A-LevelBiologyCell structure9700/21 · Oct/Nov 2018 · Q411 Marks

Fig. 4.1 is a photomicrograph of a cross-section of a tubular structure in the kidney made from epithelial cells. [Figure 4.1]

(a)The actual length of epithelial cell A along the line P-Q is 35 µm. Calculate the magnification of the image shown in Fig. 4.1. Write down the formula and use it to make your calculation. Show your working. formula magnification ×[2]
(b)(i)Some epithelial cells in the kidney release the protein vascular endothelial growth factor (VEGF). This protein is a cell signalling molecule that stimulates cell division in endothelial cells in blood vessels. State what occurs during interphase to prepare a cell for division.[2]
(b)(ii)Explain how a cell signalling molecule, such as VEGF, can lead to a response in a cell.[2]
(c)Uncontrolled cell division may result in a tumour. Tumour cells in the kidney respond to VEGF. Kidney cancer can be treated with monoclonal antibodies. These monoclonal antibodies bind to VEGF. Outline the hybridoma method for the production of monoclonal antibodies that will target the VEGF protein.[4]
(d)Monoclonal antibodies used as a treatment need to be given more than once. Repeated treatment can cause side effects to the person or can become less effective. Suggest why repeated treatment with monoclonal antibodies may have these effects.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[2] (a) correct formula ;
[2] (a) (×) 1200;
[2] (a) A 1171 (41 000÷35)
[2] (a) 1229 or 1228.6 (43 000÷35)
[2] (a) max 1 if units given
[2] (b)(i) any two from DNA, replication / AW ; A S phase I chromosome replication
[2] (b)(i) (early interphase) chromosome becomes two chromatids ; A described
[2] (b)(i) DNA checked for errors / errors in DNA repaired;
[2] (b)(i) synthesis of, (growth) protein / enzymes (for growth) ;
[2] (b)(i) cell growth;
[2] (b)(i) organelle synthesis ;
[2] (b)(i) centrioles replicate;
[2] (b)(i) AVP; e.g. ref. to checkpoint(s)
[2] (b)(i) nucleotide synthesis
[2] (b)(ii) any two from ref. target cells are endothelial cells ;
[2] (b)(ii) VEGF / cell signalling molecule, binds / AW, to receptor; R receptor cells
[2] (b)(ii) ref. specificity (of receptors) / VEGF / cell signalling molecule, complementary to receptors ;
[2] (b)(ii) suggestion of detail following binding ; e.g. triggers secondary messenger
[2] (b)(ii) activates enzymes / enzyme cascade
[2] (b)(ii) signal transduction
[2] (b)(ii) phosphorylation events
[4] (c) any four from VEGF protein / antigen, injected into, mouse / small mammal;
[4] (c) time for immune response to occur; A description of event in immune response
[4] (c) plasma cells / B-lymphocytes / splenocytes, extracted from mouse ;
[4] (c) plasma cells / AW, fused with, myeloma / cancer, cells;
[4] (c) (to produce) hybridoma cells ;
[4] (c) clone hydridoma cells ;
[4] (c) separate cells and culture in individual wells ;
[4] (c) screen for cells secreting desired antibody ;
[4] (c) hybridoma cells grown in large scale culture / AW ;
[4] (c) AVP; e.g. ref. to fusogen
[1] (d) any one from monoclonal antibodies identified, as foreign / non-self / act as an antigen ;
[1] (d) (monoclonal antibodies) stimulate an, immune / allergic, response ;
[1] (d) AVP; e.g. (antibodies destroyed so) not enough antibody (to be effective)