There is a global shortage of blood for transfusions. Researchers can culture bone marrow stem cells in the laboratory to manufacture red blood cells for potential use as an artificial blood product. The researchers collect bone marrow stem cells that are present in small quantities in blood, rather than extracting them from bone marrow. • Antibodies, specific to bone marrow stem cells, are attached to tiny magnetic beads. • The beads are added to a sample of blood. • An electric field is applied to immobilise the beads so that the bone marrow stem cells can be collected.

Mark scheme

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

1. [1] antigen(s)
2. [1] (origin from bone marrow so) haematopoietic / results (only) in production of blood cell types ; A specialise / differentiate, into red blood cells
3. [1] able to produce genetically identical cells
4. [1] (retain ability to) divide (continuously) / carry out mitosis / go through cell cycles ; I reproduce / replicate
5. [1] (so) large numbers (of red blood cells) can be produced ; A can, produce stem cells / self-renew R can differentiate into stem cells
6. [1] can avoid passing on diseases / AW
7. [1] less invasive than extraction from bone marrow ; AW ora
8. [1] immobilisation method used to collect the stem cells is, only possible if in blood / easy / easier (than extraction from bone marrow) ; ora
9. [1] AVP ; e.g. can replace blood taken as a sample by a transfusion easily genetically modified can be modified to avoid rejection
10. [1] no toxic effects (in recipient)
11. [1] should not stimulate an, allergic / immune, response (in the recipient) ; A not rejected
12. [1] does not carry any pathogens / AW ; A no risk of infection / named example A screening (of blood product) not required
13. [1] long shelf life / long-lasting ; A easy to store
14. [1] can transport oxygen ; A idea of improved ability to carry / transport / deliver, oxygen
15. [1] soluble, in blood or idea of able to circulate easily in blood
16. [1] used for all blood types / specific to particular blood types
17. [1] AVP ;; e.g. can carry out other functions of blood fast production / large quantities / mass production acceptable to be used by people because of, ethical / cultural / religious, reasons AW