WA1 (Teacher) 2022 H1 Bio

Civics Group Index Number Name (use BLOCK LETTERS) ST ANDREW’S JUNIOR COLLEGE 2022 JC2 Weighted Assessment 1 H1 BIOLOGY 8876 STRUCTURED QUESTIONS 45 minutes READ THESE INSTRUCTIONS FIRST Write your name, civics group and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagram, graph or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. All working for numerical answers must be shown. Conceptual error (C) Data Quoting (D) Expression (E) Misreading the question (Q) For Examiner’s Use STQ 1 /14 STQ 2 /12 Total /26 This document consists of 6 printed pages. [Turn over H1

QUESTION 1 BRCA 1 and BRCA2 are tumour suppressor genes which code for tumour suppressor proteins associated with DNA repair. Women with harmful mutations in either BRCA1 or BRCA2 are five times more likely to develop breast cancer and 10 - 30 times more likely to develop ovarian cancer than women without any BRCA mutations. Fig. 1.1 shows the progression of breast cancer. Fig. 1.1 (a) (i) Describe and explain how the multi-step process of cancer development relates to the information given as well as Fig 1.1. ……………………………………………………………………………………………… [6] 1 Accumulation of many mutations, including BRCA 1 and BRCA2 2 lead to excessive proliferation of the duct epithelial cells 3 Activation of telomerase gene enables cells to divide indefinitely. 4 Further mutations can lead to loss of contact inhibition /density-dependent inhibition which leads to tissue invasion. 5 Ref. Formation of benign tumour. 6 Loss of anchorage-dependent inhibition leads to metastasis/motility. 7 At this point, the tumour is considered malignant. (ii) Compare between cancerous breast duct epithelial cells and normal epithelial stem cells. ……………………………………………………………………………………………… [4] Similarities: 1 Both are unspecialised and undifferentiated. 2 Both can replicate indefinitely / both have telomerase activity.

Differences [any 2]: Cancerous epithelial cell Stem epithelial cell Ability to differentiate Do not differentiate into other cell types. Differentiate into duct epithelial cells. Cell division Undergo uncontrolled cell division. Undergo normal cell division. Anchorage- dependent inhibition Do not exhibit anchorage - dependent inhibition. /density-dependent /contact-dependent Exhibit anchorag e-dependent inhibition. /density-dependent /contact-dependent (b) Fig. 1.2 shows the various types of cells that are found in the human skin. Cells in the spinous layer, granular layer and stratum corneum provides a barrier protection against pathogens in the external environment. Stem cells in the basal layer will divide and differentiate into committed progenitors, which can only divide a limited number of times to give rise to cells in the layers above it. Only 2 -7% of the cells in the basal layer are stem cells. Fig. 1.2 (i) Describe the differences between the skin stem cell and the committed progenitor cell. ……………………………………………………………………………………………… [2] 1 Skin stem cells are capable of self renewal / has telomerase while committed progenitors cells do not have/lower self-renewal ability / no telomerase. 2 Skin stem cells have higher potency level than committed progenitor cells. (note: both may be multipotent. But committed progenitor cells are more limited in the types of cells they can differentiate into) Human induced pluripotent stem cells ( hiPSCs) have been recognized as a possible source of cells for skin tissue engineering. They have the potential to greatly benefit patients with large areas of burned skin or s kin defects. Fig. 1.3 shows an outline of the production if hiPSCs and its use in treating burn victims.

Fig. 1.3 (ii) Suggest two advantages of using hiPSCs over the use of other types of treatment for burn victims. ……………………………………………………………………………………………… [2] 1 No tissue rejection because the patient’s own cells are used to produce the iPSCs, compared with using a donor’s stem cells. 2 Fewer ethical concerns because no human blastocysts were destroyed in the process, compared with the use of human embryonic stem cells. 3 Non-invasive as you just need to pluck a hair from the patient, compared to grafting skin from another part of the patient’s body. 4 No need to find a matching donor. [Total: 14] QUESTION 2 In a species of pea plants, the plants can produce smooth seed pods or constricted seed pods with seeds ranging from two to four seeds each. Fig. 2.1 shows the appearance of some seed pods that can be observed. Fig. 2.1 A pure -breeding plant with 4 -seeded constricted pods was crossed with a pure - breeding plant with 2 -seeded smooth pods. All the F 1 generation had 3 -seeded constricted pods. The F1 generation were selfed to produce F2 generation. (a) Draw a genetic diagram to show the selfing of the F1 generation. ……………………………………………………………………………………………….. [4] F1 phenotype: 3-seeded constricted pods X 3-seeded constricted pods

F1 genotype: CcSFSf CcSFSf F1 gametes: CSF CSf cSF cSf CSF CSf cSF cSf CSF CSf cSF cSf CSF CCSFSF 4-seeded constricted pod CCSFSf 3-seeded constricted pod CcSFSF 4-seeded constricted pod CcSFSf 3-seeded constricted pod CSf CCSFSs 3-seeded constricted pod CCSfSf 2-seeded constricted pod CcSFSf 3-seeded constricted pod CcSfSf 2-seeded constricted pod cSF CcSFSF 4-seeded constricted pod CcSFSf 3-seeded constricted pod ccSFSF 4-seeded smooth pod ccSFSf 3-seeded smooth pod cSf CcSFSf 3-seeded constricted pod CcSfSf 2-seeded constricted pod ccSFSf 3-seeded smooth pod ccSfSf 2-seeded smooth pod F2 phenotypic ratio: 3 4-seeded constricted pod : 6 3-seeded constricted pod : 3 2-seeded constricted pod : 1 4-seeded smooth pod : 2 3-seeded smooth pod : 1 2-seeded smooth pod. Mark scheme: 1 F1 phenotype match with genotype (use of superscript) 2 Gametes (circled) 3 Punnet square/F2 genotypes 4 F2 genotypes matched with phenotypes + F2 phenotypic ratio (b) An F2 generation plant with 3-seeded constricted pod was selected at random to be test crossed. Considering all possible scenarios, w hat is the probability of producing plants with 3 -seeded constricted pods? Show your working using genetic diagrams. ……………………………………………………………………………………………….. [6] Test crossing CCSFSf: F2 phenotype: 3-seeded constricted pods X 2-seeded smooth pods F2 genotype: CCSFSf ccSfSf F2 gametes: CSF CSf cSf F3 genotypes: CcSFSf CcSfSf F3 phenotypic ratio: 1 3-seeded constricted pod : 1 2-seeded constricted pod Probability of producing 3-seeded constricted pod = ½ Test crossing CcSFSf:

F2 phenotype: 3-seeded constricted pods X 2-seeded smooth pods F2 genotype: CcSFSf ccSfSf F2 gametes: CSF CSf cSF cSf cSf F3 genotypes: CSF CSf cSF cSf cSf CcSFSf 3-seeded constricted pod CcSfSf 2-seeded constricted pod ccSFSf 3-seeded smooth pod ccSfSf 2-seeded smooth pod F3 phenotypic ratio: 1 3-seeded constricted pod : 1 2-seeded constricted pod : 1 3-seeded smooth pod : 1 2-seeded smooth pod Probability of producing 3-seeded constricted pod = ¼ Mark scheme 1 F2 gametes (circled) (for 1st scenario) 2 F3 genotypes matched with phenotypes (for 1st scenario) 3 F3 phenotypic ratio (for 1st scenario) 4 F2 gametes (circled) (for 2nd scenario) 5 F3 genotypes matched with phenotypes (for 2nd scenario) 6 F3 phenotypic ratio (for 2nd scenario) [Max 5 marks for genetic crosses] 7 Over