2018_Cell-Nuclear-Division_STQ_QP

2018 Cell and Nuclear Division STQ 2018 / H2 / ACJC PRELIM / P2 Q6 (Mutations)1 Many diseases arise due to gene mutations and/or chromosomal aberrations.(a)Distinguish between gene mutations and chromosomal aberrations.[2]Fig. 6.1 shows an error occurring during meiosis II. Fig. 6.1(b)(i)Complete Fig. 6.1 with the correct chromosome structures and chromosome number (in terms of n) in the gametes. [2] Meiosis IMeiosis IIGametesChromosome number (in terms of n) Chromosome number=2n

(ii)Explain the error shown in Fig. 6.1.[2](iii)Predict the chromosomal number (in terms of n) in each of the four gametes if a similar error had occurred in meiosis I instead of meiosis II.[1](c)Such errors can occur during mitosis too. Comment on whether this would lead to changes in the gene pool of a population.[1] [Total: 8]

2018 / H2 / EJC PRELIM / P2 Q3 (Stem Cells)2Bone marrow contains stem cells that divide by mitosis to form blood cells. The fate of a stem cell was tracked and it was recorded that during the observed duration the stem cell divided asymmetrically each time. Fig. 3.1 shows changes in the mass of DNA in a human stem cell from bone marrow during three cell cycles. Fig. 3.1(a)With reference to the information provided above, (i)Describe what happens to bring about the changes in the mass of DNA per cell at time period K and at time period L. K …………………………………………………………………………………………………… ……………………………………………………………………………………………………… L …………………………………………………………………………………………………… …………………………………………………………………………………………………...[2](ii)State one function of these stem cells undergoing the above type of cell division. ……………………………………………………………………………………………………… …………………………………………………………………………………………………...[1](iii)The process of meiosis is significant to natural selection in evolution.Explain this significance. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………...[2]A bone marrow cell was extracted and observed under the electron micrograph shown in Fig.

3.2. The student focused on an organelle which he described as having “an envelope surrounding genetic material containing both darker and lighter stained patches, distinct from the site where ribosomal subunits were assembled”. Fig. 3.2(b)Explain the significance of the “darker and lighter stained patches” that the student referred to, in a cell undergoing differentiation.………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………