The wall of the small intestine is highly folded to form villi. Between the villi are infoldings known as crypts of Lieberkühn. Fig. 1.1 is a diagram of a section through a single villus and a crypt of Lieberkühn. [Figure 1.1] Fig. 1.1 shows that the epithelium of the villus contains mainly goblet cells and cells known as enterocytes. Both cell types have microvilli on the apical surface (surface facing the gut lumen). Goblet cells are involved in the production of mucus. Enterocytes are adapted for the absorption of the soluble products of digestion. These products enter the circulatory system.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

1. [2] any two from: / cilium composed of microtubules / microvillus, composed of microfilaments / contains actin (filaments) ; / or / cilium 9+2 (microtubule) arrangement ; / cilium has basal body; A has centrioles at the base / cilium shows synchronous, rhythm / movement ; A whip-like / rhythmic, movement / cilium, moves / wafts, mucus / or / microvillus increases, surface area / SA, for, absorption / uptake / secretion ; A increases SA to locate transport proteins AW / 6 AVP; e.g. cilium has dynein (arms) / cilium is, longer (10 µm) / wider (0.2 µm) or microvillus is, shorter (1 µm) / narrower (90 nm)
2. [1] any one from: / protects (intestinal), epithelium / cells / lining ; / A examples of protection e.g. damage from stomach acid / digestion by enzymes / A less likely for epithelial cells to be damaged / AW / A traps, pathogens or (harmful), bacteria / microbes / microorganisms / I dust / A prevents, pathogens / AW, from reaching cells / eases / reduces friction for, movement of, gut contents / substances (through digestive system) ; / habitat / nutrient source, for gut, microorganisms / flora ; AW / AVP; e.g. location for immune system cells / R if stated as being in the gas exchange system
3. [1] arteriole; A (small) artery
4. [2] any two from: / (at arteriole end of capillary) high, hydrostatic / blood, pressure ; / A ref. to hydrostatic pressure gradient / (ultra)filtration / described ; e.g. fluid / plasma/ water and solutes, forced / comes out of, capillaries / blood / glucose / amino acids / ions, leave (blood) or (large / plasma) proteins remain (in blood); / R if stated, red blood cells / platelets, leave / through, fenestrations / fenestrae / endothelial pores / or / pores/gaps/spaces, in, capillary wall / endothelium / between cells ;
5. [3] any three from: / after, secreted / released, by enteroendocrine cells / transport of, peptide / GLP-1 / ligand, in, blood / circulation ; / to, target cells (which are cells of the, stomach / pancreas) ; / binding of, peptide / GLP-1 / ligand, to receptor ; context can be cell surface membrane or intracellular / ref. to, specificity / complementary ; must be in correct context of GLP-1 binding to receptor / (binding) triggers / sets off / AW, events within (target) cell (e.g. signal transduction / triggers enzyme cascade) ;
6. [1] prophase / metaphase / anaphase / telophase ; / R if interphase or cytokinesis stated
7. [3] any three from: / presence of, vesicles / vacuoles, qualified ; e.g. many / secretory / Golgi / A storage vesicles / correct ref. to exocytosis; / A fusion of, vesicle / vacuole, with cell surface membrane / much / high proportion of / a lot of / AW, rough endoplasmic reticulum ; / I ER / RER / rough ER / A many ribosomes / ref. to nucleus/nucleolus, is neutral / rough endoplasmic reticulum / ribosomes, site of, peptide / polypeptide / protein / enzyme, synthesis ; / ecf for abbreviating rough endoplasmic reticulum previously / AVP; e.g. presence of mitochondria to provide, ATP / energy, for, protein synthesis / movement of vesicle to cell surface membrane / exocytosis mp2 can also be awarded here only if ref. has been made within response to vesicles / vacuoles
8. [1] Paneth cell is, differentiated/specialised (for, secretion / its function) / or / stem cells are, undifferentiated/not differentiation / not specialised;