminates amino acids → urea, detoxifies alcohol/drugs, produces bile.
• Alcohol effects: short term (slower reaction, impaired judgment), long term (fatty liver, cirrhosis); social/legal impacts.

Detailed notes

• Digestive workflows: mechanical (chewing, churning) increases surface area; chemical digestion uses enzymes with pH optima—pepsin at low pH, pancreatic/intestinal enzymes at neutral/alkaline pH (bile + pancreatic hydrogencarbonate neutralise chyme).
• Enzyme sites: salivary amylase (starch → maltose) in mouth/esophagus until stomach acid inactivates; pepsin/trypsin/peptidases break proteins; lipase splits fats; maltase/sucrase/lactase finish carbohydrate digestion at intestinal brush border.
• Bile: produced by liver, stored in gallbladder, released into duodenum; emulsifies fats into micelles to speed lipase action; provides alkaline medium.
• Villi and absorption: capillaries take glucose/AA via hepatic portal vein to liver (excess glucose → glycogen; amino acids for protein synthesis or deamination). Lacteals take fatty acids/glycerol as chylomicrons into lymph before returning to blood.
• Assimilation: glucose for respiration/glycogen; amino acids for growth and repair; lipids for membranes/energy storage. Large intestine reclaims water, forming faeces; gut flora aid vitamin production.
• Liver detox: converts alcohol to acetaldehyde then acetate; excessive intake causes fatty liver → hepatitis → cirrhosis; stores vitamins A, D, B12 and iron (as ferritin); forms urea via deamination.
• Peristalsis mechanics: circular muscles contract behind bolus, longitudinal muscles contract ahead to shorten path; continues in all gut sections.

Quick applications

• Trace a meal: starch → maltose in mouth (amylase), proteins begin in stomach (pepsin, acidic pH), in duodenum pancreatic amylase/trypsin/lipase + bile; in ileum maltase/peptidases complete digestion; absorption in ileum; water in colon.