Biology
© International Baccalaureate Organization 2020
International Baccalaureate® | Baccalauréat International® | Bachillerato Internacional®
November 2019 subject report
Biology
Contents
Grade boundaries
3
Internal assessment HL/SL
5
Higher level paper one
14
Standard level paper one
16
Higher level paper two
19
Standard level paper two
24
Higher level paper three
27
Standard level paper three
36
Page 2 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Grade boundaries
Higher level overall
Grade:
Mark range:
1
2
3
4
5
6
7
0 - 15
16 - 27
28 - 41
42 - 54
55 - 67
68 - 80
81 - 100
1
2
3
4
5
6
7
0 - 14
15 - 26
27 - 41
42 - 54
55 - 65
66 - 78
79 - 100
Standard level overall
Grade:
Mark range:
Internal assessment HL/SL
Grade:
Mark range:
1
2
3
4
5
6
7
0-3
4-6
7 - 10
11 - 13
14 - 16
17 - 19
20 - 24
1
2
3
4
5
6
7
0 - 10
11 - 14
15 - 18
19 - 23
24 - 29
30 - 34
35 - 40
1
2
3
4
5
6
7
0-7
8 - 10
11 - 13
14 - 18
19 - 22
23 - 27
28 - 30
1
2
3
4
5
6
7
0-8
9 - 16
17 - 26
27 - 36
37 - 45
46 - 55
56 - 72
1
2
3
4
5
6
7
0-6
7 - 12
13 - 20
21 - 26
27 - 31
32 - 37
38 - 50
1
2
3
4
5
6
7
0-6
7 - 13
14 - 20
21 - 26
27 - 31
32 - 37
38 - 45
Higher level paper one
Grade:
Mark range:
Standard level paper one
Grade:
Mark range:
Higher level paper two
Grade:
Mark range:
Standard level paper two
Grade:
Mark range:
Higher level paper three
Grade:
Mark range:
Page 3 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Standard level paper three
Grade:
Mark range:
1
2
3
4
5
6
7
0-4
5-9
10 - 14
15 - 18
19 - 22
23 - 26
27 - 35
Page 4 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Internal assessment HL/SL
Range and suitability of submissions
The schools presented a large range of inventive and original investigations. Many were a real pleasure to
read. However, while fewer and fewer schools are submitting work that is entirely unsuitable or overlysimplistic, we are also missing some of the original and more creative labs we saw at the start of this
programme. For example, more and more labs are various versions of enzyme labs/inhibition labs. One of
the most common statements teachers are receiving in their feedback is that the investigations too
frequently mirror one of the prescribed labs, such as a lab on surface area and diffusion. This impacts
particularly on Personal Engagement.
Overall, most of the work was of a suitable standard.
Consideration of safety and ethics seemed to be less of a problem this session, though there are still those
schools using pathogenic microbes or incubating microbes too close to human body temperature.
There were some trivial investigations that were not of the appropriate level for the IB biology course and
some with little or no biological content at all (e.g. The price of a pen versus ink solubility) especially when
investigations are more in the realm of psychology or geography than biology. The vast majority of the
schools did provide appropriate material.
Once again, very few simulations were presented though the numbers of databased investigations seem
to be still increasing. Those involving modelling remain very rare. There is material posted on MyIB
including some exemplars that concern these approaches. We hope that they may clarify their use and
how they are marked.
or who used the Microsoft
Word comments function to annotate electronically submitted work, were most helpful. Examiners found
it less helpful when comments were grouped at the beginning or the end of the work. It was not
immediately obvious what the teacher was referring to in these situations.
A few samples were uploaded with pages missing. Some were scanned in black and white, so it was
impossible to understand colour coding used on graphs. The responsibility is with the school to ensure
that uploaded material is complete and legible.
A frequent problem encountered was teachers who did not annotate or comment on work at all (i.e. an
s
, if possible, to support the teacher.
Some samples were clearly marked by several teachers who worked in the same school. This is very good
practice. However, it was also possible to observe some schools where there were clearly several teachers
not cross moderating their samples.
The samples should be completely anonymous. Moderators were still finding candidate names, teacher
names, school names and other forms of identification on the uploaded material. Sometimes the
oderation, which is quite good
compared to previous sessions.
Page 5 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Moderators also noted that there were errors of judgement being repeated by schools that had received
feedback in previous sessions. It is most important that the feedback gets to the teachers concerned by
Candidate performance against each criterion
The application of the assessment criteria by teachers was generally satisfactory, though often
overgenerous, sometimes very generous. There were cases where teachers were pointing out significant
weaknesses in a criterion and then awarding the highest grade, therefore, more rigour is necessary when
applying the final mark. Teachers were, occasionally, considered too severe.
Evaluation is still the weakest criterion for many. This criterion is difficult and it does discriminate between
the candidates. For many moderators Analysis was also a criterion that needed more attention. Many
candidates were happy to leave the processing at the level of calculating means and standard deviations.
Personal engagement (PE)
Some form of personal significance was expressed in most cases. While many candidates were clearly
always been interested
The originality of the exploration was mostly acceptable and sometimes exceptional. There were,
however, too many cases of classic investigations being used with little or no attempt to modify them.
Personal input is evident in the persistence to collect data but also in the research for the background and
when establishing the scientific context of the conclusion, in following through the investigation and in
the choice of methods of analysis. Once again, this was clearly evidenced for many candidates. For others,
it seemed that after a good start with an interesting research question, they failed to follow through.
Personal input can be reflected at the simplest level by having completed the investigation, but those
following classic experiments, with no sign of application, cannot expect to score highly. There must be
some indication that there is a commitment to the investigation.
A number of moderators observed that teachers seem to be content with a statement of purpose at the
beginning of the report and then award the top marks. This criterion should be assessed holistically for
the entire report, so teachers need to look further for evidence when judging this criterion. A sub-section
devoted to Personal Engagement is not what is required. Furthermore, the students will probably need to
be taught how to express their personal engagement.
When marking this criterion, teachers should look out for the following:
•
•
•
•
•
•
•
•
•
•
•
A statement of purpose
The relationship with the real world
The originality of the design of the method (choice of materials and methods)
Evidence of trial runs
The difficulty of collecting data (evidence of tenacity)
The quality of the observations made
The care in the selection of techniques to process the data
The reflections on the quality of the data
The type of material referred to in the background or in the discussion of the results
The depth of understanding of the limitations in the investigation
The reflections on the improvement and extension of the investigation.
Page 6 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Because of its holistic assessment marking this criterion will overlap with components of other criteria.
Exploration (EX)
Moderators frequently commented that the research question lacked sufficient focus to obtain the highest
mark band. Scientific names were not always used and the range of the independent variable was
concentrations of an iron
name of the iron supplement selected, the range of concentrations used and which specific enzyme(s)
were used. It turned out that the enzyme was a lipase. The source of the lipase could also have been
included (e.g. porcine pancreatic lipase) and its substrate (in this case bovine milk fats). A research
question could also include how the measurements will be taken by introducing the dependent variable.
In this case it was by monitoring changes in pH levels.
many seemed to be satisfied with less focus
in the research question.
The requirements for the background are that it needs to be focused and contain relevant information
that is clearly linked to the research question. There were many cases of superficial or irrelevant material
taken from a standard textbook. Sometime candidates were citing material that was not from reliable
scientific sources. In the background, the independent variable also needs to be justified. For example,
why was the distance 0-30m from the low water mark used? The dependent variable needs to be
explained and linked to the investigation. For example: How is the change in pressure that is measured,
related to the activity of catalase? The discussion of controlled variables is needed to demonstrate that the
student appreciates the other factors that may impact on the experiment. Uncontrolled variables, for
example room temperature, may have a significant impact; they need monitoring. One cannot assume
that putting the experiments in the same place is enough and setting the air conditioning in a room is
often inadequate. Control experiments needed to be considered more frequently. Control experiments
reveal when an uncontrolled variable is having an impact on the measurements.
There was an increase in the number of candidates submitting databased investigations and these require
a different approach for the assessment of exploration. Generally, insufficient attention was given to
sample selection, as a clear explanation of this is the essential design component of the investigation.
Most of these types of investigations required a type of stratified sampling but this was rarely explained
or evaluated. However even if the sampling was systematic (for example selecting specific countries when
studying the epidemiology of a disease), the method used was rarely explained.
The methods were either written in prose or recipe style. Both were acceptable. Where the method was
not clear it affected both the Exploration and Communication criteria. The weaker submissions tended to
be from candidates who investigated a topic in which causal relationships were difficult to confirm and a
large number of controls were missing. For example, human physiology studies with limited data sets and
poorly controlled variables.
When marking this part of the criterion teachers should look out for the following:
•
•
•
•
•
The protocol for collecting the data
The range and intervals of the independent variable
The selection of measuring instruments (where relevant)
Techniques to ensure adequate control (fair testing)
The use of control experiments
Page 7 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
• The quantity of data collected, given the nature of the system investigated
• The type of data collected
• Provision for qualitative observations
Safety, ethics and environmental impact needed to be addressed in a large number of investigations. It is
true that some investigations may not have had any issues in these areas but there were plenty that did
and yet the candidates showed little or no evidence of concern. It is not sufficient to identify potential
areas where safety is an issue, there needs to be an indication of how the issue is avoided. All too often the
issue of safety was treated without much thought.
There were some cases of unethical treatment of animals. In one example a muscle was extracted from a
shellfish. The animal was alive. The candidate seemed to think it was acceptable because it had been
bought from a fishmonger and only one had been used. This type of work will be raised as an exception
and will be dealt with by the IBO ethics unit.
Though there were less problems with inappropriate investigations involving microbes there were still
some that approached them without adequate consideration of safety. Even if the microbes being
cultured were not pathogenic, it does not mean that any which contaminated the plates were harmless.
All microbes should be treated as potentially harmful. Furthermore, it is good practice to seal the lids on
the dishes with adhesive tape. This prevents them being accidentally opened. However, they should not
be taped all around the lid. This will encourage the growth of anaerobic bacteria, some of which can be
serious pathogens.
• The following guidelines should be applied:
• Only culture known non-pathogenic strains of microbes. For example, do not culture from hands or
swabs of door handles.
• Do not test for antibiotic resistance. There are enough antibiotic resistant strains circulating in the
environment without more being selected for.
• Apply strict rules of hygiene and aseptic techniques.
• Do not culture microbes at 37°C. Incubation should be carried out below 30°C; around 25oC is ideal and
many safe strains of bacteria, e.g. Escherichia coli K12 will grow well at this temperature, albeit more
slowly.
• Always label cultured plates so they can be clearly identified and never open them for inspection.
• Tape the lids on but do not tape all the way round a Petri dish. Taping all around the dish encourages
anaerobic conditions that are best avoided.
• Never assume that what is growing in the culture is the strain that was inoculated, even if nonpathogenic strains have been used.
• Always sterilise used cultures and dispose of the cultures using local health and safety regulations.
The use of consent forms with human volunteers should be systematic. This is an essential ethical practice.
The use of body fluids (urine, blood, saliva) is unacceptable practice. Human milk presented an interesting
dilemma in the May session this year. Milk is a body fluid and, as such, needs to be treated with precaution.
Milk from other animals should be processed so it is fit for human consumption then it would be
considered safe for use in the lab. Human milk, if it is obtained commercially, should also be safe.
Generally, the disposal of waste gets poor consideration.
When assessing safety, ethics and environmental issues, teachers should watch out for the following
during the experimental phase. Students will need guidance. In the written reports evidence for the
consideration of safety, ethical practice and environmental impact can be found as follows:
Page 8 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
• Evidence of a risk assessment
• An appreciation of the safe handling of chemicals or equipment (e.g. the use of protective clothing and
eye protection)
• An appreciation of the particular safety issues when working in the field
• Consideration of basic hygiene
• The application of the IB animal experimentation policy
• A reasonable consumption of materials
• The use of consent forms in human physiology experimentation and a consideration of the welfare of
the volunteers
• The correct disposal of waste
• Attempts to minimise the impact of the investigation on field sites.
Analysis (A)
The presentation of raw data was generally accurate but qualitative observations were often missing.
Qualitative observations are expected to accompany the raw data. Their impact will depend upon the
nature of the investigation, for example, fieldwork should always have a site description which could take
the form of maps, sketches or photographs with annotations. It was found that the qualitative
observations were sometimes made and then completely ignored during the discussion of the results.
There were investigations that generated only qualitative data e.g. the determination of starch levels using
students that this will impact heavily on the Analysis component. The students need to be guided towards
more quantitative methods. Colour changes can be tracked using colorimeters. Blood glucose testing
strips are sometimes used for tracking enzyme activity (e.g. the action of lactase on milk). Generally, the
range and sensitivity of these strips are too crude to give useable data.
Raw data from data logging may be expressed as a graphical readout. It should be accompanied by the
necessary information such as units and degrees of precision (if relevant) in the axis titles. These will also
impact on the Communication criterion. A candidate should present a representative sample of the raw
data, for example, when large amounts of data have been collected using data logging. A representative
graphical readout revealing how data is derived is acceptable. In this way the derived data becomes the
raw data.
Processing the data varied. Most candidates managed the basics, for example, means and standard
deviations, although there were a few who calculated these statistics for everything and anything. There
were still candidates who tried to apply standard deviation to a sample size that was too small (n<5). Error
bars do not have to be of the standard deviation. Maximum-minimum range bars can be used and this is
possible for samples of less than 5. Standard error of the mean is best used on large samples only (n>30).
There were examples of candidates calculating mean rates by averaging the data for all of the trail runs
and then calculating the mean from this. This is inexact. The rate for each run needs to be calculated and
then the mean is calculated from all the rates.
Candidates were still confusing R2 (the coefficient of determination) with r (the correlation coefficient). R2
can be used as an indicator of the goodness of fit of a trend line. It can approximate to the product moment
correlation coefficient if the trend line is straight but it is always a positive value unlike the correlation
coefficient, which can be negative.
Several candidates were using significance tests from t-test to ANOVA. Although good, they need to be
appropriately applied and there needs to be sufficient explanation for the processing to be followed. The
Page 9 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
use of programmes, such as Microsoft Excel, which produce a statistic, such as a p-value or a correlation
coefficient, are fine but the candidate needs to know what the value actually represents and what it
reveals. An ANOVA test (or F-test) may reveal that there is a significant difference between the treatments
but on its own it does not say which of them is different to which. Correlation coefficients should be
accompanied with a significance test as the significance of the correlation will depend upon the sample
size.
Basic measurement uncertainties were presented but not discussed. Candidates are expected to
appreciate the limitations of their instruments and, where they may have a choice, to select the
appropriate one. In biology, the biggest issue for uncertainties is in the variation in the biological material
(expressed as standard deviations, standard error or max-min range). Error bars showing variation were
frequently used on graphs but their significance, or even what they represented, was often absent. In some
cases the error bars were incorrectly placed or they had no bearing on what had been calculated. While
students now include the standard deviations almost as a default, few can use these data to comment
specifically on variation.
There were cases of students removing outliers from their data during processing. The use of a statistical
tool can help identify outliers in a data set. This is useful but it should be used with caution. If an outlier is
identified, then it cannot be automatically excluded from the processing unless there are legitimate
reasons for it. For example, the reading corresponds to:
•
•
•
•
an observed error in manipulation
an observed error in the behaviour of the measuring instrument
a known change in the experimental conditions
a biologically impossible result.
Otherwise, excluding outliers arbitrarily amounts to cherry picking the data, which is not good practice.
The interpretation of the data was sometimes well presented after each set of data; sometimes it was
mixed in with the conclusion. In weak candidates the interpretation was a written repetition of the data in
the tables with no attempt to point out the trends or to compare data. The use of statistics may have been
satisfactory but they were not always well-interpreted. As with calculators, the use of a program like Excel
is useful but can lead to accepting values without truly understanding them. Often the interpretation was
handicapped by the limited degree of data processing. Some candidates wanted so desperately to
support their initial hypothesis that they ignored the evidence pointing to an inconclusive result.
Evaluation (EV)
This was the weakest criterion for many candidates. It is a difficult skill but some candidates just seemed
to hurriedly finish off the report. Schools may need to consider the impact of the deadlines for the internal
assessment of each subject, theory of knowledge and extended essays on the
workload.
Conclusions were not always supported by the data and explanations were missing. The candidates did
not always refer back to their research question at this point. Some candidates were rather over-optimistic
in their conclusions. They ignored their processing or did not want to accept their results because they did
not fully support the hypothesis but they would aim to put a positive spin on
evaluate the data in the light of a statistical result like the standard deviation. This was a point that clearly
discriminated between the candidates but teachers did not always spot it.
Page 10 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
For databased investigations, evaluation must also look at the validity of the sample in terms of how
effectively it addresses the research question. This was rarely done.
For a full discussion, an attempt to explain the results in a scientific context is needed and the moderators
noted that this was all too frequently absent or superficial, relying on untrustworthy on-line background
information.
The evaluation of methodology is still a challenge to most candidates. The consideration of the strengths
was frequently missed. Weaknesses were often restricted to procedural details or sloppy manipulation and
the level of impact on the conclusion was often not discussed. Sometimes the candidates were distracted
by less significant issues. Proposed improvements were sometimes unrealistic and often too vague.
Extensions were often missed or illogical, not following on from the investigation. Sometimes they were
nothing more than improvements to the current investigation. This was an area where moderators felt
that teachers were often marking over generously.
When assessing Evaluation of the investigation, teachers should look for the following:
•
•
•
•
•
•
•
•
•
•
A conclusion that is supported by the data.
A conclusion that refers back to the research question.
An explanation based upon a scientific context, where possible referring to literature sources.
A discussion of the strengths this might be quite general or implicit or it might refer to specific parts
that worked well or data that was consistent.
Discussion of the reliability or the data.
Identified weaknesses and limitations in the method and materials.
The evaluation of the relative impact of a weakness on the conclusion.
Sensible, realistic improvements
Details on the improvements (e.g. not just that the investigation needs to be repeated but how many
times)
Realistic extensions that clearly follow on from the investigation.
Communication (C)
The responses to the communication criterion were generally good. Those who communicated well were
candidates who had already scored highly in the other criteria.
The most common problems in the work were:
•
•
•
•
•
•
•
•
•
The use of whole pages for titles. This is not necessary.
Whole pages for a list of contents. This is not necessary at all.
Blank data tables presented at the end of the method section; this is unnecessary.
Repetitive tables, when one would do. There is often no need for a raw data table in addition to a table
with processed data.
Inefficient data table headers. The art of designing data tables needs to be taught. A hand drawn sketch
of the table layout should be considered first.
Raw data relegated to the appendix when there was no reason for it. This upsets the flow of the report.
Tables split over two pages or with a title on one page and the table or graph on the next.
Multiple graphs drawn when they could have been combined, this not only saves space but it also
improves comparisons.
Squashed graphs so the distribution of the data is difficult to judge. This is often due to the candidates
not reformatting the font.
Page 11 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
• Bibliography, footnotes, endnotes or in-text citation missing. This would lead to the work being
suspected of malpractice.
• References with an incomplete format. Sometimes just the URL was given with no date of retrieval.
• Scientific nomenclature was not always used and the formats were not always respected.
For graphs that result from data logging that are used to derive a value (e.g. a rate) one example can be
presented to explain the processing then the rates derived can be organised in a table and it can then be
treated as the raw data.
The format for the citations, when they were presented, was mostly correct. However, candidates often
missed the need to include the date of access to online citations.
Format of scientific names was sometimes incorrect (small case letter for species name and it should to be
presented in italics).
Units were occasionally missing or they did not accompany the data.
The use of non-metric units (e.g. teaspoons, cups inches or °F) was noted by moderators occasionally. This
was true even for schools in the countries that use the metric system. One can only suspect that some
methods were taken from an internet source without correct consideration.
Measurement uncertainties were sometimes missing.
The numbers of decimal places were sometimes irregular or they did not correspond to the precision of
the data.
In general, the reports were of a suitable length. There were no automatic penalties for reports that were
slightly longer, so long as the reports remained relevant and concise. If they were accompanied by
extensive appendices, where the raw data is stored, then this would impact on the mark.
Recommendations and guidance for the teaching of future candidates
• Teachers must read and act upon feedback that has been received from previous sessions.
• Teachers should visit MyIB to see updated examples of individual investigations that are considered
adequate (teacher support material).
•
investigation in the scheme of work.
• Present the criteria to the candidates early on in the course and use them for the assessment of practical
work.
• Explain the expectations of each component of each criterion.
• Counsel the candidate on the feasibility of their investigation, focusing research questions, safety, ethics
and environmental impact, use of statistical programs and the use and presentation of citations.
•
investigation.
• Teach the students how to express personal engagement in their investigation.
• Teach candidates how to design tables and draw graphs.
• Graphs should not be reduced to such a size that they become uninformative, simply to stay within the
page limit.
• It is not expected that full calculations be shown, examples will suffice and a worked example from a
calculation carried out on a spreadsheet or a programmable calculator will not be expected. However,
screen shots should be considered especially when using databases or simulations.
Page 12 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
• Candidates should not add on appendices in addition to a write up of about 12 pages and should not
send in excessive quantities of raw data from data loggers (although showing an example of how these
raw data have been processed will be needed).
• Reams of extra work should not be submitted. Teachers marking the work should annotate it if they
judge the processed results to be a true reflection of the raw data from, for example, a data logger.
• Teachers should add comments throughout the work (rather than grouping them at the beginning or
end) and apply the criteria rigorously.
• Teachers should ensure that the work is anonymous. The candidate name, the school name, and the
session numbers must all be removed before scanning and uploading.
Page 13 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Higher level paper one
General comments
Many questions in this exam performed well, with a high discrimination index and a majority of candidates
answering successfully. Comments in this report will be confined to questions that performed badly in
terms of discrimination, were criticised by teachers or revealed common faults in understanding.
The percentages of responses rating the paper at least acceptable were high for clarity, presentation,
readability, suitability and exclusivity.
96% of responses, thought the paper to be of an appropriate difficulty, with the remainder regarding it as
remainder regarding it as a little more difficult.
The areas of the programme and examination which appeared difficult for the
candidates
Nomograms, areas covering experimental work.
The areas of the programme and examination in which candidates appeared well
prepared
Pentadactyl limb, mRNA sequences.
The strengths and weaknesses of the candidates in the treatment of individual
questions
Question 5
Required the use of a nomogram, a skill which is specified in the context of BMI in sub-topic 2.3 of the
program. Fewer than half of candidates were successful. A common mistake was to read the body mass
index from the left-hand end of a line drawn to show the extent of normal body mass, rather than from
the actual scale of the index. This suggests that some candidates had insufficient experience of using
nomograms.
Question 7
Required candidates to deduce the amino acid sequence that would be translated from a base sequence,
using a circular version of the genetic code. Over 85% of candidates were successful, but the
discrimination index was very low. Some of the stronger candidates made mistakes, including reading the
mRNA base sequence backwards or using the genetic code diagram as though it showed anticodon
sequences rather than codons on mRNA. Reading the code from the outside of the diagram inwards, rather
than inside outwards, was perhaps a forgivable mistake but the answer that this led to was the least
popular, so most candidates realised that degeneracy of the genetic code is in the third base rather than
the first.
Page 14 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 9
The most poorly answered question on the paper, with the percentage of correct answers below the 25%
level that would be expected from guesswork. The question asked about the practical technique for
producing water free of carbon dioxide for use in laboratory investigations of the effect of limiting factors
on photosynthesis. This is one of the experiments that are compulsory for HL students. The technique of
boiling water to remove dissolved gases and then cooling it, is described in guidance for this part of the
program. It seems from this question that some candidates are not being given sufficient hands-on
experience of practical laboratory techniques.
Question 17
The most successfully answered, with over 96% of candidates recognising the wing bones. Inevitably, the
discrimination index was very low. There were some other questions in the exam that were perhaps too
easy and they therefore discriminated poorly: Questions 1, 11 and 14. Of course another conclusion from
these questions is that they showed encouragingly widespread understanding among students!
Question 19
Criticised for the quality of the images. They were indeed rather crude representations of the four plants
but, even so, more than three quarters of candidates identified the filicinophyte correctly. In the future
when exams are on-screen, colour photos will be possible, so image quality can be far higher.
Question 23
Found hard by candidates, with only 45% answering correctly. A low discrimination index shows that some
of the stronger candidates chose the wrong answer. The question was based on an Application in subtopic 6.4 of the program: Causes and consequences of emphysema. This was a multiple completion
question. Nearly all candidates knew that air pollution and tobacco smoke are causes, but they were
evenly divided over whether genetic predisposition is a factor. There are genetic links with some forms of
emphysema, so the expected answer included it as a cause. In retrospect, it was probably not reasonable
to expect candidates to know this and a multiple completion question was unsuitable.
Question 28
Another multiple completion question and was answered correctly by fewer than 40% of candidates. The
discrimination index was high, indicating that stronger candidates tended to select the correct answer. R
groups do not determine primary structure the reverse is true so we reject the first of the three answers.
R groups do not stabilise secondary structures such as beta pleated sheets, so we also reject the second
answer. The third answer was the only correct statement - R-groups stabilize further folding of the
polypeptide into a tertiary structure.
Question 39
Answered correctly by only 43% of candidates. It was based on the last understanding in sub-topic 11.3:
The type of nitrogenous waste in animals is correlated with evolutionary history and habitat. This is a part
of the program that is typically not well understood, so if time permits, a fuller treatment would be useful.
Adult damselflies excrete uric acid because they must conserve water and this nitrogenous waste product
can be excreted in a more concentrated form than ammonia.
Page 15 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Standard level paper one
General comments
Many questions in this exam performed well, with a high discrimination index and a majority of candidates
answering successfully. Comments in this report will be confined to questions that performed badly in
terms of discrimination, were criticised by teachers or revealed common faults in understanding.
The percentages of responses rating the paper at least acceptable were high for clarity, presentation,
readability, suitability and exclusivity.
95% of responses, thought the paper to be of an appropriate difficulty, with the remainder being split
fairly equally between much more difficult and much easier. 82% thought that it was a little more difficult
The areas of the programme and examination which appeared difficult for the
candidates
Nomograms, areas covering experimental work, facilitated diffusion.
The areas of the programme and examination in which candidates appeared well
prepared
Pentadactyl limb.
The strengths and weaknesses of the candidates in the treatment of individual
questions
Question 1
Only half of students successfully calculated the magnification of the image. This required measuring the
actual length of the scale bar and dividing it by the length that it represented on the micrograph. The
commonest incorrect answer was a tenth of the correct magnification, suggesting that candidates had
made the mistake of measuring the length of the scale bar in centimetres rather than millimetres. With SI
units of length, it is safest never to use centimetres, because all the prefixes then used vary by factors of a
thousand.
Question 2
Only about 40% of students answered this question correctly and the commonest answer was incorrect.
Potassium ions flow through potassium channels in axons by facilitated diffusion, not active transport.
They are pumped through N+/K+ pumps by active transport.
Question 9
There were a few complaints about the inclusion of a nomogram for determining body mass index
because of the sensitivity of some students to issues of body weight, but this is skill that is required by the
program. Fewer than 30% of students correctly determined the BMI. Many used the left-hand end of the
line indicating the position on the scale for the minimum BMI within the normal range, rather than the
scale itself. This suggests insufficient familiarity with use of nomograms.
Page 16 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 10
Only half of students chose the best answer, which was that extreme pH can alter the active site of all
enzymes. Answer B was incorrect because some enzymes have an optimum pH other than 7, for example
protease in the stomach.
Question 12
The discrimination index for this question was very high, showing that well-prepared students tended to
select the correct answer, but more than 60% of students chose an incorrect answer. Many thought that
carbon dioxide is a waste product of anaerobic respiration in humans, possibly due to confusion with
yeast.
Question 13
About a third of students answered this question correctly, so it was found difficult and the low
discrimination index indicates that some of the better-prepared students chose the wrong answer.
Generally, two types of explanation for statistics such as these are that the question tests an area of the
program to which teachers have devoted insufficient time or that the question contains ambiguities. In
this case, all of the four answers attracted significant numbers of answers and there were no obvious
ambiguities in the question. It was based on a skill in sub-topic 2.8 (Cell respiration) and was therefore
clearly justifiable in terms of the program. This therefore seems to be a part of the program that deserves
more attention. Students should know that a fluid is used in respirometers to absorb carbon dioxide and
that carbon dioxide is produced in respiration and oxygen is used. They should also know that in
germinating seeds there is an excess of respiration over photosynthesis.
Question 15
The rather low discrimination index of 0.24 shows that some students who were well-prepared overall got
this question wrong. Co-dominance is included in sub-topic 3.4 of the program and students were
expected to understand that a 1:2:1 ratio is indicative of this pattern of inheritance.
Question 16
This was another question where the most popular answer was incorrect. The percentage of correct
answers was only slightly above the guess-level of 25%. Perhaps students thought that the normal
phenotype must be due to a dominant allele and that was why they chose answer B. However, the
daughter on the left of the pedigree is normal but has two secretor parents, so the allele giving a normal
phenotype must be recessive.
Question 21
Students found this question easy and more than 90% answered correctly. Inevitably the discrimination
index was therefore low.
Question 26
Only a third of candidates could trace the movement of oxygenated blood from the lungs through the
heart. Perhaps candidates were used to a more stylised diagrams of heart structure than the realistic
version shown here. Students were expected to eliminate answers C and D because oxygenated blood
does not pass first through the right atrium. Even if they were unsure what part of the heart was
Page 17 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
represented by I, they could then choose answer B rather than A because blood passes from the atrium to
the ventricle, not vice versa.
Question 28
Students found this question hard and fewer than 30% answered it correctly. The concept of a threshold
potential that causes sodium channels to open is specifically included in sub-topic 6.3 of the program. A
threshold is a level that must be reached in order to progress. The most popular answer was D, which was
the peak potential of the action potential when the axon was at maximal depolarisation.
Question 30
This was another question where the success rate of candidates was hardly more than the guess-level of
25% and the most popular answer was incorrect. This popular but wrong answer confused levels of LH
with FSH. The two other distractors also attracted significant numbers of students indicating confusion
to a single error of understanding. The changes in level of each of the ovarian and pituitary hormones is
distinctive and candidates are expected to be able to identify any of the hormones from a graph such as
this.
Page 18 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Higher level paper two
General comments
More than 80% of teachers who commented on the question paper thought that the difficulty was
appropriate with the remainder thinking it too difficult, probably because of the data-based question,
which was certainly challenging compared to other recent questions. Two thirds thought that the
difficulty was similar to last year and as usual more teachers thought that the difficulty had increased
rather than decreased.
Teachers were asked about the clarity of wording, presentation of the paper, readability, suitability and
inclusivity. In each case, a majority of teachers rated the paper good or very good and nearly all of the
others thought that it was acceptable. One teacher thought that the clarity was poor and one teacher also
thought the readability was very poor and another thought it poor.
Few comments were made in individual questions and in no case were there multiple comments
indicating general unhappiness with a question.
The areas of the programme and examination which appeared difficult for the
candidates
Production of antibodies as a consequence of vaccination
Chi-squared tests
Structure of striated muscle
Differences in composition between blood in the renal artery and renal vein
The areas of the programme and examination in which candidates appeared well
prepared
Identification if recombinants in dihybrid crosses involving gene linkage
Hydrophilic and hydrophobic parts of phospholipids
Inheritance of ABO blood groups
Cladograms
The strengths and weaknesses of the candidates in the treatment of individual
questions
Section A
Question 1: Data based question on Lyme disease
(a)
(b) Here again about half of candidates were successful and either identified antibiotics or a named
antibiotic as a suitable treatment. Some candidates confused preventative measures with treatments
and suggested ways of avoiding contact with ticks.
Page 19 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(c) This was answered very successfully and more than 90% of candidates gave the correct months.
(d) The necessary skill in a question such as this is to pick out significant features of the data. Generally,
the most successful answers were ones based on both the life cycle diagram and the graph, as the question
indicated should be done. The life cycle diagram showed when adults must be present during the year
and helped in interpretation of data in the graph. Adults must be present in winter so apparent values of
zero on the graph should have been interpreted either as low numbers or as a lack of activity and therefore
little chance of sampling them.
(e) This question needed to be read carefully in conjunction with a part of the stem earlier in the question
(Scientists fear that global warming will change the distribution range of ticks). Then it became possible
to understand what was intended. Candidates were expected to base their answer on predicted changes
to the distribution through the year of both nymphs and adults as these are the stages that can spread
Lyme disease to humans. Nymphs and adults will be become active for more of the year, so Lyme disease
can be expected to increase.
(f)(i) This was more successfully answered with most candidates stating that high or increasing numbers
of nymphs were the reason for performing the experiment from May to July.
(ii) Success here depended on an understanding of how vaccination works. Most candidates had at least
some knowledge. A common omission was to say only that vaccination causes memory cell formation and
not antibody production. This ignored the fact that the dependent variable on the y-axis was antibodies
to B. burgdorferi in mice. A common fault in analysis of the data was to ignore the control results. These
showed that bites from infected tick nymphs caused a far smaller increase in antibodies than vaccination.
It was therefore the vaccinations and not natural spread of the pathogens from tick nymphs that was the
prime cause of antibody production.
(g) This was another part of the examination where many candidates needed to read the question more
carefully.
It asked about the state of infection of tick nymphs, but most candidates wrote instead about infected
Even so, most scores were low. The analysis was admittedly very challenging. As mentioned earlier, the
aim with data should always be to pick out significant features. In particular, the data should be used to
d vaccination of mice reduce infection in
as there are many reasons for how many tick nymphs had been found on mice and tested. A first stage
therefore was to calculate separately the infection percentage for ticks taken from control and vaccinated
mice, at Site 1 and also at Site 2. This led to the conclusion that vaccination reduced the infection rate
significantly at one site but not the other.
(h) By this stage some candidates were struggling with the question and did not manage to write a useful
synthesis. A wide range of valid arguments was seen in answers though, and the best showed a very
impressive grasp of the biology.
Question 2 Autosomal gene linkage
(a) Candidates should be encouraged to give the best answer in every case, not just something that is true.
The expected answer here was gene linkage, because the data shows that the two genes did not assort
Page 20 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
independently. Dominance versus recessiveness was another feature of the genes implicated but this
does not define the pattern of inheritance so well. Dihybrid was not accepted as an answer, because it is a
type of genetic cross experiment, not a type of inheritance.
(b) This was very well answered and most candidates picked out the two non-parental phenotypic
combinations that are recombinants. Answers showing recombined alleles were also accepted.
(c) An easy first mark was on offer here for deducing that the ratio differed significantly from a Mendelian
ratio. The second mark required some understanding of chi-squared testing. The expected number of
degrees of freedom is three, because this is a test of goodness of fit, rather than a test of association. Both
of these uses of chi-squared are included in the HL Biology program.
Question 3 Cladograms, variation and natural selection
(a) Most candidates had some understanding of what is indicated by the nodes and branches of a
cladogram. The most frequent idea was that cladograms show common ancestry. Few candidates
mentioned that either base or amino acid sequences are used to produce cladograms.
(b) This question was also well answered by most. A weakness in some answers was in how to refer to the
individuals who tend to survive and reproduce. To say that they have adaptations for survival is a circular
argument. It is better to say that they have adaptations to their environment or lifestyle or niche. An
example can often help to clarify an answer.
Question 4 Lipids and photosynthesis
(a)(i)
hydrophilic and hydrophobic.
(ii) This was also answered well by most candidates, though some omitted to mention that the double
bonds are between carbon atoms.
(b)(i)
acceptable answer.
(ii) There was a full range of answers from exemplary to thoroughly confused. The best answers tended to
be concise, stating how water is split to replace the electrons that have been excited and passed to the
chain of electron carriers by Photosystem II.
Question 5 Skeletal muscle
(a)(i) The only answer accepted here was nucleus. It was understandable for candidates to think that the
dark structures were mitochondria, given their shape and dense staining, but the scale bar shows that
some of the dark structures are over 30 micrometres long, which it too large for mitochondria. Candidates
were expected to recognise that the micrograph shows muscle fibres, and that muscle fibres are
multinucleate.
(ii) About half of candidates knew that the protein in dark bands that consists of thick filaments is myosin.
(iii) Many candidates were confused here and gave incorrect answers. The bracket label showed one
muscle fibre and this was the expected answer. Myofibril was an understandable incorrect answer but
myofibrils would be difficult to see in a light micrograph and the scale bar shows that the structures visible
here are larger. A common answer was sarcomere, but that structure extends from one light band to
Page 21 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
another along the length of a muscle fibre or myofibril, so the positioning of the label made it clear that III
was not a sarcomere.
(b) This was general well answered, with many candidates debating whether the tissue consisted of cells
based on its multinucleate nature and the considerable length of the subunits (whether or not the
candidate referred to them as muscle fibres).
(c) This was also generally well answered with some impressive responses from well-prepared candidates.
A few candidates wrote about the role of calcium in the presynaptic neuron rather than in the muscle
itself.
Section B
Question 6 was the most popular in Section B and question 8 was least popular but each of the three
questions was chosen by substantial numbers of candidates.
Question 6
(a) Diagram of DNA structure
Nearly all candidates scored at least one or two marks, but a demanding mark scheme ensured that only
accurate and detailed diagrams scored full marks. Common weaknesses were to get the name of the sugar
wrong, refer to the bases only by their initials, or omit to label hydrogen bonds. Poorer diagrams tended
to get the bonds between deoxyribose and other components of a nucleotide wrong or the bonds
between adjacent nucleotides. Most candidates knew that the two strands are antiparallel.
(b) Characteristics of eukaryote chromosomes
Answers here were very varied. A common misunderstanding was to regard a chromosome as a
condensed structure, visible with a light microscope, implying that chromosomes are not present unless
a cell is carrying out nuclear division. Chromosomes are of course continuously present in the nucleus of
a eukaryotic cell and we should regard the uncondensed state as normal as this persists longest and is
when the genes are transcribable. The best answers gave a clear account of both the structural and genetic
characteristics.
(c) Synthesis of polypeptides
This question gave candidates ample opportunity to show their depth of understanding and detailed
knowledge. There was perhaps too much focus on initiation in some answers with little else being
described. Full marks could be scored by a clear explanation of the cycle of events on a ribosome that
elongates a polypeptide. Reference to the roles of the A, P and E binding sites for tRNA was expected.
Some candidates wasted time by writing about transcription. The examining team did not consider this
relevant, as the question asked about synthesis of a polypeptide, not RNA.
Question 7
(a) Reasons for differences in composition between blood in the renal artery and renal vein.
Candidates found this question hard. It was not enough to state the differences the question asked about
reasons for them. Some candidates were unable to answer the question because of a lack of knowledge
who clearly were well-prepared wrote long accounts of kidney function without actually answering the
question. The mark most commonly awarded was for a lower concentration of urea in the renal vein
Page 22 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
because of its excretion in urine by the kidney. Some candidates also scored marks for differences in the
concentration of oxygen and carbon dioxide due to cell respiration in kidney tissue. Very few candidates
commented on variation in the differences in concentration of solutes such as sodium and chloride due
to the homeostatic activities of the kidney, or on reductions in the concentrations of chemicals such as
drugs or chemicals absorbed from food but not required and therefore not reabsorbed from filtrate in the
nephron. Candidates typically had a detailed knowledge of what happened at each stage of the nephron,
but not of what was being achieved overall by kidney function.
(b) Inheritance of ABO blood groups
This was generally answered successfully, with Punnett squares well drawn. A lower-case letter i was
expected as a symbol for the recessive Group O allele, rather than IO but as long as the candidate stated
that this allele is recessive, an upper-case symbol was not penalised.
(c) Control of the heart
This elicited some high scoring, well written answers, but also some confused ones. Stronger answers
made the point that heart muscle contractions are myogenic, with the pacemaker initiating each beat. The
spread of the electrical signal through the atria and then on to the ventricles was then described and also
external influences including signals from the medulla oblongata via nerves. The most common point to
be included in answers was the role of epinephrine.
8a) Diagram of flower structure
There were some excellent drawings of half-flowers, with candidates scoring full marks, but also many
partially-remembered versions with errors. Common faults were stamens that we
to other parts of the flower and confusion over the terms for female structures, especially ovary, ovule and
ovum. A few candidates drew the diagram but did not add labels. It was still possible to score marks for
recognisable features, but much easier to recognise structures if they were labelled.
b) Growth of the plant shoot apex
Answers were better than expected with most candidates referring to differential growth occurring as a
phototropic response and sometimes also control of growth by auxin. Fewer answers remembered that
growth is indeterminate and that mitosis is required to generate extra cells.
c) Movement of energy and inorganic nutrients in an ecosystem
Answers to this question were very varied both in content and structure. The best answers distinguished
clearly between energy flow, with losses at each trophic level, and nutrient recycling, with autotrophs and
saprotrophs playing key roles. Weaker answers tended to contain errors of understanding about energy
transformation and reasons for energy losses from trophic levels.
Page 23 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Standard level paper two
General comments
Thank you to all the teachers who submitted G2 forms. The percentages of responses rating the paper at
least acceptable were 96% for clarity, 99% for presentation,95% for readability, with the doubts perhaps
on the length of text in Q1, 97% for suitability and 91% for exclusivity, perhaps again due to Q1.
83% of responses, thought the paper to be of an appropriate difficulty, with most of the others thinking
paper, with the remainder being split fairly equally between much more difficult and much easier. In reality
The areas of the programme and examination which appeared difficult for the
candidates
• Definition of species in a novel situation.
• Topic 2 (Chemistry of life) (very centre dependent)
•
• The role of inorganic nutrients in ecosystems
The areas of the programme and examination in which candidates appeared well
prepared
• Cell theory and characteristics of living organisms (Q3)
• Natural selection (Q4)
• The genetics of blood grouping (Q6)
The strengths and weaknesses of the candidates in the treatment of individual
questions
Question 1 data analysis
(a) few were able to state that they were different species as they could not produce fertile offspring:
definition that most would be able to state but were confused by the unusual wording. Nearly all were
able to state that O.japonica had the lowest diversity index and most were able to compare and contrast
the trends.
(d) a few stated 25%, instead of 75%.
(e) most were able to gain 1 mark but missed the second as they just stated the converse of the first mark.
(f) most were able to state that the control was there for comparison.
(g ) this proved to be the most difficult question on the paper. Some wrote about impendent evolution of
O.rufipogan from the sub-species, rather than independent evolution of O.indica and O.japonica from
O.rufipogan. Very few gained all 4 marks. It was good to see some of the grade 7 candidates underlining
the binomial names. (it was not expected in this case).
Page 24 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 2 Biochemistry
There seems to have been a large number of schools who omitted this section as a disappointing number
of candidates left the question completely blank,
(a) few were able to state that a codon codes for an amino acid. A common answer that was not accepted
(b)(i) most had a reasonable attempt but included an amino acid after the stop codon.
(b)(ii) a common mistake was to make a mistake in the last codon.
(d)(i), a ringing of the bond and the corresponding functional groups was accepted, although technically
the bond should have been labelled as a line.
(b)(ii)
,
was too general.
(e) There were a few comments about 2e, as some teachers thought that too much was being expected.
In effect all that was required was the simple function enzyme or its specific action and the fact that the
silk was structural and that they were globular and fibrous respectively. Both of these are in the list of
proteins stated in the guide. Interestingly a large number confused rubisco with rhodopsin.
Question 3
Almost all candidates scored well in parts a and b.
(c) however, few could explain homologous chromosomes. Many were confused
in the stem and wrote about cells instead of the chromosomes. Weaker candidates confused the words
genes and alleles in their answers.
(d) was a simple anaerobic respiration question, asked in an unusual format. A surprising number
incorrectly thought that oxygen WAS required.
Question 4
(a)
, credit was given for descriptions and
too general.
(b) most were able to gain at least two marks in what was quite a straightforward question on natural
selection.
Section B.
Candidates had to select either Question 5 or Question 6. Question 6 proved to be the more popular.
Compared to previous years, this section was quite well attempted.
As in previous years, the better prepared candidates were seen to make a plan before starting, either on
the page with the Section B questions or on a separate page. This makes a logical answer more probable,
and the gain of the extra point for clarity.
Question 5
Cell membrane, classification and movement of energy and nutrients in an ecosystem.
Page 25 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(a)
attempt at a diagram of the membrane, but a significant number tried to draw a whole cell. Perhaps it
would have helped the candidates if the instruction to annotate was also included. When the instruction
(b) Most managed to gain at least two points, as there were a large number of marking points.
(c) The movement of energy was reasonably well understood, with most realising that it is linear, starting
candidates and the role and fate of the inorganic nutrients proved to be a good discriminator. Many drew
diagrams of very variable standard to show the movement of energy and nutrients. The clear ones were
credited.
Question 6
Blood clotting, the genetics of blood grouping and gas exchange.
(a) How the blood clots was a total mystery to a large number of candidates who had not encountered it
in their studies. Those who had been taught it, scored nearly full marks. Some, however, mixed up
thrombin and fibrin.
(b) This was generally well answered, with a large proportion gaining full marks. The command word was
However, a written explanation was also accepted. The symbols for the alleles used in the scheme were
expected, unless a clear key was included.
(c) This was a part that needed some form of plan before putting pen to paper, as many answers were far
too rambling and repetitive, requiring a lot of rereading by the marker, and thus the loss of the clarity
mark. There were really two parts to the question, an explanation of how air is moved in and out
(ventilation) and how the gases are exchanged between the alveoli and the capillaries. A large number
wrote about one, while completely ignoring the other.
Recommendations and guidance for the teaching of future candidates
Candidates should be reminded that answers may be amplified by the use of clear, annotated diagrams.
However, poor half-remembered diagrams will not gain anything. Diagrams must also be drawn boldly in
a dark pencil or pen. Papers are scanned in for marking and feint diagrams will not display. Equally some
candidates still attempt to write in light blue ink, which does not scan very well.
Many, mainly weaker candidates seem to fill up the first few lines by restating the stem of the question,
thus restricting the number of available lines, leading to them requiring an extra answer booklet.
Some candidates do panic when they see question 1. If this happens, it could be suggested for them to
start on section B, leaving sufficient time to go back to question 1 later. In section B, and in the longer
answers, for example, in 1 g) or 4 b), candidates should be encouraged to think of a plan instead of starting
ould be uppermost in their
minds. This also enables the answer to flow easily, requiring little or no rereading by the examiner,
meaning that the candidate is more likely to gain the clarity mark for section B.
Page 26 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Higher level paper three
General comments
There were almost no reports of candidates failing to answer Section A or attempting more than one
option in Section B, but there seemed to be more candidates leaving blank answers, especially in Spanish
and German. Although most responses were very legible, the number of responses that were harder to
read seemed to have increased. The vast majority of candidates comply with the instructions, but there
are still some taking the risk of writing outside the prescribed boxes and having part of their answers not
being seen on screen by examiners. Often, especially in German, time and space were wasted by repeating
part of the question.
The majority of candidates chose either option C or option D, much fewer option A, and only very few
option B, mainly in Spanish.
The percentages of responses rating the paper at least acceptable were high for clarity, presentation,
readability, suitability and exclusivity.
91% of responses, thought the paper to be of an appropriate difficulty, with the remainder split evenly
between regarding it as too difficult and too easy. 98% thought that it was a little easier, a little more
The areas of the programme and examination which appeared difficult for the
candidates
As always, there is a problem of not reading questions, complying with command terms, and focusing
answers. There were also more candidates who appeared to have difficulty in interpreting the questions,
thus answering about something else (see the section about specific questions). Many candidates seemed
to have some difficulty in using appropriate terminology, like "species" instead of individual organisms
and/or
Many provide a multiple choice to the examiner when the question specifies the number of required
elements, written in bold letters (only the specified number of elements first appearing will be marked
then). The biological knowledge of those writing in German still showed major gaps for higher level
candidates.
Section A caused problems for many candidates, more notably in Spanish and even more in German, with
too many candidates having no idea of the mandatory practicals that they should have carried out during
their program. Thus, skills that should have been developed appeared to be absent, such as understanding
of osmolarity and related graphs. In German, candidates had difficulty interpreting the questions correctly;
databased questions continue to pose a major hurdle, as often all questions in one section or the (whole)
option were interpreted as all relating to the graphs or the initial stem; also the conclusions based on the
graphs were often inverted, i.e. the cause was seen as the effect. In addition to the apparent lack of
leading to difficulties correctly interpreting the questions and inability to express themselves clearly in
German, often using Spanish sentence construction and vocabulary.
Areas showing main difficulties in Option A were visual stimuli, slow-acting neurotransmitters and, for
some, stimulant drugs; in Option B, understanding of reading frames was limited and the question about
fermenters was misinterpreted; in Option C, many candidates, particularly in Spanish, had little or no idea
Page 27 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
of feed conversion ratios (FCR); also the effects of shape and size of protected areas and characteristics of
eutrophic lakes caused difficulties; in Option D, explanation of severe protein malnutrition, identification
of endocrine glands and sources of vitamin D.
The areas of the programme and examination in which candidates appeared well
prepared
The options seemed to be more uniformly covered than Section A, with candidates demonstrating the
normal range of knowledge, from excellent to little or absent, but without any specific, outstanding
problems with the individual topics covered in this paper. The great majority of candidates do attempt to
answer all questions (except for what we mentioned about the Spanish and German responses), and the
long (last) question for each option was generally well attempted (see details in the next section). Many
candidates, except for what is mentioned above, were able to interpret graphs and images well and are
better at short theoretical questions. Topics that were generally well answered involve neural pruning,
courtship behaviour, effects of stimulant drugs (for some); marker genes, biogas fermenters,
bioremediation, use of viral vectors, use of DNA microarrays; niches, keystone and indicator species,
nitrogen cycle, capture-recapture method; the functions of the liver, defibrillation, mode of action of
steroid and protein hormones, control of ventilation rate. Option D was generally better than the others.
The strengths and weaknesses of the candidates in the treatment of individual
questions
Section A
Question 1
(a) Most candidates provided valid answers, but too many only considered the contrast part of the
question, sometimes with more than one element, and did not provide similar elements for the
comparison. There were a noticeable number stating that one was vertical whereas the other was
horizontal; as this was provided in the question, it was not considered as a valid answer.
(b) The majority provided a valid suggestion, but there were some unable to give a reason for their
choice of figure.
(c) The majority stated two valid elements. There are nevertheless some providing more (that were not
considered), and many used the word "amount", where "concentration" or "volume" should have been
used. Some named general variables that both mesocosms would be exposed to automatically as open
systems, such as CO2 concentration, wind, etc. Also, the majority wrote outlines instead of simply stating
variables as required by the command term; this was not a problem.
Question 2
(a) The majority of candidates could describe the trend in the data, but it was more difficult for some to
suggest why transpiration continued; some irrelevant answers were seen, including those only repeating
the question.
(b) Most could state the independent variable, but there were also too many unable to do so.
Page 28 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(c) A number of candidates could mention the use of a potometer, but a large number had difficulty
explaining how it worked. Those who had not performed practical 7 from the subject guide could not
answer. Too many confused potometer with respirometer.
Question 3
(a) The majority answered 0.36 mol dm-3, including units (correct answers were precise, as no others
within ±0.01 mol dm-3 were seen); some answered 0.4 mol dm-3, which, although an estimation, was not
taking the divisions on the x-axis into account; many other incomprehensible or approximate values were
seen, especially in Spanish, and some even provided an explanation instead of a numerical estimate.
(b) Better candidates predicted that the osmolarity would increase; although many were able to identify
that the cells would lose water, they equated that to a decrease in osmolarity, as if they had chosen at
random; those who had not performed practical 2 from the subject guide could not answer.
(c) Most candidates had some difficulty providing clear answers for this question, although many
mentions of being able to compare were seen.
(d) Most candidates with a general satisfactory performance or higher could answer that the cell would
burst or lyse, but many irrelevant answers were seen below that level.
Section B
Option A: Neurobiology and behaviour
Question 4
(a) The majority of candidates answered correctly.
(b) The majority could outline a feature of neural pruning.
(c) The majority answered correctly medulla oblongata.
(d) Candidates had more difficulty providing clear explanations, although most could relate to the need
for oxygen in cellular respiration. Some included irrelevant points regarding strokes. Few included
examples of how the brain uses energy.
Question 5
(a) Many candidates could draw correctly an arrow showing the direction of light, but some left the
space blank.
(b) Most candidates could identify the two cells, but a number of irrelevant answers were seen, mainly
from those who drew the arrow incorrectly in (a).
(c) A large number stated a correct receptor name along with its stimulus, but a number of incorrect
answers were seen.
(d) The majority of candidates had a lot of difficulty with this question, although some could provide
partly correct explanations and/or identify the optic chiasma. Most candidates could not use appropriate
terminology, confusing image with nerve impulses, did not take the different visual fields into account,
explain that each visual field projects images on either side of the eye/retina, and/or that nerve impulses
from the left side of the retina go to the left side of the brain or vice versa; many stated that information
from the right visual field is processed in the left visual cortex without further explanation.
Page 29 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 6
(a) Most could define a neurotransmitter, although many had difficulty in providing a clear answer.
(b) This question was difficult for the majority of candidates, although a certain number could partially
describe the effects of local anesthetics.
(c) Only a small number of candidates could describe the role of slow-acting neurotransmitters, many
only mentioning the release of second messengers.
Question 7
(a) The majority of candidates could describe courtship behaviour, mainly mentioning its inherited
component.
(b) The majority of candidates could completely or partly explain the implications of courtship behaviour
in natural selection; some confused behaviour with external features though.
(c) Most could outline operant conditioning, giving an appropriate example, but there were
nevertheless some answers confusing it with classical or reflex conditioning.
Question 8
A wide range of explanations were seen about the effect of a named stimulant drug. Most answers covered
general aspects, but some were very precise including cellular mechanisms whereas others could hardly
name correctly a stimulant drug.
Option B: Biotechnology and Bioinformatics
A limited number of candidates chose this option; some excellent answers were seen, whereas others left
many blank answers. It is therefore more difficult to generalize about the candidates' performance.
Question 9
(a) The few that could identify the first triplet gave the others incorrectly or not at all.
(b) A few gave the last statement related to the length to produce a polypeptide.
(c) There was general knowledge on marker genes but few with sufficient detail for a complete
explanation.
(d) Many were able to name a method.
Question 10
(a) Most provided reasonable suggestions.
(b) Most could identify ideal conditions.
(c) Most understood the basic characteristics of biogas fermenters and were able to provide a complete
distinction.
(d) This question was more problematic as conditions were given but without explaining how they are
maintained.
Page 30 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 11
The topic of bioremediation was generally well understood.
Question 12
(a) Most have some knowledge of biopharming and were able to give an example.
(b) Most candidates had at least a partial understanding of the use of viral vectors.
(c) Most candidates had at least a partial understanding of the use of the ELISA test.
Question 13
There was a wide range of quality of answers here, from quite complete to very confused, although most
were able to provide a few explanatory elements.
Option C: Ecology and conservation
Question 14
(a) A number of candidates understood the meaning of FC ratios, but only a limited number of
candidates could provide a complete answer.
(b) Although some very good evaluations were seen, answers to this question showed a lot of confusion
about food webs, many not even able to describe what a food web is.
(c) Most explanations were weak for this question; some had difficulty explaining their importance,
although many candidates minimally managed to define keystone species.
(d) Most candidates could provide a partial answer to this question, either by defining the niche, or,
inspired from a past paper, relating to the concept of fundamental and realized niche. A few excellent
answers were seen, including the principle of competitive exclusion and all dimensions of a niche, whereas
poorer answers confused niche and habitat.
Question 15
(a) Most candidates did well on this question, although many answers focused only on differences.
(b) Most candidates had an idea about microplastics/toxins getting concentrated along the food chain,
but it was difficult for many to provide a structured outline of plastic breaking into microplastics/toxins
and then being ingested by animals.
(c) The majority of candidates could state that indicator species are affected by environmental changes,
but it was difficult for many to clearly describe their use to monitor environmental conditions.
Question 16
(a) A number of candidates could state an advantage (mainly, organisms remaining in their own habitat),
but too many irrelevant answers were seen.
(b) A mixture of good and irrelevant answers were seen for this question; many candidates
misunderstood that corridors are barriers instead of being connections.
(c) A number of candidates could state the meaning of a high value of Simpson's index.
Page 31 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(d) The majority of candidates could provide an explanation about the shape and size of a protected
area, but some statements were very general and too vague, with very little on edge effect.
Question 17
(a) The vast majority of candidates identified iron correctly.
(b) A large number of candidates could outline a role of Rhizobium, and many complete answers were
seen.
(c) The vast majority of candidates related to eutrophication due to runoff of fertilizers, as in past
questions, and thus provided complete answers. They nevertheless did not realize/know that eutrophic
lakes may occur naturally under other high productivity conditions and didn't seem to fully understand
the meaning of bloom.
Question 18
The vast majority of candidates related to the capture mark release recapture method. Some provided
complete, logical and precise answers, whereas others omitted steps or details, such as counting the
organisms captured each time, and how the samples were captured. Many wrote "counting species"
instead of counting organisms. Examples of species were often inappropriate or too vague a group, e.g.
fish, as well as capture methods, e.g. quadrats. Others were confused using the formula.
Option D: Human physiology
Question 19
(a) Almost all candidates could make the distinction.
(b) The vast majority suggested a valid reason.
(c) Most candidates could provide an explanation, but many were only partial.
(d) Although some correct answers were seen, there is generally a poor knowledge of dietary sources of
vitamin D many indicated fish, rather than oily fish. Many suggested fruits or vegetables. As dietary
sources were required, sunlight, supplements or vitamin pills were not accepted.
(e) Many candidates could provide a valid symptom, but only a few could combine it with a valid cause,
confusing physiological causes and risk factors.
Question 20
(a) The vast majority provided a correct answer.
(b) (i) A very large number provided a complete description, others missed some elements; some
incorrectly stated that Kupffer cells take up erythrocytes rather than hemoglobin, whereas others
completed their answer with the fate of iron, amino acids and/or bilirubin, which were irrelevant for this
question asking to focus on the breakdown of hemoglobin.
(ii) The majority stated another function of the liver. Outlines were not that extensive, but valid statements
were nevertheless accepted.
(c) The majority provided a valid answer such as fibre, cellulose or bacteria. Some could not answer.
Page 32 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Question 21
(a) Most candidates correctly stated that improved awareness in general or improved diets or more
exercise resulted in reduced deaths due to heart disease.
(b) The vast majority could outline the use of a defibrillator, although some provided rather vague
statements on its use.
(c)
The majority were able to fully explain the sounds of the heart.
Question 22
(a)
The majority provided a valid suggestion.
(b) Most candidates could distinguish the mode of action of steroid hormones and peptide hormones;
some answers were complete whereas other were only partial as they either were not presented logically
with equivalent comparison elements or didn't use appropriate terminology, such as plasma membrane.
(c) The majority of candidates identified the pituitary gland as being endocrine and provided a valid
reason, but there were some confusing exocrine and endocrine.
Question 23
Most candidates generally provided good, and many complete, thorough explanations, but there were
also a number of answers lacking sufficient details or containing diverse inaccuracies. Some candidates
explained changes in heart rate, which was irrelevant for this question.
Recommendations and guidance for the teaching of future candidates
Many recommendations from past subject reports still apply and are therefore repeated here. Those apply
to examination preparation, syllabus coverage, writing skills and examination techniques.
Preparing for the examination
• As usually recommended, the use of past papers and mark schemes is a valuable tool to prepare
candidates for the examination.
• Teachers and candidates should nevertheless be warned that it is counterproductive to rehearse or
memorize answers from past papers and/or manuals. The extent of the syllabus has limits and it is to be
expected that the same topics will be covered throughout the years, but each examination paper is
different in coverage and perspective. Past mark schemes are useful for familiarization to the paper
format, question style, expected vocabulary, depth and variety of elements to include in answers. It is
not because a new question shares a few words with a past question that the expected answer will be
the same.
Syllabus coverage
• It is important that schools include the recommended number of hours for a practical programme and
internal assessment, in the field or in the laboratory, and include the seven compulsory practical
experiments. It appeared, based on their specific answers to questions relating to section A that many
candidates/schools have not been covering the practical programme, at least sufficiently, especially in
Spanish and German.
• The syllabus has to be covered completely, including understandings, applications and skills, with links
to TOK and NOS when applicable.
Page 33 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
• Although it may not have applied to this paper, it is expected that all candidates comply with the
mathematical requirements for the programme, including the ability to calculate ratios and deal with
decimals. These could be practiced throughout the practical programme.
• A variety of practical examples, data and graphic presentations should be incorporated to the teaching
of various topics.
• Teaching of all understandings should be at objective level 3, when applicable.
• Teachers and candidates are encouraged to use multiple sources of reference.
Reading and writing skills
• Many candidates could have reached a better performance in this examination paper by reading the
questions more carefully and including more details in their answers. Something that seems obvious to
the candidate cannot simply be assumed by examiners, unless it is explicitly written. A school approach
to reading and writing into details, using specific vocabulary, could perhaps improve the situation.
• Candidates should be aware that command terms have sometimes a different meaning than they think
and should familiarize themselves with them during their course. Any "outline" question should never
be answered by one word. "Discuss" or "evaluate" questions, including data based questions, usually
require different perspectives to be taken into account, and "compare and contrast" usually require at
least one similarity and one difference. Teachers should use them throughout the course for their
exercises and internal tests.
• P
quantitative answer or the word "species" to designate individual organisms.
• Teach the vocabulary of biology as candidates need to use subject-specific vocabulary in their answers.
Teachers may choose to build up a glossary of terms used in the programme.
Examination techniques
• Candidates have a five-minute period before being able to start writing when they are handed Paper 3.
They should be aware of this and use this period to carefully read the questions and start mentally
planning their answers.
• Developing the habit of taking a little time to lay down and organize an answer's core elements would
improve answers and prevent omitting important ideas. Coach candidates on how to structure answers:
they should take time to consider what is relevant to the answer, leave out what is no longer relevant
(e.g. aspects from previous papers) and avoid repeating the same ideas. Encourage candidates to
highlight or underline the keywords in the question and plan their answers accordingly.
• Candidates should be encouraged to answer the questions they know and understand best at the
beginning of the exam. That way they do not lose out on marks because they spend too much time on
a more difficult question. They should nevertheless check that they did not omit answering any
question.
• It is unnecessary to repeat the question or stem in the answer box; this uses up time and space needed
to answer. As can be seen from available mark schemes, marking is based on facts and accuracy rather
than on style.
• The number of marks indicated in the right margin of the question paper is often an indication of the
expected details and number elements for a complete answer. Repeating the same thing many times
within an answer doesn't pay much though, elements have to be different.
• Different parts (e.g. (a), (b), etc.) of a question usually, but necessarily, share a common idea or topic,
and candidates are not expected to link them together, unless specifically requested to do so (e.g.
Page 34 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
•
•
•
•
•
Biology
"using all the data..."). They should read the question carefully to determine which part would relate to
a graph and which addresses only general knowledge.
With positive marking, candidates are given credit for what they have achieved and for what they have
got correct in an answer, rather than being penalized for what they have got wrong, providing there is
no contradiction within the answer. Leaving answers blank is therefore not a good strategy.
Bring a ruler and a square to the exam. This could help measure values on graphs with the required
precision.
Although this did not apply for this paper, respecting proportions in diagrams makes a difference. In all
cases, all drawings should be well annotated and labelled carefully.
Use of colour should be avoided as responses are scanned in black and white to be displayed on line for
examiners to mark them.
Candidates should not try writing outside the provided boxes, as this may not be seen at marking;
continuation answer booklets should be used instead. Most candidates make a sensible use of
continuation answer booklets and avoid using them for only one extra word. The best answers usually
fit within the space provided and very few gain additional marks from answers which extend into a
continuation booklet. An indication that an answer is continued should nevertheless be made in the
main booklet whenever a continuation booklet is used to make sure that the examiner will view it.
Page 35 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Standard level paper three
General comments
Very few candidates took option B. Attainment was lower in Spanish in general than the mean attainment.
The percentages of responses rating the paper at least acceptable were high for clarity, presentation,
readability, suitability and exclusivity.
91% of responses, thought the paper to be of an appropriate difficulty, with most of the others thinking
paper, with the remainder being split fairly equally between much more difficult and much easier.
The areas of the programme and examination which appeared difficult for the
candidates
Questions in Section A were directly linked to the required experiments. If candidates had carried out
these experiments during their studies, they had no difficulty in successfully answering the questions. It
was obvious from some of the vague and imaginative responses, that some candidates had no familiarity
with the required experiments and had little practical experience. In some cases, candidates scoring near
full marks on the rest of the paper were unable to answer these straightforward questions risking their
chances of a top grade.
A few candidates left Section A blank.
Incomplete answers were also an issue in candidates not receiving full marks for the question. Candidates
should be reminded to consider the point value of the question and attempt to provide enough
information. Fully understanding the question and addressing the command terms were also areas of
concern.
Candidates often failed to answer the questions and, on many occasions, just repeated the words in the
stem of the question.
be read in full text view as they were written outside the frame instead of additional pages. The examiners
only see the text box on screen when marking so anything written outside that box may be missed.
The areas of the programme and examination in which candidates appeared well
prepared
In Section A, most candidates were able to recognize the role of error bars and identify independent
variables.
A strong performance was usually shown in questions included on previous exams e.g. recycling of red
blood cells.
Graphs and data in general were interpreted quite well. Many answers requiring just one word were well
answered.
Page 36 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
The strengths and weaknesses of the candidates in the treatment of individual
questions
Most candidates answered Options C and D, followed by Option A. Only a few candidates attempted
Option B.
Section A
Question 1
(a) Some candidates mixed up potatoes and carrots when estimating the isotonic points. Units were often
missing. Many candidates answered 0.2 and 0.4 as they had not drawn a line through the points to
determine the 0% change in mass. The x-axis scale with each division being 0.04 mol dm 3 confused
some students.
(b) Most candidates suggested a reason for the difference in isotonic points.
(c) Most candidates recognised that error bars were included but few expanded their answers to be
awarded 2 points.
(d) The question was poorly phrased, and many candidates did not realise that the question was about
using the % change in mass as opposed to the absolute change. Most candidates got the point for saying
that it shows if water has entered or left the tissue.
Question 2
(a) Most candidates answered temperature as an independent variable.
(b) Most candidates suggested measuring the concentration of the substrate or products. Few gave a
second measurement.
Question 3
(a) and (b) The students who had carried out chromatography experiments performed well though it was
evident that this was unknown material for many. Some centres queried the inclusion of TLC in the
question. The guide states that aper chromatography can be used to separate photosynthetic pigments,
but thin layer chromatography gives better results
advantage of using thin layer chromatography seems reasonable.
(c) A good discriminator. Most candidates scored at least one point for explaining why leaves appear
green. Some candidates did not fully answer this question.
Section B
Option A: Neurobiology and behaviour
Question 4
This question concerning the development of the neural tube in the frog was well answered though quite
a few candidates failed to score 2 marks in (d) referring to development of the whole nervous system.
Question 5
(a) Most candidates were able to identify the structures in the MRI.
Page 37 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(b) The variety of marking points allowed most candidates to get a mark for suggesting how MS had
affected the brain.
(c) Most candidates were awarded 2 3 marks for explaining the folding of the cerebral hemispheres.
Question 6
(a) and (b) Mostly successful, but often the bipolar and ganglion cells were labelled the wrong way
around.
(c) No candidates received full marks for this question. Candidates confuse the left and right visual field
with the left and right eye.
Question 7
Most candidates scored well on this question as it was familiar from previous exams. Many candidates
started their description from the outer ear rather than the inner ear as required.
Option B: Biotechnology and Bioinformatics
Very few candidates attempted this option
Question 8
Most candidates were familiar with the fermenter and the distinction between batch and continuous
culture fermentation.
Question 9
Candidates confused transgenic plants with contamination. Few were able to outline the use of
Agrobacterium in the process.
Question 10
Very few candidates could identify the reading frame.
Question 11
This question was well answered. Candidate could interpret the graph and scored well when answering
about biofilms.
Option C: Ecology and conservation
Question 12
(a) Candidates were able to discern the different trends in the graph.
(b) Most candidates were awarded a mark though there was some confusion about whether the question
referred to transfer within the closed ecosystem or transfer to the outside.
(c) Few candidates received full marks for this question on pyramids of energy. Information was often
repeated in the response.
Question 13
(a) The variety of marking points allowed most candidates to get a mark for explaining keystone species
though some confused keystone species with the predominant species.
Page 38 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
(b) While many candidates were able to contrast the different niches, they did not include the similarities.
Question 14
(a) and (b) Most candidates scored some points in explaining bioaccumulation and describing the use of
indicator species. The top candidates scored full marks.
Question 15
(a) Most candidates were awarded a mark for this question about environmental disturbance as the mark
scheme included most possible responses.
(b) Only a few candidates included the location where the alien species were located. It was interesting to
note the inclusion of some local alien species. Most candidates received full marks for outlining the impact
of alien species.
Option D: Human physiology
Question 16
(a) The question was vague but the mark scheme was written in such a way that almost all candidates
recognised that there was more energy in the faeces, and the better candidates discussed further
implications.
(b) Varied responses given on how to measure energy content by combustion. Those candidates familiar
with the procedure were able to achieve full marks. Many attempted to write the formula but very few did
so correctly.
Question 17
(a) and (b) One-mark questions, they were well answered overall. Many gave incomplete answers in (b)
(ii) by simply stating the adaptation and not outlining the function. The idea that the cells contained
of microvilli.
Question 18
In general, the candidates could explain how materials in the red blood cells are recycled in the liver and
could state a cause of consequence of jaundice.
Question 19
Many candidates could correctly explain the heart sounds. Some candidates incorrectly stated the sound
was caused by the valves opening.
Recommendations and guidance for the teaching of future candidates
Ensure that candidates have seen past examination papers to become familiar with content and structure
in previous exams.
Advise candidates to keep writing neat and within boxes when answering the questions. Candidates must
be to the point. Often, they repeat the question (no marks) and have not enough
space for the answer. Also, they often repeat themselves by using other words (no extra marks).
Page 39 / 40
© International Baccalaureate Organization 2020
November 2019 subject report
Biology
Let candidates know that both Sections A and one option in Section B need to be answered. In addition,
answering all the options does not increase the chance of scoring well.
It is important for candidates to understand the command terms. For example, in a question such as
Compare and contrast fundamental and realized niche of a species
similarities and some for distinctions. It is not possible to score full marks putting only similarities or
distinctions.
Candidates should also be aware of the point count of the question as an indicator of how much detail is
required in an answer.
Section A normally contains straightforward questions to those candidates with practical experience.
Ensure the candidates are familiar with these experiments.
Page 40 / 40
© International Baccalaureate Organization 2020