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.…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...[3] The use of embryonic stem cells (ESCs) for stem cell therapy and research is controversial and considered by many people as unethical. Scientists have circumvented this issue through the use of induced pluripotent stem cells (iPSCs) as an alternative to ESCs. Fig. 3.3 summarises the procedure for obtaining iPSCs and its use.

Skin fibroblastsAddition of reprogramming genesInduced pluripotent stem cells Heart cellsFat cellsBlood cellsBrain cellsDifferentiationFig. 3.3 (c)Explain why the use of iPSCs is preferred over ESCs.…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...[2][Total: 10]

2018 / H2 / JJC PRELIM / P2 Q73Fig. 7.1 shows an electron micrograph of a chromosome in prophase II. Fig. 7.1(a)Name the structures A and B. [2]A _________________________________________________________________B _________________________________________________________________(b)Explain why the chromosome occurs as a double structure. [2]____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ BA

The risk of mis-segregation of chromosomes increases with age among women. This can lead to aneuploid embryos. Fig. 7.2 shows an oocyte undergoing nuclear division with mis-segregated and lagging chromosomes. Fig. 7.2(a)Identify the stage in meiosis as shown in Fig. 7.2. [1]___________________________________________________________________(b)With reference to Fig. 7.2, suggest how aneuploid embryos are formed. [3]__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[Total: 8]

2018 / H2 / NYJC PRELIM / P2 Q2Fig. 2.1 shows some Allium sp. plant cells in various stages of the mitotic cell cycle. Fig. 2.1(a)(i) Identify the three stages shown by the labelled cells.ABC [3](ii)Identify the stage of mitosis that follows that shown in cell C. [1](iii)In the cell outline below, draw and label the structures visible in a cell that is in the stage you have named in (ii). 2n for this plant is 6. [3] cell wallcell surface membrane

(b)Uncontrolled cell division can result in cancer. Some types of cancer can be treated by chemotherapy, which involves the injection of chemicals into the bloodstream.One chemical used for chemotherapy is called Methotrexate. This is a reversible competitive inhibitors of one of the enzymes in the metabolic pathway that results in the formation of purines.Explain how the use of Methotrexate will slow down the mitotic cell cycle. [2](c)Prokaryotic organisms such as Escherichia coli divide by simple cell splitting (binary fission), not mitosis.Apart from ribosomes, prokaryotes have no organelles comparable to those found in eukaryotes and have a circular ‘chromosome’ with no centromere. With reference to the information above and your knowledge of mitosis, suggest why mitosis does not occur in prokaryotes. [2][Total: 11]

2018 / H2 / PJC PRELIM / P2 Q45There have been many breakthroughs in stem cell research in the recent years. It has been discovered that stem cells are involved in the replacement of worn-out cells and repair of damaged tissues. Further research is being conducted to better understand the mechanism involved in controlling the behaviour of stem cells in order to better manipulate them to treat various diseases and disorders.Stem cells undergo cell division to produce genetically identical daughter cells. Fig. 4.1 shows two cells, each at a different stage of cell division. Fig. 4.1(a)With reference to Fig. 4.1, state the stages of cell division in Cell A and Cell B. Cell A ………………………………………………………………….Cell B ……………………………………………………………… [1] Cell A Cell B