The liver receives blood from the hepatic artery and from the hepatic portal vein. The hepatic portal vein transports blood from the digestive system. Hepatocytes are the main cell type of the liver. They have a wide range of functions, including: • the synthesis of triglycerides and plasma proteins • detoxifying waste • energy storage.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

1. [1] aorta / dorsal aorta; correct spelling needed
2. [1] any one from: context is using gaps for movement between, hepatocyte/tissue fluid, and, blood/sinusoid I ref. to red blood cells I shorter diffusion, distance / pathway
3. [1] higher rate of / easier for / AW, exchange / movement / AW, of substances; A named substances / nutrients
4. [1] substances do not have to cross, a cell layer/into and out of endothelial cells ;
5. [1] larger molecules / plasma proteins, can pass through;
6. [1] Kupffer cells can pass through (into tissue fluid); AW A ref. to other phagocytic cells R Kupffer cells can diffuse through R if stated as entering hepatocytes
7. [4] max 3 if described as phagocytosis of a pathogen rather than a red blood cell allow rbc for red blood cell
8. [4] any four from: 1 endocytosis / phagocytosis;
9. [4] 2 described; e.g. red blood cell, engulfed / enveloped pseudopodia surround red blood cell
10. [4] max three from 3 forms (phagocytic) vacuole / (phagocytic) vesicle / phagosome ;
11. [4] 4 lysosome fuses (with phagosome) ; AW merges / joins to / combines with I attaches / binds to
12. [4] 5 (lysosome contains) hydrolytic / digestive, enzymes ; A hydrolases / named examples
13. [4] 6 digestion to produce haem and globin; A amino acids for globin
14. [4] 7 AVP; e.g. suggestion of, detection / recognition, of red blood cell
15. [3] any three from: I Golgi body / lysosome / vesicle
16. [3] mp1 and mp2 complete term needed either in the text or labelled 1 smooth endoplasmic reticulum labelled on Fig. 3.2 and detail; e.g. for, lipid / triglyceride / cholesterol, synthesis tubular appearance / no ribosomes
17. [3] 2 rough endoplasmic reticulum labelled on Fig. 3.2 and detail; e.g. for protein, synthesis / AW A for enzyme synthesis flattened (sac) appearance ribosomes A ribosome(s) labelled and for (plasma) protein synthesis
18. [3] 3 mitochondrion labelled on Fig. 3.2 and detail; e.g. many mitochondria for (aerobic) respiration produce ATP / provide energy, (for hepatocyte reactions) R generate/make, energy double membrane / presence of cristae allow if one mitochondrion is correctly labelled and one of the ‘circular' mitochondria has a different label e.g lysosome
19. [3] 4 presence of glycogen granule(s) as, energy / glucose, store ; A releases/ provides, glucose
20. [3] 5 presence of lipid droplet(s), as energy store ; A provides fatty acids A provides components for cholesterol synthesis
21. [3] penalise once (from mp1, 2, or 3) if diagram not labelled but structures named correctly and correct detail given
22. [1] any one from: I ref. to staining or size
23. [1] mitochondrion, bound by / has, double membrane / two membranes ; I peroxisome has (only) one membrane
24. [1] peroxisome no cristae / mitochondrion has cristae ; R cisternae
25. [1] peroxisome spherical shape and mitochondria, different shapes / AW ; I if only peroxisome shape stated A circular for spherical A description e.g. 'sausage' shape
26. [2] any two from: mitochondrion (ora for peroxisomes) has, DNA/genes (coding for enzymes) ; R linear DNA A genetic, material / information, qualified with, transcription / ref. to mRNA / coding for enzymes
27. [2] (70S) ribosomes (site of enzyme synthesis) ; R 80S ribosomes
28. [2] has the enzymes for, transcription / translation, (to synthesise enzymes);
29. [2] can produce ATP (for enzyme synthesis) ; R produce energy I has ATP
30. [2] AVP; ; other suggestions e.g. has (chaperone) proteins involved in, folding / formation of tertiary structure ATP cannot enter peroxisome to provide energy source peroxisome has enzymes that cause degradation of, one / or more, substance(s) involved in protein synthesis
31. [2] any two from: (peroxisome) membrane bound, so rest of cell protected (from hydrogen peroxide) ; A hydrogen peroxide can have toxic effects on (rest of) cell / AW
32. [2] (peroxisome) acts as a compartment / specific area / contained, for, more efficient breakdown of hydrogen peroxide / control of reactions ;
33. [2] high concentration of enzyme in one location ; A more enzyme-substrate complexes can form
34. [2] provides, optimum / AW, conditions, for (other peroxisome) reactions ;
35. [2] production of oxygen as by-product, so useful for, peroxisome reactions requiring oxygen / mitochondrial function / aerobic respiration;
36. [2] AVP; e.g. isolates (peroxisomes) enzymes from rest of cell