2017 HCI H2 Biology Prelims Paper 2 Answers

1 HWA CHONG INSTITUTION / 2016-2017 H2 BIOLOGY / Preliminary Examinations / Paper 2 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2017 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 2 MARK SCHEME STRUCTURED QUESTIONS Question 1 (a)(i) Outline the cell theory. [max 2] any two: 1. living organisms composed of cells 2. cells form most basic unit of life 3. cells arise from other cells (a)(ii) With reference to Figure 1.1, explain how Pasteur’s experiment supports the cell theory. [2] 1. description of what happens to the nutrient broth (ref to stimulus) 2. shows that cells must come from pre-existing cells (a)(iii) Suggest a reason for the universal acceptance of the cell theory in our world today. [1] any one: 1. tested / scrutinized by other scientists 2. reproducible 3. overwhelmingly supported by scientific community (b)(i) State the name and chemical composition of the stuctures labelled A to C. [3] name chemical composition A 1a. cell wall 1b. peptidoglycan B 2a. cell membrane 2b. phospholipids and proteins C 3a. nucleoid 3b. DNA

2 HWA CHONG INSTITUTION / 2016-2017 H2 BIOLOGY / Preliminary Examinations / Paper 2 / MS 2 (c) P. syringae can cause disease in the leaves of its host plant by secreting toxins and cell wall degrading enzymes, without causing harm to itself. Explain why this is so. [2] 1. ref to toxins affect the functioning of membranous organelles 2. ref to different composition of cell wall 3. ref to specific 3D conformation of enzymes (d) State and explain which of the three types of interactions best describes the relationship involved in the endosymbiotic theory. [2] 1. mutualism 2. prokaryote produces ATP, host cell provides shelter / nutrients [Total: 12] Question 2 (a) With reference to Fig. 3.1, (i) name the stage of mitosis shown. [1] (late) anaphase (ii) describe what is happening during this stage of mitosis. [2] 1. centromere divide, forming daughter chromosomes 2. migrate to poles, centromere leading 3. pulled by kinetochore microtubules (b) Distinguish between multipotent cells and totipotent cells. [max 2] 1. multipotent more specialized 2. multipotent cells cannot give rise to organs but totipotent cells can 3. correct example of multipotent cell and totipotent cell (c) Suggest why there might be a connection between the use of stem cells in treatment and c a n c e r . [ m a x 3 ] 1. stem cells may undergo uncontrolled cell division 2. telomerase active 3. risk of developing tumour where stem cells implanted 4. ref to exposure to carcinogens 5. appropriate ref in context to cancer critical genes (d) State whether you agree or disag