IB DP Biology 1.6 Cell division Question Bank HL Paper 2

Question     

    (a) (i) Identify the stage of mitosis labelled X in the image, giving a reason. [1]

 

(ii) Outline what is indicated by the mitotic index of tissue taken from a tumour. [2]

(iii) DNA has regions that do not code for proteins. State two functions of these regions. [2]

1.

2.

(b) DNA methylation has a critical role in gene regulation by affecting transcription. Samples were taken from two colon cancer tumours (T1 and T2) and two normal colon samples (N1 and N2). A particular gene was implicated as a possible cause of cancer. The promoter of this gene was cloned (A–J). The data show the DNA methylation patterns from these samples. The numbers (32–269) represent different markers in the promoter.

        1. Outline the difference in methylation pattern between tumorous and normal tissue samples. [2]

        2. Suggest a way methylation may affect tumour cell genes. [1]

▶️Answer/Explanation

Ans:

a i

         telophase because the chromosomes/chromatids have reached the poles
OR
«late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔

a ii

         a. mitotic index is an indication of the ratio/percentage of cells undergoing mitosis/cell division ✔
b. cancer cells «generally» divide much more than normal «somatic» cells ✔
c. a high/elevated mitotic index in tumours / possible diagnosis of cancer /measure of how aggressive/fast growing the tumour is ✔

a iii

a. promoters / operators / regulation of gene expression/transcription 

b. telomeres/give protection to the end of chromosomes «during cell division» 

c. genes for tRNA/rRNA production 

d. other valid function for non-coding sequence

b i

a. «overall» much more methylation in the colon tumour samples than normal 

b. tumour and normal samples the markers 258 and 269 similar degree of methylation/fewer differences 

c. degree of methylation on certain markers may correlate with the presence of cancer / correct example of a marker only methylated in tumour cells eg marker 32 

b ii a. «DNA» methylation may inhibit transcription of genes that would prevent cancer/tumor formation

Question

Multicellular organisms benefit from cell specialization and division of labour.

(a) Outline the processes occurring during interphase in the cell cycle.[4]

(b) Describe what occurs in a neuron when an action potential is propagated along the axon. [4]

(c) Explain how cells in the bloodstream cause a specific immune response.[7]

▶️Answer/Explanation

a a. growth/increase in cell size;

b. division of mitochondria/chloroplasts/production of more organelles/number of organelles doubled;
c. replication of DNA/amount of DNA is doubled;
d. transcription of genes/production of mRNA;
e. protein synthesis;
f. cell respiration/production of ATP;

b a. sodium ions/Na+ enter/diffuse in;

b. depolarization/membrane potential/voltage changes from negative to positive;
c. potassium channels open AND potassium ions/K+ exit/diffuse out;
d. repolarization/membrane potential/voltage changes back from positive to negative;
e. local current due to diffusion of sodium ions along the neuron;
f. (local currents) cause next sodium channels to open/next part of axon to depolarize;
g. opening of sodium channels triggered when threshold potential/-50mV reached;

c a. (specific immune response is) production of antibodies in response to a particular pathogen;
b. antibody is specific to/binds to a specific antigen;
c. macrophages/phagocytes engulf/present antigens from pathogens/viruses/bacteria;
d. T lymphocytes activated by antigens/antigen presentation/antigens presented by macrophage;
e. (activated) T lymphocytes activate B lymphocytes;
f. only B lymphocytes that produce antibodies against the antigen/pathogen are activated;
g. (activated) B lymphocytes clone/divide by mitosis to form plasma cells;
h. plasma cells then secrete (large quantity) of an antibody/secrete antibodies of same type;
i. some B lymphocytes/plasma cells form memory cells;
j. memory cells give long lasting immunity/faster response to a disease/pathogen;

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