West Spring 2018 Bio Prelim P2 MS

1 SECONDARY 4 EXPRESS BIOLOGY PRELIMINARY EXAMINATION, 2018 SUGGESTED MARK SCHEME P2 Section A Answers Marks Remarks 1( a ) [1] (b) 1. Leaves that contain insecticides are eaten by the caterpillars. As these insecticides are not biodegrable/are not broken down, they accumulate in the bodies of caterpillars./ bioaccumulation ; 2. As birds feed on the caterpillars and hawks feed on these birds, the concentration of insecticides increases along the food chain. ; 3. Highest concentration of insecticides will be found in hawks. ; 4. This is known as bioamplication/bioaccumulation ; Reject: indigestible [1] [1] [1] [1] Point 1 is a must Point 2, 3 and 4, any 2 Max 3 marks (c) (i) 1. Initially, the grasshopper population increases as there are less predators feeding on them and they can reproduce more. ; 2. However, their population decreases later dramatically due to the competition for food. ; 3. The flowering plant is the only producer of food in this food web/does not produce enough food for the growing population. ; [1] [1] [1] (c) (ii) 1. Initially, the caterpillar population remains constant because they belong to two different food chains / snakes do not prey on them./have not lost source of food or predator ; 2. However, both grasshoppers and caterpillars feed on the same food source (leaves of flowering plant), an increase in the population of grasshopper provides competition for food with the caterpillars. ; Or No snakes, grasshopper population increases, more food for birds, bird population increases, more caterpillars are eaten [1] [1] www.KiasuExamPaper.com b) 1. Leaves that contain insecticides are eaten by the caterpillars. As these insecticides are not bioddegegegegegegegegegegegegegegegeggggeggegggegggggggegggggegggeggggggeggeggggggegegeggggggeggeggggggggeggggeeegggggggggggggegegggggggggggggggggrarararararrarararaarararararararararararrararararrarrarararrrrrararrrarrarararararrrrarararaarrrrraararaaararrrraarrrarrrarararrrarraaaarrraaaaararaaaaaraaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaraarraaaaablblblblblbbblbbbbbbblblbbblblblbblblblblblblbbblbblblbblbbbbbbblblbbblbbbbbbbbbbbbbbbbbbbbbbbblbbblbbblbbbblbbbbbbbbbbbbbblbbbbbbblbblbblllllblblblbblblllbllllbllbblbblblbbbblbbbbbbbbbbbbbbbbbbbe/e/e/e/e/e/e/e/e/e/e/eee/e/e/e/e/e/e/e/eee/e/e/e/ee/e/e/e/e/e/e/ee/e/e/e/ee/eee/e/e/eee/ee/ee/e/e/e/e/e/e/e/e/ee/e/e/e/ee/ee/e//e/ee/e/e/eee///e/e/e//eee//e///e/e//e/e/////////e///e//e///e/e/e//e////e/eeee/eeeeeeee////araraararaararaaaararararaararararararararaaaararaarararararararrararararaaaarararrararaaaaaaaaaararrarararararaaaaaaarrrararararararararaaaaarararrrrraararrraararaaraaaaaraarraaaaaaaaaraararaaraaraaaaaaraaarrraaaaraaaaeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee not broken down , they accumulate in the bodododododddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddieieieeeeeieeieieieeieieieeieeieieieeieieeieieeeieeeieeieeeieieeeieieeeeeeiieieieiiiiieieiiiieieeieieieeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees ssssssssssssssssssssssssssssssssssssssss sss sssssssss ssssss sssssssssssssssssssssssssofofofofofofofofofofofofofoofofofofofofofooofofofofofofofoofofofofofofofofofoofofofofofofoofofofooofofofofofofofoooofofofofofoooofoooooooooofofoofoofooooffooooofoofoofooooofoofofoofoofofoffofffffffffffffffofffoooofffoofoofoofoofo caterpillars. / bioaccumulation ; 2. As birds feed on the caterpillars and hawks feed on these birds, the concentration of insecticides increasses along the food chain. ; 3. Highest concentration of insecticides will be founundd in hawks . ; 4. Thisisknownas bioa mplicatitionon /b/biooaaccuumumulalatitionon ; R eject: indigestible [1]] [ 1] [ 1] [ 1] Point 1 is mumst Po int 2 , 3 and 4, any M ax 3 ma c) i) 1.1 Initially, the grrassshhopoper popopupulalatio n increases as there are less predataors fefeededinggonontthehemmanad they can reproduce more. ; 2. However, theirppopopululatatioionndecreases later dramatically due to the cocompmpetetititioion fofor r fofood . ; 3. The flowowererininggplpanant tis the only producer of food in this f ood web/ doeses nototpprorduce enough food for the growing populationn.. ;; [1] [ 1] [ 1] c) 1. Initially, the caterpillar population remains constant because [1] 499

2 2( a ) The healthy child has more villi /more protrusion patient has fewer villi / The healthy child’s villi are longer / patient has shorter villi / Patient’s villi are not properly formed/ Healthy child has villi separated/ Healthy child has larger surface area for villi; [1] Any 1 point Reject: Villi has more folds, (b) 1. Microvilli provide a larger surface area to volume ratio for food to be absorbed faster. ; 2. Each villus is supplied with a network of blood capillaries to maintain a steep diffusion gradient for rapid diffusion of food substances. ; 3. The villi are thin walled / one cell thick walls of villi provide a short diffusion distance for digested food to pass through the walls quickly. ; 4. The small intestine is long to allow more time for digested food to be absorbed ; 5. Mitochondria are found in the cells of the epithelium to help in the absorption via active transport. [1] [1] [1] [1] [1] Any 3 points (c) 1. Enzymes are specific in action / Each protein must be digested by one specific enzyme. ; 2. Each enzyme has an active site. 3. The shape of the active site is complementary to shape of substrate / only allows a particular substrate to fit in to form an(enzyme-substrate complex) not necessary ; 4. Hence, the enzyme which digests protein in the meat cannot digest protein in gluten. ; [1] [1] [1] No mark 3( a )1. Anthers, outside flower / exposed, to allow wind to carry pollen away / 2. Long / flexible filaments/pendulous stamens, to allow wind to dislodge the pollens / 3. No / small petals, to allow anthers to be exposed to the wind / less energy is channelled to produce large petals and more energy channelled to make pollens instead 4. Anthers large to produce large quantities of pollen [1] [1] Any 2 points (b) 1. (Genetic) mutation occurs in the corn borer ; (there are variation in some corn borers) 2. Mutated Corn borers more likely to survive / have selective advantage ; 3. These corn borers grow into adults and are likely to breed / reproduce ; 4. Hence, the mutated gene / resistance alleles are passed on to the next generation ; 5. This leads to increase in frequency of allele for resistance ; [1] [1] [1] Any 3 points (c) rr [1] (d) 1. When non-resistant borers from outside breed with resistant borers, many offspring will not be resistant ; 2. Because many of the offspring will be Rr / heterozygous/less will be rr ; 3. Detail e.g. results of rr / RR andrr x Rr [1] [1] Max 2 points www.KiasuExamPaper.com ; 3. The villi are thin walled / one cell thick walls of villi provide a short diffusion distance for digested food to pass through the walls quickly . ; 4. The small intestine is long to allow more time for digested food to be absorbed ; 5. Mitochondria are found in the cells of the epithelium totototototohhhhhhelelelelelelpppppp in the absorption via active transport. [ 1] [[[[[[ 1]1]1]1]1]1] [ 1] c) 1. Enzymes are specific in action / Each protein mmmmumumumumumumumuumumumumumumumumumuuumumumuuuumumumumuuuumumuuumumumuuumuumuuuuumumuuuuuumumuuuuumuumumuumuuuuuummuuummmumuumumuumumummmmuuummmmmuuuststststsstststsststststststssststststststssttstssttststsstststssstststststststststststtttttttsttststtttsttttsstttstststststttstststttstststttstststtttstsssssttststsstssssstssssstsststssssssssstsssssssstsstttssssstttsbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee digested by one specific enzyme. ; 2. Each enzyme has an active site. 3. The shape of the active site is complementary yto shape offffff substrate / only allows a pa