CHIJ St Nicholas 2016 Bio Prelim P2 MS

7 Paper 2 Section A (80 marks) Qn Answer Marks Markers’ Report 1(a) Long and narrow protrusion/extension; To increase surface area to volume ratio for absorption/diffusion; [1] 0.5m each Function is not for exchange of substances 1(b) 51/1.6= x31.9 [1] Many candidates do not know that 1cm = 10mm 1(c) Structure 1 Structure 2 glucose Diffusion and active transport NA Amino acids Diffusion and active transport NA Fatty acids NA diffusion [2] Any mistakes minus 0.5m 2(ai) 0.6:1 [1] 2(aii) As SA:VOL ratio decreases rate of diffusion decreases (or vice versa); Use figures with correct units (mms-1 for rate) to illustrate trend; The larger the plant, the lower the SA:V ratio; Plants cannot rely on diffusion to absorb nutrients (will require to carry out active transport) [2] 0.5m each 2(b) First student’s answer; The student considered the SA:V ratio than the length of the cube only. [2] 1m each Also accepted: The first student divided the answer by 2 as distance has to be to centre of cube rather than whole length of side/ Student assumed diffusion occurs (across whole cube) from whole length of one side; 171 trendylinedered the SA:V ratio than the length of t achT istance has to be whole length of side/ Studeassumeddiffu whole cube) fromwhotrendyyyyline

8 Qn Answer Marks Markers’ Report 3(a) Blurred vision/delayed speed of reaction/increased reaction time/impaired judgement/slower reflex actions [1] Any one 3(b) 184mg per 100cm3 [1] 3(c) Alcohol dehydrogenase produced by the liver; Will catalyse; the breakdown of alcohol into acetaldehyde; then further into compounds used for respiration [2] 0.5m each 3(d) Extend line using ruler until it reaches the dotted line; Read off time on dotted line [1] 0.5m each Ideal answer: 9.12am Each small box is 24 minutes 4(a) Double circulation means blood passes through the heart twice in one circulation; Pulmonary circulation and systemic circulation; blood flows out through pulmonary artery to capillaries in lungs; blood flows out through aorta to arteries to body and returns to heart through veins; [2] 0.5m each In description, reference must be made to Figure 4.1 – at least 1 part of circulatory system from the figure must be explicitly named Need to mention that blood from capillaries flows back to the heart 4(b) Oxygen molecules combine with haemoglobin in red blood cells; To form oxyhaemoglobin; When muscles in wall of left ventricle; contract / undergo ventricular systole; The pressure in the left ventricle increases; and becomes higher than aorta; aortic valve opens; (semilunar valve – 0m) blood flows through hepatic artery to liver; oxygen in blood diffuses; from red blood cell into plasma into tissue fluid and into liver cells; [Max 4] 0.5m each Description should only start from point at which oxygen is forced out of left ventricle of the heart, and not from left atrium / lungs. 172 trendylineer t;(semilunar valv tgh hepatic arteryto liver; treffus; trl inplasma into tissue fluid and into liv yyyy

9 Qn Answer Marks Markers’ Report 4(ci) tissue fluid blood only phagocytes present presence of blood cells e.g. RBC and WBC (lymphocytes) absence of plasma proteins presence of plasma proteins [2] 1m each complete point to point comparison: 1m *Note: tissue fluid is not plasma; plasma relates to the liquid component of blood, while tissue fluid refers to that outside the blood vessels and surrounding tissue cells. 4(cii) Higher pressure at arterial end; forces blood plasma out through capillary wall; [1] 0.5m each 5(a) A: trachea/windpipe B: diaphragm [1] 0.5m each wrong spelling 0m 5(bi) partition walls between alveoli (C) will break down; decreased surface area for gaseous exchange; lungs lose elasticity and becomes inflated with air; person will suffer from wheezing and breathlessness/ have difficulty breathing [2] 0.5m each 5(bii) - more than 3 breaths taken; - each breath is shallower [1] Since lungs are inflated with air, the starting volume of air in the lungs should be higher than normal. 5(c) Tar/Irritants; paralyse cilia found on D (epithelium); dust particles trapped in the mucus cannot be removed; block airways [2] 0.5m each D is not the cilia. 6(ai) Fluid P: glomerular filtrate Fluid Q: urine [1] 0.5m each Many candidates fail to understand requirement of question and name the part of nephron or sweat. 173 trendylinear filtrate tr [1 0.5m each Many candidates fail of question and name swea td litrendyyyyline

10 Qn Answer Marks Markers’ Report 6(aii) glucose present in fluid P because it is a small; molecule; will be forced out during ultrafiltration; no glucose in fluid Q because they have been selectively reabsorbed; [2] 0.5m each Many candidates gave long-winded answers about the other components in the filtrate while missing out on GLUCOSE. 6(bi) to prevent blood from clotting/coagulating Any reference to agglutination/ RBC clumping – 0m [1] Agglutination occurs in presence of antibodies; not applicable in this situation 6(biii) dialysate does not contain any metabolic waste products; dialysate flow is opposite direction of blood flow; to generate a steep concentration gradient; ensure faster diffusion of waste products; tubing is long and coiled; increase SA:V ratio for the fast diffusion of waste products; tubing is partially-permeable; to retain large molecules, only allowing small waste products to diffuse out [2] 0.5m each Function of dialysis is to remove urea from the blood, not to replenish lost mineral salts, hence focus should not be on salt concentration. If partially-permeable property mentioned then focus should be on the fact that it retains large molecules and allows only small molecules to diffuse out 7(ai) Cross pollination; because from different plant/ different plot of land [1] Some candidates were careless and stated wind/insect pollination, which is the MODE of pollination. 7(aii) offspring produced may have inherited beneficial qualities from both parents [1] more varieties of offspring can be produced/more genetic variation; hence greater chance of survival in the event of changes in environment/ better adapted in changing environment; [2] 0.5m each 174 trendylineoffspring can be produced/more genetic nce of survival in the event of changes er adapted in changing environment; h trendyyyyline

11 Qn Answer Marks Markers’ Report 7(bi) Selective breeding/pollinate/cross breed/hybridise; Select teosinte plants with softer and more kernels/larger fruits; Select plants with more and softer kernels and larger fruits; Repeat breeding and selection process many times to cross pollinate to produce maize; [2] 0.5m each Many candidates still unsure how to carry out selective breeding; teosinte is the ANCESTOR of maize, it is impossible to cross-breed maize with teosinte. Also there is no genetic engineering involved. 7(bii) difference in sequence of 5th codon ( AAG Æ AAC); different mRNA sequence produced/state mRNA sequence; which will code for a different polypeptide/ different amino acid added; and hence different function of protein [2] 0.5m each Many candidates still make the mistake of saying that amino acids are made in the cell instead of being added to the growing polypeptide. Also they failed to link the structure of protein produced to their function. 8(a) Having 2 sets of chromosomes; each set inherited from one parent; [1] 0.5m each 8(b) - 4 chromosomes - colour one set of chromosomes to denote paternal/maternal - chromosome made up of 2 sister chromatids - spindle fibre attached to centromere -d a u g h t e r c h r o m o s o m e s m o v i n g t o o p p o s i t e p o l e s (anaphase) - show at least one event of crossing over [2] any mistakes -0.5m 175 trendyline

12 Qn Answer Marks Markers