Stem cells are found throughout the human body. Lgr5+ stem cells are found in the lining of the small intestine. Fig. 2.1 is a flow chart showing stages in the development of one of the daughter cells produced by the mitotic division of an Lgr5+ stem cell. [Figure 2.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

1. any two from:
2. [1] to, replace (old / worn-out / dead / short-lived) cells / repair (damaged) tissue ; I repair cells
3. [1] stem cells divide and, differentiate / become specialised ; A form different types of cells
4. [1] idea of self-renewal e.g. stem cells divide to maintain the, pool / number, of stem cells ; I increase in number of stem cells
5. [1] AVP; ref. to movement of food through intestine / presence of pathogens, increases chance of damage cells (produced by stem cells) are genetically identical so the function of, the intestine / organs / tissues, can continue / AW idea that allows growth (of small intestine) during development / AW R growth of cells
6. [1] anaphase ;
7. [1] cytokinesis ;
8. any two from
9. [1] (two) sister/identical, chromatids attached together ; R 'sister chromosomes' A holds the chromatids together after, replication / S phase
10. [1] attach (chromatids / chromosomes) to spindle (fibres) ; in context of mitosis R if stated in interphase A kinetochore or spindle microtubules for spindle (fibres)
11. [1] (centromeres) divide / separate, (at the start) in anaphase ; A end of metaphase
12. [1] so daughter chromosomes can be moved to opposite poles; A sister / identical, chromatids do not award MP4 unless MP3 already given
13. look for function in explanation if not on first line for each cell one mark for the function and one mark for the explanation mark each cell straight through to max 2
14. Cell P: function: absorption / uptake / movement in, of, (named) substances / nutrients OR diffusion of, (named) substances / nutrients OR active uptake / active transport, of (named) substances / of nutrients OR breakdown of food molecules OR production / secretion, of enzymes
15. Cell P: explanation: microvilli, to give a large surface area / increase surface area / increase number of transport proteins (for uptake of digested food) OR I cilia have large surface area A large surface area:volume ratio for microvilli OR mitochondria to provide, ATP / energy, for, active transport/active uptake R produce / make, energy R energy for cilia OR large surface of membrane for enzymes for digestion OR microvilli for membrane enzymes / RER for making enzymes / Golgi for packaging enzymes or modification of enzymes
16. Cell Q: function: secretion / release / exocytosis / AW, of mucin / mucus I produce and provide if Q is secreting protein/unnamed substance allow ECF for explanation
17. Cell Q: explanation: rough endoplasmic reticulum for making protein (part of mucin / mucus) OR Golgi body for, packaging / glycosylating / modification / AW, mucin A mucus AW = adding carbohydrate / sugars OR (large) vesicles / vacuoles, for storage / for containing / for transport, of mucin A mucus
18. Cell R: function: secretion / release / exocytosis / move ment out / AW, of (named) protein(s) I produce and provide A hormones / peptides / enzymes
19. Cell R: explanation: (large quantity of) RER for, making proteins / making enzymes/translation / AW OR Golgi body for packaging / modification / AW, proteins OR vacuoles / vesicles, for transport to cell surface membrane / release by exocytosis / fusion with cell surface membrane