2008 Biology Paper I Marking Scheme

8/4/2019 2008 Biology Paper I Marking Scheme

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2008 Biology

Marking Scheme

The marking scheme was prepared for markers' reference. It should not be regarded as a set of model answers.Candidates and teachers who were not involved in the marking process are advised to interpret its contents with care.The examination emphasises the testing of understanding, the practical application of knowledge and the use ofprocessing skills. Students are advised to study this document in conjunction with the examiner's comments oncandidates' performance in this booklet.

Biology Paper 1

General Instructions1. For terms marked with '*', correct spelling is required.2. In questions asking for a specified number of reasons or examples etc. and a candidate gives more than that is

required, the extra answers should not be marked. For instance, in a question asking for two examples to begiven and a candidate gives three answers, only the first two should be marked.

Guidelines for Assessing Effective Communication

4 parts from Section A and 1 part from each question of Section B are chosen for assessing effective communication.A maximum of one mark can be awarded in each part. The mark scale below serves as a guide to markers for awardingmarks on effective communication.

Marks awarded Criteria on effective communication

Answers organised, clear, fluent and coherent. Ideas are accurately and conciselycommunicated to meet question requirements with no/little irrelevant material.Arguments/reasoning where required are logically, systematically and critically presented.Shows a good command oflanguage, and is easy to understand.

Answers organised but lacking clarity and fluency. Ideas presented meet questionrequirements but contain some inappropriate use of words. Arguments/reasoning whererequired are acceptable but weak. Language used is understandable but with repetitionsand irrelevant material which sometimes blurs the main ideas.

o Answers disorganised and confused. Markers have to spend a lot of time and effort tolocate key points. Language used is almost incomprehensible with irrelevant materialburying the ideas required by the questions.


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MarksSection A

J . (a) Structure A produces bile 1which is released into the duodenum 1to help the digestion of fat / to emulsify fat 1to rovide an alkaline medium for e es to work " ".... 1E ective Communication C 1

(b) (i) Protect inner surface oftbe stomach from self-digestion 1(ii) Provide optimum f suitable pH for enzyme activity I to kill bacteria J(iii) Break down proteins into peptides lamina acids 1(iv) Break down fat into glycerol and fatty acid I(v) Sodium hydrogencarbonate I

Total: 9 + 1 marks

2. (a) To harbour more neurones ..(b) Y: * medulla oblongata ..

It acts as the reflex centre for some reflex actions } .It controls involuntary actions anyone .(c) Motor area ..(d) Sensory area .

Total: 5 marks

3. (a) X: * pleural membrane ..It secretes pleural fluid " ..to reduce friction during breathing movement ..

(b) (atmosphere) ~ nasal cavity= pharynx - - - + trachea - - - + bronchus - - - + bronchiole - - - + (air sacs) 2(c) Volume of the inspired air decreases ..

Less fresh air mixes with the residual air, thus concentration of carbon dioxide in the air sacs remainsrelatively high ..

The concentration gradient of carbon dioxide between the alveolar air and the blood becomes smallerThe rate of removal of carbon dioxide from blood decreases .ORVolume of the expired air decreases, carbon dioxide removed from air sacs to atmosphere decreases, ]thus concentration of carbon dioxide inside the lungs remains relatively high '" 1The concentration gradient of carbon dioxide between the alveolar air and the blood becomes smaller 1The rate of removal of carbon dioxide from blood decreases 1

I Efftctive Communication (C) (1) ITotal: 9 + lmarks4. (a) * Prokaryotae* Protoctista

* Fungi} any two . 1,1

(b) C~ll membrane, cytoplasm 1,1(c) (i) Make cell structures more distinct ..

(ii) Cover the tissue with a cover slip ..Total: 6 marks

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Marks5. (a) Cell type A has a thicker cell wall .

There is no end wall for cell type A while there are end walls for cell type B .(b) It forms a hollow tube / has no cytoplasm I no end walls 1+

which offers less resistance to the transport of water 1( c) Roots have no chloroplasts for photosynthesis .. 1

Therefore, they rely on the transport of sugars / food I organic substances from the leaves Ifor respiration and groWth 1

t Effective Communication (C) (1) ITotal: 7 + lmarks

6. (a) Ginger juice contains an active ingredient / heat sensitive substance / enzyme that causes the curdingof milk

(b) The active substance I heat-sensitive substance / enzyme is protein in nature ..which is denatured by high temperature ..Therefore, if the protein is involved, the action will be lost after boiling ..ORThe active ingredient I heat sensitive substance is a volatile substance ..which is evaporated by high temperature 1Therefore, if a volatile substance is involved, the action will be lost after boiling 1

(c) Follow the steps in the recipe for one set-up .and heat the milk to 65C instead of steps 2 and 3 in another setup ..

Total: 6 marks

7. (a) There is greater muscle mass after the training ..Muscles are made up of active cells that require more energy .

(b) There is an increase in the daily energy expenditure due to increased basal metabolic rate I energyexpenditure also-increases during training .

Thus the energy expenditure is greater than the energy intake Iour bod has to utilize the stored fat to meet the ener demand "........ I

1

(c) The intake of protein should be increased 1+as it is the major raw material for building muscles ;............................... IThe intake of calcium I phosphorus should be increased 1+as it is the major rawmaterial for building bones ..................................................................................1

(d) The stroke volume increases after the training ..This increases the amount of oxygen and carbon dioxide transported per heartbeat .A low heartbeat rate is sufficient to sustain the same intensity of exercise I Exercise of higherintensity can be performed by the person :........................................ f

Total: 12 + 1marks

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Marks

Section B8. (a) Title (T) ..

Correct plotting and joining of points (P) ..Correct labelling of curves (G) .e.g.

Title: Effects of the use of fungicide on the yield of wheat when different amount of fertilizers were added

(i)

o 80 160 240 320Mass of inorganic fertilizers added (kg)

(ii) Any three of the following: 1;1,1The yield of wheat increases with the increase in the amount of fertilizer addedexcept in the absence of fungicide, the yield of wheat decreases when fertilizers added ishigher than 240 kgThe yield of wheat is higber in the presence of fungicide than in the absence of fungicideThe difference in the yield of wheat between the presence and the absence of fungicideincreases when the use of fertilizers increases

(iii) Leaching of fertilizers to the aquatic habitat nearby, e.g. rivers, .will lead to the rapid growth of algae / algal bloom ..Anyone of the following: 1Other organisms in the habitat will suffocate due to oxygen depletion at nightThe algae may block the gills of the fish and suffocate itThe algae may produce toxins which kills other aquatic organismsAbundant of suspended algae prevents light from reaching the aquatic plants below

Total: 9 marks

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Marks8. (b) (i) Diabetic patients lack insulin / do not have enough insulin in their blood ,.. 1an d hence the liver fails to convert glucose into glycogen for storage I

During intense exercise, blood glucose is consumed for muscle activities 1The blood lucose level dro s continuous I without re lenishment from the I co en stored .. 1

I(ii) (1) It takes time for starchy food to be digested before absorption ..

As a result, a small amount of glucose is absorbed gradually .The fluctuation of blood glucose level is less / blood glucose level will not increase toofast after a normal meal .

(2) Sugar is easily digested I absorbable .Blood glucose level can be raised immediately to alleviate the symptoms of

hypoglycaemia .. Total: 9 + I marks

9. (a) (i) Vegetative propagation(ii) The chromosomes from A fail to pair up with the chromosomes from B during meiotic cell

division ..because they are not homologous chromosomes ..Therefore, hybrid C fails to produce gametes

(iii) (1) Wind .Feathery stigmaStigma exposedAnthers exposed ] Absence of petals

} any two .. 1,1

(2) During the experiment, use a plastic bag to wrap the treated flowers except during thefollowing treatments ..Remove the anthers from the flowers .Use a brush to transfer the pollen grains from other flowers to the stigma of the treatedflowers II Effective Communication (C) (1)

Total: 9 + 1marks

9. (b) (i) (1) (Heart)-4B-4D-4E-4C-4A .(2) Blood flows from a high pressure region to a low pressure region ..

(ii) When the ventricle of the heart contracts, blood is forced into the artery B, resulting in theincrease of blood pressure .Blood in the artery flows forward along the blood vessels while the ventricle of the heartrelaxes, as a result the blood pressure drops ..

(iii) White blood cel1s (lymphocyte / phagocyte) .Antibodies ..(Accept other alternatives)

(iv) Vaccine injected reaches the tissue fluid ..which drains back to lymph vessels I capillary .and returns to the heart via a vein ..

Total: 9 marks

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Marks10. (a) (i) Muscle contraction generates a lot of heat during heavy exercise .When heat production is greater than heat loss, the body temperature increases .

(ii) The superficial blood vessels dilate 1More blood flows to the capillaries near the skin surface, increasing the skin temperature 1More heat is lostthrough convection and radiation 1

(iii) The rate of urine formation at rest is higher than that during heavy exercise 1More water is lost by sweating during heavy exercise 1The water potential of the blood drops .Thus more water is reabsorbed b collectin duct of the kidne .1

Total: 9 + 1 marks

10. (b) (i) Below 35C (-10-35C), the rate of carbon dioxide uptake increases with an increase intemperature .Above 35C (35-47C), the rate of carbon dioxide uptake decreases ..

(ii) The biomass will decrease .because the rate of respiration is faster than the rate of photosynthesis ..There is a net consumption of food / organic matter .(iii) 30-32DC .(iv) When there is light, stomata of the plant open .When air temperature is high, transpiration is fast .

A lot of water evaporates from mesophyll cell surface and carries heat away .Total: 9 marks

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2008 !Ell G=2008 Biology Paper 2

." . Question No. Key Q ue stio n N o. Key1. C (57) 31. *2. D (49) 32. D (53)3. D (62) 33. B (43)4. D (64) 34. A (47)5. A (95) 35~ C (62)6. A (77) 36. B (63)7. D (52) 37. A (90)8. D (52) 38. C (85)9. B (l9) 39. A (81)10. B (78) 40. C (75)11. A (51) 41. B (55)12. * 42. B (16)13. B (36) 43. A (9)14. A (51) 44. D (66)15. C (51) 45. A (30)16. B (58) 46. D (68)17. B (52) 47. D (46)18. C (49) 48. B (89)19. A (71) 49. C (53)20. C (56) 50. C (62)21. B (78) 51. C (53)22. A (88) 52. B (46)23. D (90) 53. C (24)24. D (49) 54. C (61)25. A (65) 55. A (43)26. C (71) 56. B (4])27. A (83) 57. B (24)28. B (80) 58. A (61)29 . D (84) 59. A (71)30. e (66) 60. C (64)

* *~M~flII!J~ .This item was deleted.ff:t: MNf1g!l!i!mEJf1Eij}J/I"Note: Figures in brackets indicate the percentages of candidates choosing the correct answers.

l I ~ r l l . I i t J l . l M l ~ 1 I J J~~~~'Wm~~&~~~~a*~~~~~~m~~~~~~m~~~'~m~~m~~~J m lJjjJ: f l l I I J = * 0 t l t l . l j1 3 : * ~ . t 1 i ' ..t.~ ~ ~ m - : : fP J 8 '9 ~ E I 3 1li m - 5t I J ~ E I 3~ m 8 '9 m 7 J UJ ~ , *R m : : f ~ ~ ~ ~ ~ ~ ~ m l l i * ' . ~ ~ ' * ~ . ~ ~ ~ ~ ~ R N ~ . ~ . ~ m ' ~ f i m M ~ ~ f t ' m ~ : : f ~ : : f ~ E . = * a . M ~ ~ ~ ~ ~ K ~ . ~ : : f m ' m i l l f l ~ ~ ~ M.~~,tt~~~~'*$IJ~~~*~.~ili~~General note on item deletionIt isnormal for the HKEAA to delete a small number of items from its multiple-choice question papers ifthey proveunsatisfactory. In practice, there are a number of reasons why this is considered necessary. By far the mostcommon reason for deleting an item is that the item fails to discriminate between weak and able candidates - inother words, the majority of the candidates involved had to rely on guesswork in answering that question. If suchan item is retained, the measurement process is rendered less effective. Where items have been deleted inthe livepapers, they are still included in this series of publications. They are indicated as deleted items. Such items may bediscussed in the examination reports.

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Candidates' PerformanceBiology Paper 1This paper comprises a wide variety of question types, and a number of questions set on topics that are firstintroduced in the 2003 curriculum, such as the five-kingdom system, historical development of scientific ideas,experimental design and the concept of sustainable development. This paper also assesses candidates' ability toapply biological knowledge to solve problems related to diabetes, and their understanding about the enquiryprocess of science.Markers considered the paper appropriate with regard to the length, level of difficulty and balanced in terms ofsyllabus coverage.The following table shows the general performance of candidates on different questions and the popularity ofthe questions in Section B:

Question No. Popularity (%) Performance in GeneralI good2 Satisfactory3 Fair

Section A 4 Compulsory Satisfactory5 Satisfactory6 Satisfactory7 Fair8 80 Fair

* Section B 9 29 Satisfactory10 91 Good

'"A choice of 2 out of 3 questions.Candidates' performance on individual questionsSection A

Q.l (a) This question required candidates to describe the digestive function of liver. Most candidateswere able to mention the function of bile juice. However, some candidates failed to point out thatthe liver is the organ for producing bile juice and that bile juice is released into the duodenum. Afew candidates just recalled the functions of liver in general.

(b) Most candidates were able to state the functions of various secretions. However, spellingmistakes were still common, especially terms like 'peptides' or 'glycerol'. Some candidatesconfused sodium hydrogen carbonate with sodium hydroxide.

Q.2 (a) Most candidates were able to relate the folding with an increase in surface area, but many ofthem failed to appreciate that this helps to increase capacity of holding more neurones in limitedspace. Instead, some candidates simply mentioned a larger surface area for exchange ofmaterials. Some even thought that it would increase the speed of impulse transmission due to theincreased area.

(b) Most candidates answered this part correctly, though a few candidates gave wrong examples.Some candidates confused the usage of 'control' and 'is responsible for'.

(c) Most candidates were able to answer this part correctly. However, spelling mistakes occurredeven in simple terms such as 'motor area'.(d) Quite a large number of candidates were unable to mention the correct name.

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Q.3 (a) Most candidates were able to identify structure X. However, many of them misspelt the name.Many candidates were unable to describe the function of pleural membrane accurately. Theyfailed to mention that the pleural fluid is secreted by the pleural membrane and wrongly putdown 'the pleural membrane reduces the friction during breathing actions'.

(b) Many candidates could construct a correct flowchart, but quite a number of them missed out thestructure pharynx. Spelling mistakes were common.

(c) Poor. Many candidates failed to identify structure Y. Candidates wrongly thought that Y is the airsac. Though most of them were aware that the air sac is one-cell thick, they failed to relate this tothe absence of muscle in air sacs, and therefore it is incapable of constriction. Due to suchmistake, most candidates answered poorly in this question.

Q.4 (a) Many candidates could state the two kingdoms concerned. Spelling mistakes were prevalent.(b) Fairly good. Most candidates were able to point out the presence of cell membrane, but some of

them failed to give another cellular structure.(c) Fair. Some candidates wrongly thought that the purpose of adding iodine solution is for

detecting starch. Many candidates failed to express clearly the purpose of staining.(i)

(ii) Fair. Most candidates did not know the term 'cover slip', and they just made up the termby themselves, such as glass, glass slide, cover slide, etc.

Q.5 This question assessed candidates' ability to identify the xylem vessel and sieve tube from aphotomicrograph, and their knowledge of the structures and functions of the two tissues.(a) Most candidates were able to identify the structures correctly. However, a number of them gave

comparisons other than structural differences required in the question.(b) There are two structural features which are important in facilitating the role of xyJem vessels in

the transport of water. The thick cell wall is important in preventing the collapse of the xylemvessels during transpiration, where a negative pressure is setup. However, candidates held amisconception that a positive pressure was produced. For the importance of reduced cell content,candidates mixed up the concepts about resistance and friction, they thought both are the same.

(c) Satisfactory. Most candidates were able to mention that phloem is responsible for the transport ofsugars. However, many candidates were careless in reading the question. Instead of explainingthe importance of sugar to the growth of root, they just elaborated on the role of phloem to theplant.

Q.6 The performance was satisfactory in general.(a) Most candidates were able to use the concept of enzyme to propose a hypothesis for thecoagulation of milk. However, many candidates tried to explain the phenomenon rather than

proposing a hypothesis.(b) Similar to part (a), instead of providing the principle for the investigation, many candidates

simply explained the results of the investigation. It reflected that most candidates lacked theexperience of writing laboratory reports.

(c) Many candidates did not realised that the question is asking for the procedures of an experimentfor testing if the step boiling of milk is necessary for the coagulation of ginger milk curd. Thusmany of them failed to gave a suitable control for the investigation.

Q.7 (a) Many candidates correctly stated the increase in muscle mass as the answer. However, only someof them were able to provide proper explanation to associate this with the increased basalmetabolic rate after the training. They wrongly thought that the increased basal metabolic ratewas a result of increased muscle activity during training.

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(b) Poor. Many candidates were not aware that the lost of body fat implies a consumption of energy .reserve in the body, which is a result of a greater energy expenditure than energy input.Misconceptions were common as revealed by the answers written. Firstly, candidates overlookedthat fat is also one of the respiratory substrates. Secondly, some candidates still used 'bum' fatinstead of oxidation of fat in the respiration. Thirdly, when answering questions, candidatesconfused terms such as 'energy consumption', 'energy intake' and 'food consumption'.

(c) Good. Most candidates were ab le to answer the question correctly.(d) Poor. Candidates were unable to relate the cause and consequence, thus unable to state the

Significance of the increased stroke volume to a person's ability to perform more vigorousexercise.

Section B

Q.8 (a) The performance was fairly good.(i) Most candidates were able to plot the graph with suitable keys and labels. However, there

was still room for improvement for writing the title.(ii) Most candidates were able to describe the effects of increasing the amount of inorganic

fertilisers used on the yield of wheat. However, only a few candidates were able todescribe the effects of both variables, i.e. to include the effects of the presence offungicides on the yield of wheat.

(iii) Most candidates were able to describe how the excessive use of inorganic fertiliserswould lead to the leaching of fertilisers to surrounding aquatic habitats. However, theyfailed to explain the impact on the aquatic community in an organised manner. Manycandidates either misspelt the word 'leaching', or failed to express the concept preciselyand clearly.

(b) This part was poorly-answered.(i) The question required candidates to apply their understanding on the function of insulin to

explain the control and care of diabetics. Diabetes is becoming more common in HongKong, and is mentioned frequently by the media. However, most candidates wereunaware of the fact that diabetics fail to store glycogen due to their inability to secreteenough insulin or respond to insulin, failing to provide proper explanations. Some justcited the overdose of insulin injection from the paragraph, which was not the casementioned in the question. Many candidates even confused the functions of insulin withthat of glucagon, resulting in poor performance,

(ii) This question assessed candidates' understanding on the digestion and absorption ofvarious types of carbohydrates. It also tried to incorporate candidates' understanding ofthe topic to the care of a diabetic patient.(1) Many candidates were able to answer the question, though not all of them could

give a complete answer. Some confusion still appeared, such as 'starch is stored inhuman and can release sugar gradually' .

(2) Most candidates could answer this part correctly.

Q.9 (a) The performance was fair.(i) Most candidates were able to answer though some candidates still spelt the term

'vegetative propagation' incorrectly.(ii) Many candidates had difficulty in answering this part of the question. Some of them

answered the questions without quoting the related process in meiotic cell division.Others were not clear about the process or mixed up the terms, e.g. pairing of sisterchromatids instead of homologous chromosomes. Some just reiterated that gametes

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cannot be formed due to haploidy. Many candidates did not know that homologouschromosomes are paired up for meiotic cell division.

(iii) (1) Many candidates were able to answer the question, though not all of them couldgive a complete answer. Some simply recalled the features of a wind-pollinatingflower instead of listing the observable features from the photograph.

(2) Most candidates could answer part of the question. It showed that candidateswere unfamiliar with the topic. Some candidates only mentioned the procedureapplied to carry out self-pollination, or a simple treatment of cross-pollinationwithout specific parent plants. Most candidates were not aware that, other thantransferring pollen, wrapping the flower throughout the process is crucial.

(b) The performance was satisfactory.(i) (1) Most candidates were able to answer the question.

(2) Many candidates failed to state precisely that the flow is along the drop in bloodpressure.

(ii) Most candidates simply stated the heartbeat is the cause of the rhythmic changes butfailed to explain how it occurs. It indicated that candidates did not understand themechanism concerned. Some candidates wrongly thought that it was the contraction ofthe muscular wall of blood vessels that caused the changes in blood pressure.

(iii) The performance was satisfactory.(iv) This part of the question assessed candidates' understanding about the return of chemicals

from tissue fluid back to the blood circulation. Many candidates were able to provide thecorrect answer.

Q.IO (a) Many candidates were unable to point out that the increase in body temperature is due toa greater heat production than heat loss. Many candidates failed to use appropriatedeterminers such as 'more' or 'a large amount' in their answers.

(i)

(ii) Most candidates were able to mention an increase in blood flow to the skin and ways ofheat loss. However, some candidates still held a misconception that vasodilation would. ..

(iii) In general, the candidates' performance was good.(b) Satisfactory performance.

(i) Good. Candidates had no difficulty in reading data from the graph. However, somecandidates were weak in describing the curves with suitable details.

(ii) Good. However, some candidates failed to compare the rate of respiration with the rate ofphotosynthesis.

(iii) Poor. Most candidates were not aware that the optimum temperature for the production ofcrop is one with the biggest difference in rate of photosynthesis and rate of respiration.Candidates simply stated the optimum temperature for photosynthesis as their answer.

(iv) Many candidates were not aware of the importance of transpiration in prevent overheatingto plants. They also held a misconception that the cooling effect was brought about by thehigh specific heat capacity of water. In fact, it should be the high latent heat ofvaporisation that accounts for the cooling effect during evaporation of water.

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General comments and recommendationsThe performance on this paper indicates that generally candidates performed well on less demanding questionsthat required the recall of basic biological knowledge. The performance on questions that demand more abstractthinking and application of biological principles is less satisfactory, particularly in questions where coherentarguments and communication skills were needed. As many of the questions in this paper were set in novelcontexts and required integration and application of biological concepts, candidates with superficialunderstanding could not achieve high scores. This is particularly evident in QA (c), 6 (b), 6(c), 7 (d), 8 (a) (ii), 8(b) (i), 9 (a) (ii), 9 (b) (ii) and 10 (b) (iv).Many candidates did not have a good understanding of the nature and role of hypothesis in scientific inquiry,nor the skills for designing methods to collect evidence for testing a hypothesis. The performance on theunderstanding of the role of insulin in regulating blood glucose level was also unsatisfactory.A considerable number of candidates relied too heavily on textbooks and tended to recite textbook materialswith little selection or adaptation when answering the questions. This is revealed in their responses to thequestions on the process of role of liver in digestion, the importance of sucrose to root, and the procedure tocarry out cross-pollination.Spelling mistakes were still prevalent. Many candidates could not spell the following biological terms correctly:'glycerol', 'pleural membrane', 'pharynx', 'bronchiole', 'prokaryotes', 'protoctists', 'cover slip', 'glucagon','lymphocyte', and 'phagocyte'. Some candidates were weak in questions that are based on the interpretation ofdata, which have a greater demand on analytical skills.

Biology Paper 2There were 60 questions in this paper. The overall performance of candidates this year was satisfactory, withthe mean score being 35. The following items serve to reveal some of the common weaknesses of thecandidates:Directions: Questions 10 and 11 refer to the diagram below, which shows the arrangement of some

neurones in the nervous system:

r IJ ,r J

neuronessupplyingthe arm { ~---~ : e x

11. Which of the following is connected to the type of neurone which is the same as X?*A.B.C.D.

the skinthe pupila tootha taste bud

(51%)(40%)(4%)(5%)

This question assessed candidates' understanding about the components involved in a nervous pathway. Theywere required to identify the type of neurone to which X belongs to and hence, determine which option isinnervated with this type of neurone. Half of the candidates chose the correct answer, while 40% of thecandidates mistakenly chose the pupil as their answer. This showed that candidates were familiar with thechange in the pupil size with respect to light intensity, but often overlooked the fact that the effector responsiblefor such change is the iris muscle.

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Directions: Questions 13 and 14 refer to an experiment about osmosis. Three strips of the same size werecut from a fresh potato and immersed into sucrose solutions of different concentrations forfour hours. The experiment was repeated using a potato that has already been stored for acertain period of time. The results obtained are shown in the table below:

Concentration of Percentage change in mass of the stripssucrose solution (%) Fresh potato Stored potato

0 +20.0 + 25.05 +6.0 + 10.010 ~7.0 ~2.0

13. The dependent variable in the experiment is measured as the percentage change in mass of potato stripsbecauseA.* B .C.D.

the final masses of the potato strips are different.the initial masses of the potato strips are different.there is a significant change in the mass of the potato strips.the mass can be measured accurately by using an electronic balance.

(20%)(36%)(36%)(8%)

This question assessed candidates' understanding about the necessity of data treatment for comparing the resultswhen the parameter being measured cannot be standardised for the initial measurement. However, only aboutone-third of the candidates were aware of the reason why the dependent variable is measured as the percentagechange in mass. Many candidates simply attributed the reason to a significant change in the mass of the potatostrips. This reflected that many candidates had a poor understanding about the data treatment for thisexperiment.

14. Which of the following about the interpretation of the results is correct?

*A.B .C.D.

Water potential of potatoafter storagedecreasesdecreasesincreasesincreases

Explanationsome starch is converted to sugars during storagesome starch is used for growing during storagewater is lost through evaporation during storagethe permeability of cell membrane increases during storage

(500.4)(22%)(15%)(13%)

Although the majority of candidates could interpret the data correctly and identify the change in the waterpotential of the potato after storage, about one-third of them chose a wrong explanation to account for theresults. In fact, starch itself has little influence on the water potential of the potato. The decrease in waterpotential is either related to the decrease in the amount of water or the increase in the solutes inside the cells.

43. Which of the following are reasons why bacteria can evolve rapidly in response to environmentalchanges?

*A.B.C.D.

(1) They mutate more readily.(2) They have a short life cycle.(3) In each reproduction, they produce a large number of offspring.(1) and (2) only(1) and (3) only(2) and (3) only(1), (2) and (3)

(9%)(47%)(17%)(27%)

About 90% of the candidates regarded 'producing a large number of offspring' as a necessity for an organism toevolve rapidly. However, they overlooked the fact that bacteria reproduce by binary fission which results in twodaughter cells at the end of the reproduction. The rapid multiplication of bacteria is mainly due to the shortreproductive cycle. When other external factors are flavourable, they can reproduce exponentially. Candidatesshould read the question carefully and integrate knowledge from related topics to analyse the situation given.

2008 Biology Paper I Marking Scheme

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