The alimentary canal, in order
Alimentary canal — one continuous tube from mouth to anus, in a fixed order: mouth (ingestion, chewing) -> oesophagus (muscular tube to the stomach) -> stomach (churns food with digestive juices) -> small intestine, the duodenum first then the longer ileum (most absorption) -> large intestine, the colon (absorbs water), then the rectum (stores faeces), then the anus. Diagrams often give position only, so learn the sequence, not just the names.
The four associated organs
Associated organs — four organs that food never passes through, but which supply juices to the canal. Salivary glands release saliva into the mouth. Pancreas, behind the stomach, releases pancreatic juice into the duodenum. Liver produces bile. Gall bladder stores that bile and releases it into the duodenum when food arrives. How bile then acts on fat belongs to B7.3, not here.
The five named processes
Five processes, each with a two-element mark-scheme definition. Ingestion = the taking of substances into the body. Digestion = the breakdown of food into smaller molecules. Absorption = the movement of nutrients from the intestines into the blood. Assimilation = the uptake and use of nutrients by cells. Egestion = the removal of undigested food as faeces. They run in that order, matching the journey of food.
Drawn from real examiner reports.
The pancreas absorbs nothing
The pancreas is drawn close to the intestines, so candidates hand it an absorption job. It is an associated organ: it releases pancreatic juice into the duodenum and absorbs nothing at all. Water absorption from the gut contents is a function of the large intestine (colon). Keep the pancreas to secretion only.
Flagged Jun 2022 P11 Q6
Liver makes bile, gall bladder stores it
The liver produces bile; the gall bladder only stores it and releases it into the duodenum when food arrives. So "which organ produces bile?" answers liver, and "which organ stores bile?" answers gall bladder. Crediting the gall bladder with making bile is a repeated Core-level error.
Absorption must reach the blood
"Nutrients are taken up" earns nothing. The mark scheme wants both elements: what moves (digested, small, soluble food molecules) and where to — across the wall of the small intestine and into the blood. A vague one-element phrase is the commonest way to lose this definition mark.
Flagged Nov 2023 P31 Q7c
Absorption is not assimilation
Absorption is nutrients crossing the intestine wall into the blood. Assimilation is the next stage — cells taking up and using nutrients that are already in the blood. Glucose crossing into the blood in the ileum is absorption; a liver or muscle cell using that glucose to release energy is assimilation.
Egestion is not excretion
Egestion removes undigested food as faeces through the anus — material that was never inside the body cells or the blood. Excretion (not part of B7.2) removes the waste products of the body's own metabolism, such as carbon dioxide and urea. Both end with something leaving the body, but they are different processes.
Duodenum first, ileum second
Both are parts of the small intestine and are routinely swapped. The duodenum comes first and receives bile and pancreatic juice; the ileum follows and is the main site of absorption. Answering "small intestine" and "large intestine" when the question asks for the named sub-parts also loses marks.
Name, classify, then state the process
Answer every organ question with the same chain: name the organ precisely (duodenum, not just small intestine) -> classify it as an alimentary canal organ or an associated organ -> state which of the five named processes it carries out.
Fix the order before you label
On an unlabelled diagram, lay out the sequence first — mouth, oesophagus, stomach, duodenum, ileum, colon, rectum, anus — with the salivary glands, pancreas, liver and gall bladder placed around it. Naming organs before fixing the order is how the duodenum and ileum get swapped.
Use the named process word
"Which process is happening here?" tests one skill: mapping a described event onto ingestion, digestion, absorption, assimilation or egestion. A long descriptive answer scores nothing if the named process word never appears in it.
Percentage-absorbed calculations
Divide the mass absorbed by the mass ingested, then multiply by 100. If the data give the mass egested instead, subtract it from the ingested mass first. The usual slips are dividing the wrong way round, and giving the percentage egested when absorbed was asked for.
Cambridge 0654 spec reference: Section B7 "Human nutrition", sub-topic B7.2 (Core only in this leaf — no Supplement). This leaf covers identifying the main organs of the digestive system in diagrams and images, and describing their functions in relation to ingestion, digestion, absorption, assimilation and egestion. The chemistry of digestion (enzymes, hydrochloric acid, bile's mechanism) is covered separately in B7.3.
The alimentary canal is one continuous tube, in this order:
| Order | Organ | Notes |
|---|---|---|
| 1 | Mouth | Ingestion begins here; food is chewed |
| 2 | Oesophagus | Muscular tube carrying food to the stomach |
| 3 | Stomach | Muscular bag; churns food, mixes it with digestive juices |
| 4 | Small intestine — duodenum | First, shorter section; receives bile and pancreatic juice |
| 5 | Small intestine — ileum | Longer section; site of most absorption |
| 6 | Large intestine — colon | Absorbs water from undigested remains |
| 7 | Large intestine — rectum | Stores faeces before egestion |
| 8 | Large intestine — anus | Where faeces leave the body (egestion) |
Four associated organs (food does not pass through these, but they contribute to digestion):
| Associated organ | Function |
|---|---|
| Salivary glands | Release saliva into the mouth |
| Pancreas | Releases pancreatic juice into the small intestine (duodenum) — it does not absorb water |
| Liver | Produces bile |
| Gall bladder | Stores bile (made by the liver) and releases it into the duodenum |
The five named processes (each has a precise, two-element definition):
Define (a) ingestion and (b) egestion.
A diagram of the human digestive system shows the alimentary canal as a continuous tube from the mouth to the anus, with eight labelled positions along it.
State the name of the organ found at each of the eight labelled positions, in the correct order from mouth to anus. (4 marks)
