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Comparison between DSE17, PISA15 and HKJSBO17

The figures show % of number of questions in each category, despite that one question may have more than one mark. Some items belong to two or more categories so the sum would be greater than 100%. All questions in a paper are counted including both the compulsory and optional questions.

PISA 2015 IB HL 2015 HKJSBO 2017 HKDSE 2017Science knowledge

Content 53.3% 72% 42% 86%Procedural 32.6% 28% 90.9% 16%

epistemic 14.1 3.2% 3.6% 4%Competency

Explain phenomena 48% 70.4% 18% 75%Design enquiry 21% 3.2% 18% 6%

Interpret data 30% 23.2% 64% 19%Cognitive demand* 1:30.4%

2: 61.4%3: 8.2%

1:63.2%2:26.4%3:7.2%

1:11%2:62%3:27%

1:57%2:36%3:7%

Problem complexity* 1:68.82:10.4%3:17.6%

1:13%2:56%3:31%

1:71%2:25%3:4%

*1 is lowest, 3 is highest

DSE2017 Paper detailed analysis1A 1B Physiolog

yEcology Micro

biologyBiotechnology

Science knowledgeContent 94% 80% 100% 67% 86% 100%

Procedural 8% 30% 22% 14%

epistemic 0% 10% 11%Competency

Explain phenomena 83% 60% 100% 56% 86% 89%Design enquiry 6% 10% 11%

Interpret data 11% 30% 33% 14% 11%Cognitive demand 1:69%

2:28%3:3%

1:40%2:50%3:10%

1-86%2-14%

1-22%2-44%3-33%

1-71%2-29%

1-67%2-33%

Problem complexity 1:81%2:19%3:0%

1:60%2:30%3:10%

1-100% 1-22%2-67%3-11%

1-86%2-14%

1-78%2-22%

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Item analysis of HKDSE2017 papers

Paper 1A

Q2. The answer B is wrong, because salivary amylase is present and still working in stomach [1]. Over 10% of amylase even passes through the stomach into the duodenum [2]. Food only stays in the mouth for a short time so the role of salivary amylase would be very little if it only works in the mouth. The answer should be D. Q3. ‘at the beginning’ is confusing as students may think that the reaction have started and produced some sugars. Why not using ‘before the experiment’? Actually starch solution and enzyme X should be tested before mixing, but it is repeating the tests of P and Q. This may be one of the reasons for having only 34% correct for such an easy recall of food test results. Despite that the answer can still be identified by elimination, a good question should have an answer that is unambiguously correct, rather than ‘the best’.

Q4. This item has only 23% correct. Below is an analysis done by HKEAA in the teacher seminar:

According to the above analysis by HKEAA, each tube may have four ‘purposes’ –pre and posttests for the two food tests, and a total of 16 ‘purposes’. This makes the question highly complicated and vague. Why not specifying the tests concerned, such as ‘the purpose of the post- test of iodine test’?

The ‘purpose ‘ of a setup can only be known by the one who designs the experiment. How can student guess the thinking of the experiment designer? The question should be written as ‘What is the role of the following setup in order to draw a valid conclusion about the action of enzyme X?’

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The answers provided are also found problematic:

A. Purpose of P is to show the result of iodine test if starch is present.It is considered correct according to the marking scheme. But the positive result of iodine test can be shown by the pretest of R and S. P is thus redundant.

B. Purpose of Q is to show that enzyme X alone cannot give positive result in Benedict’s test. It is considered correct according to marking scheme. Any sugars in enzyme X solution before the experiment should have been detected by pretest of R and S. It is also unnecessary to check if enzyme X will produce sugars on its own after 30 minutes – an unlikely and unreasonable hypothesis. Therefore tube Q is also redundant. C. Purpose of S is to show that enzyme X is denatured after boiling.It is considered incorrect according to the marking scheme. The purpose of S is to act as a control to R so that any differences in the results of these two tubes are due to enzyme action. This design has assumed that enzyme X will be denatured after boiling. In this respect, the answer statement is deemed incorrect since this is the assumption rather than the purpose. However, if the overall purpose of the experiment is to test if enzyme X will be denatured after boiling, the purpose of S is exactly that of the answer statement, while R is a control. So the purpose of tube S depends on the overall purpose of the experiment, but it is vaguely stated as to ‘investigate the action of a starch-digesting enzyme X’.

D. Purpose of water bath is to simulate the temperature of the human body. It is considered correct according to the marking scheme. But the question does not mention that enzyme X is from human body. The only correct purpose of a water bath at 37oC should be to maintain a constant temperature for the enzyme action.

Q16. The answer is D. However, C and D are only distinguishable by rote learning of the standard schematic diagram in textbook. Is it what we want students to do?

Q17. The answer is C. But guard cells contribute to support by closing the stomata so that less water is lost and mesophyll cells are kept turgid.

Q18. Answer is D. But A and C can be correct. There is ambiguity caused by the use of ‘because’, which has five different meanings in scientific explanation [3] :1. Psychological (intention, purpose)2. Causal (mechanism)3. Nomological (explained by laws and theories)4. Darwinian (selective adaptation in evolution, ultimate cause)5. Functional explanation (A exists because it has function B.)

A. Veins have a large lumen because the blood pressure inside them is low

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This is considered incorrect according to the marking scheme. But this can be a correct functional explanation : Veins have large lumen that functions to return the low-pressured venous blood to the heart.

C. The aorta has the highest blood pressure because it supplies blood to the whole body.This is considered incorrect according to the marking scheme. But this can be a correct functional explanation: Aorta has the highest blood pressure by which it can supply blood to the whole body. An explanation based on causal mechanism is: The aorta has the highest blood pressure as a result of receiving blood directly from the left ventricle. This highlights how different meanings of ‘because’ affect the ‘correct’ answer.

D. The capillary network is a suitable site for material exchange because capillaries have the thinnest walls.

This is considered a correct answer according to the marking scheme. But it is correct only when ‘because’ is interpreted as causal explanation – The capillary network is a suitable site for material exchange as a result of its thinnest wall.

Paper 1BQ2. Marking scheme is as follows:

A softer pineapple is a result of water moving out of turgid cells, but the cells may only loss some turgidity rather than become flaccid (no turgor pressure). Therefore, ‘flaccid ’ should not be an essential part of the answer. Mention of plasmolysis will get no mark. However, a cell becomes flaccid only when it is plasmolysed. If flaccid is a required answer, it is hardly understood why plasmolysis as a cause for being flaccid is not accepted. ‘Water moving out of cells by osmosis’ has already entailed the existence of water potential gradient according to the definition of osmosis. So it is redundant to require students to mention the water potential gradient.

Q3a. The arrows can represent any “process” - a bug jumping among flowers, the scent spreading among flowers, plant hormone for communication, etc. Why not specifying process X and Y as ‘reproductive process’ or even ‘two kinds of pollination’? Without such specification, the requirement of ‘cross pollination’ as the only answer is unjustified. Moreover, more flexible marking scheme is preferred, such as ‘transfer of pollens between plants’ and ‘insect-pollination’. The exam report said cross pollination is implied in light of process X. However, the question does not state these two processes are related, so there is no grounds to infer one process from another.

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Q3c. The marking scheme is as follows: Greater genetic variation (1) Variants would be candidates for natural selection (1)

The following is an answer shown in the teacher seminar that scored no marks:

Is it too stringent to require ‘genetic variation of offspring’? The exam report explains why adaptation is not accepted - variations may or may not adapt to the environment, but only provide variants for natural selection. So what is the benefit of natural selection? It is the adaptation produced by natural selection:

Variation natural selection adaptation to changing environment

Therefore, it is adaptation that makes process Y better than process X, while natural selection is only the mechanism. Therefore, it is hardly understood why adaptation is not accepted as the answer.

Q7a. It accepts only one answer – constant rate of respiration. But many other answers are acceptable: The amount of oxygen dissolved in water is negligible/The amount of oxygen used for respiration is negligible/The only gas in the bubbles is oxygen/The rate of oxygen production is proportional to the rate of photosynthesis/The bubbles do not get trapped in the funnel or escape out of the funnel, etc. It is unreasonable to use such a highly restrictive marking scheme when the answer is open-ended. Moreover, the assumption of a constant rate of respiration would not allow the calculation of the rate of photosynthesis without knowing the rate of respiration. A correct assumption for the calculation is that respiration rate is negligible and zero. The following is an example shown in the teacher seminar - it scored no marks. The student clearly knew that plants carry out both photosynthesis and respiration and there may be carbon dioxide in the air bubbles. But for this experiment, respiration had to be assumed not existing in order to calculate the rate of photosynthesis. The meaning is similar to ‘neglecting the respiration’. Therefore, this answer should score points.

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Q7b. The marking scheme only accepts temperature as the variable to control for. But temperature may not be a major confounding variable in light of the large beaker of water that has kept the temperature constant. On the other hand, CO2 concentration should be a more important confounding variable affecting the rate of photosynthesis. However, adding bicarbonate is not accepted as answer. The two reasons cited in the teacher seminar are: 1. CO2 content in water will not change much during photosynthesis; 2. Adding bicarbonate will vary the CO2 content and create another variable. The first reason is flawed. Natural CO2 content in water is low and will soon become limiting to photosynthesis under strong light (see graph below). Also, almost all experimental protocols of this kind will add bicarbonate into water. As for the second reason, it can be solved by adding the same concentration of ‘excess’ bicarbonate for each light intensity.

HKEAA seminar cited student answer as below:

Q9di.Marking scheme

However, JE vaccination is not recommended for travel shorter than a month.

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JE vaccine is recommended for travelers who plan to spend 1 month or more in endemic areas during the JE virus transmission season. JE vaccine is not recommended for short-term travelers whose visits will be restricted to urban areas or times outside a well-defined JE virus transmission season. [4]

Vaccination may be justified for travel to an area with JE outbreak. But the question only states ‘a country with many JE cases’.

Q9dii.

Marking scheme:

Both the question and answer are flawed. Not any travel advices are found about using insect repellent after visit to JE areas! Besides, JE will not transmit from an infected person to mosquitoes: Humans are incidental or dead-end hosts, because they usually do not develop high enough concentrations of JE virus in their bloodstreams to infect feeding mosquitoes [5].

Q.10aii

The question requires students to explain why tongue-rolling (TR) is dominant or recessive based on the data Sturtevant collected in 1940.

The marking scheme is:

However, according to Sturtevant’s original article [6], his did not aim to find out dominance/recessiveness of tongue-rolling but on the genetic influence of the trait. He only suggested that tongue rolling ‘may be due to a single dominant gene’ [6]. The reason why Sturtevant could not conclude on the dominance of TR is that the original data included crosses of non-tongue rollers (NR x NR) that produced about 30% TR offspring. If the data of NRxNR were considered, the suggested answer is flawed. It is problematic for the question to selectively use the data of Sturtevant to reach a conclusion he did not make!

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Q. 10b This question claimed that in 1965 one new finding was obtained: NR xNR30% TR. Students are asked to explain whether this ‘new’ finding would support Sturtevant’s conclusion in 10aii. However, we found no article in 1965 on tongue rolling, but only Sturtevant’s book A History of Genetics [7], where Sturtevant cited his own work in 1940. So both the data in 10a and 10b are from Sturtevant’s article in 1940, which is nothing about one new finding rejecting another. The question has distorted the history and Sturtevant’s work!

The exam report writes:

It is correct to use the same logical deduction in 10a to reach the conclusion that NR is dominant, if only the data in this question are considered. The question is not asking to draw a conclusion based on the data in 10a and 10b. Besides, the report commented that students should look at the proportion of offspring, but proportion is rejected as the answer in 10a. That seems contradictory. Q10cii. The question provides further data on tongue-rolling using identical twin study:

Students are asked to explain how the data that supports the following two conclusions and the marking scheme is:

The study was done by Reedy and others [8] and the original set of data is as below :

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The data included both monozygous (identical) and dizygous twins. Reedy found that the % concordant of monozygous twins (88.5%) was significantly larger than that dizygous twins (77.3%), thus concluding that tongue rolling is mainly genetically determined. The question omitted the data of dizygous twins and asks student to make conclusions based solely on monozygous twins, which is flawed. A high % concordant (82%) in identical twins is not conclusive since it may be a result of the environment - the twins are living together. Only by comparing with dizygous twins can the effect of the environment be controlled. Therefore, the answers are incorrect. Q11. The essay question consists of two main parts:

a. How lymph is formed from blood and returned to the blood circulatory system Marking scheme:

It is undesirable for an essay question to allocate 5 out of 8 marks (plus 3 communication marks) to the direct recall of the processes of lymph formation and transport. The majority of marks should be given out in (b), where the concepts are applied to solve the problem.

The marking scheme represents the standard textbook answer, but it is wrong in light of the latest research. Fluid filtration is found occurring in both the arterial and venous ends of the capillary and lymph moves along lymph vessels by contraction of the lymph vessel itself [9]. It is understood that secondary biology may not be able to catch up with the advances in knowledge, but cautions should be taken as much as possible to avoid reinforcing misconceptions.

b. Is the claim valid: lymph massage can improves circulation of lymph and reduce body weight ?

Marking scheme:

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More marks can be allocated to this part since it assesses the application of concepts rather than direct recall. This is an open question and the marking scheme has to be more open. For weight reduction, more alternative answers should be considered: improving absorption and transport of fat through lacteal, reducing body fluid through urine after excess tissue fluid is returned back to circulation, and even improving immunity through lymph nodes [9][10]. It is called into doubt that lymph vessels are too deep inside body so that massage is difficult to improve circulation. The effect of lymph massage on reducing edema is well proven [11]. A better answer is ‘lymph massage can only help with circulation when a strong enough pressure is applied to the body parts since the lymph vessels are usually situated deep inside the body.’

References[1] Smith, M.E. (2010). The mouth, salivary glands and oesophagusDownloaded from https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/alpha-amylase[2] Fried M1, Abramson S, Meyer JH. (1987). Passage of salivary amylase through the stomach in humans. Downloaded from https://www.ncbi.nlm.nih.gov/pubmed/3652896[3] Bird, A. (1998). Philosophy of Science. Montreal: McGill-Queen’s University Press.[4] CDC.(2015) Japanese Encephalitis Vaccine.

https://www.cdc.gov/japaneseencephalitis/vaccine/index.html[5] CDC.(2015). Transmission of Japanese Encephalitis Virus. https://www.cdc.gov/japaneseencephalitis/transmission/index.html

[6] Sturtevant, A. H. (1940). A new inherited character in man. Proceedings of the National Academy of the USA, 26(2): 100-102. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1078012/[7] Sturtevant, A. H. (1965). A History of Genetics. Harper and Row, New York, NY.[8] Reedy,J. J., Szczes, T. & Downs, T.D. (1971). Tongue rolling among twins. Journal of Heredity, 62(2), 125-127.[9] Kirk, C. H. et al. (2015). Lymph formation, composition and circulation: a proteomics perspective.

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International Immunology, 27(5). Downloaded from https://academic.oup.com/intimm/article/27/5/219/749294[10] https://medicalxpress.com/news/2016-09-immune-major-role-body-weight.html (immunity and body weight)[11]Oliver Leduc, P. T. et al. (1998).The physical treatment of upper limb edema. Cancer, 83(12)Downloaded from https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-0142(19981215)83:12B%2B%3C2835::AID-CNCR36%3E3.0.CO;2-V