IB MYP 4-5 Biology Chapter 11 : Evidence–Practice Questions

Question:

Caenorhabditis elegans flatworms start life as a single cell. Adult males have a total of exactly 1,031 cells. Calculate how many cell divisions would have to occur to produce an adult male, if all cells divide at exactly the same time (synchronously).

▶️Answer/Explanation

Ans: 1 → 2 → 4 → 8 → 16 → 32 → 64 → 128 → 256 → 512 → 1024 (almost enough) → 2048 (more than enough); eleven synchronous divisions to produce enough cells.

Question:

The graph shows the number of cells in C. elegans in the first 210 minutes of life. Interpret the data in the graph to answer these questions:

a) Do the cells all divide synchronously?

▶️Answer/Explanation

Ans: Not exactly synchronous; but there are periods when many cells divide.

b) What is the approximate time interval between one cell division and the next?

▶️Answer/Explanation

Ans: Major division periods occur at about 93, 118, 147 and 183 hours after fertilization; the intervals between these periods are 25, 29 and 36 hours so the intervals appear to be getting longer.

Question:

The total number of cells after 210 minutes is 182. Interpret this data and the data in the graph to answer these questions:

a) How many cell divisions would be needed to produce 182 cells?

▶️Answer/Explanation

Ans: Eight synchronous divisions would be needed to produce at least 182 cells.

b) Have all cells completed this number of divisions?

▶️Answer/Explanation

Ans: If all cells had divided in each round of division there would have been 256 cells; so not all cells have completed 8 divisions.

Question:

The pattern of development in C. elegans involves a process called apoptosis (programmed cell death). In hermaphrodites, 131 cells kill themselves by apoptosis. How many cells must be produced by cell division if the final cell total in an adult hermaphrodite is 959?

▶️Answer/Explanation

Ans: 959 + 131 = 1090 cells.

Question:

Describe the relationship between age and telomere length.

▶️Answer/Explanation

Ans: Telomeres become shorter with increasing age; rate of decrease gets less over time.

Question:

Evaluate the claim that telomere length is variable within a population.

▶️Answer/Explanation

Ans: Data in the graph supports the claim; telomeres are shown to vary from more than 10 kb (kilobases) to fewer than 4 kb; length must be variable as it reduces during the lifetime and a population consists of people at different stages in their life; graph shows that at any specific age there is a range in telomere length.

Question:

Suggest some possible causes of shorter telomeres in some individuals.

▶️Answer/Explanation

Ans: Shorter/longer telomere at birth; faster/slower rate of decrease in telomere length per year; variation in rates of cell division; possible environmental influence on the rate of cell division.

Question:

a) List three processes which are dependent on mitosis.

▶️Answer/Explanation

Ans: Body growth; asexual reproduction/cloning; repair/replacement of damaged tissue; growth of tumours.

b) If the ability of the body to carry out processes dependent on mitosis decreased with age, what would be some of the consequences?

▶️Answer/Explanation

Ans: Slower healing after injury; skin becoming thinner; slower/no body growth; slower hair growth; slower/no asexual reproduction; slower growing tumours/cancer.

Question:

1. How many cells are in mitosis?

▶️Answer/Explanation

Ans: Five cells in mitosis.

 

Question:

In what stage of mitosis is each cell?

▶️Answer/Explanation

Ans: Upper left cell: telophase; middle left cell: telophase; middle centre cell: metaphase; lower left cell: anaphase/telophase; lower right cell: prophase.

Question:

How many cells are in interphase? It is easiest to count the number of nuclei and the red blood cells should be ignored.

▶️Answer/Explanation

Ans: 171 cells in interphase (allow a wide range of answers because accurate counting is difficult).

Question:

Calculate the mitotic index of this tumor.

▶️Answer/Explanation

Ans: (5/176) × 100%; = 2.8

Question:

Display the data in whatever graph or chart you consider most appropriate.

▶️Answer/Explanation

Ans: Bar chart; percentage survival on yaxis with scale and legend; six groups on xaxis with clear labels; grouped by tumour size or by mitotic index (two groups of three bars or three groups of two bars).

Question:

a) Is there a positive or negative relationship between the mitotic index and the survival rate after six years? (If there is a positive relationship, then the survival rate is higher if the mitotic index is higher.)

▶️Answer/Explanation

Ans: Negative relationship; the higher the mitotic index the lower the percentage survival.

b) What is the explanation for this correlation?

▶️Answer/Explanation

Ans: Tumour growing faster; secondary tumours will also grow rapidly.

Question:

Is the size of the tumor or the mitotic index a better indicator of the chance of survival?

▶️Answer/Explanation

Ans: Mitotic index is a better indicator; larger differences in survival percentage with variation in mitotic index than with tumour size.

Question:

The women in this trial were all given regular scans of their liver and bones and X-rays of their breasts and liver. What is the reason for these tests?

▶️Answer/Explanation

Ans: To check for secondary tumours; metastasis; to decide whether chemotherapy is needed.

Question:

What are the reasons for some new treatments being very expensive?

▶️Answer/Explanation

Ans: Drug companies want to recoup the cost of developing the treatment; new treatments are under patent so competition cannot drive down the price; new treatments involve antibodies/ proteins that are expensive to produce.

Question:

Is there a limit to how much national health services or health insurance schemes should pay for cancer treatments?

▶️Answer/Explanation

Ans: Yes, because limits force drug companies to restrict prices; limits make it possible for a treatment to be made available to everyone/more patients; money for health care is limited so without price limits for cancer therapy other treatments will be restricted; costbenefit analyses may show that the extra days/months of life are not warranted if the costs of treatment are very high.

Question:

Should individuals or families be allowed to pay for expensive treatments that only have a small chance of extending life significantly?

▶️Answer/Explanation

Ans: Difficult to make it illegal to spend money on relatives’ health care; doctors should give guidance about whether the money will provide enough painfree rewarding days of life to the relative; perhaps not ethical for the very wealthy to monopolize resources/health care professionals’ time if others then do not receive adequate care; treatment providers should be regulated so to be prevented from making promises of recovery that are not justified by evidence.

Question:

Explain how each of the following can cause cancer:

a) nuclear bombs

▶️Answer/Explanation

Ans: Nuclear bombs release radioactive fallout; beta particles/gamma rays; radiation causes mutations; in oncogenes.

b) artificial sunbeds

▶️Answer/Explanation

Ans: Sunbeds emit UV radiation; UVA and UVB; causes mutations in skin cells; causes skin cancer.

c) smoking

▶️Answer/Explanation

Ans: Chemical mutagens in cigarette smoke; more than 30 chemicals shown to be mutagenic; cause chemical changes in DNA; cancer if mutations are in oncogenes.

d) X-rays.

▶️Answer/Explanation

Ans: Xrays are high energy/ionizing radiation; cause mutations.

Question:

Debate whether each of the four causes in question 1 should be made illegal because they increase the risk of cancer.

▶️Answer/Explanation

Ans: Depends on the risk of cancer that they cause; and any benefits their use brings; there are ethical questions over whether it is right to prevent an individual from causing harm to themselves;
additional issues arise in jurisdictions where there is publicly funded health care.

Question:

Outline the distribution of particulate air pollution globally.

▶️Answer/Explanation

Ans: Highest pollution levels in India/China/Middle East; high levels in cities; higher levels in developing countries/lower levels in developed countries.

Question:

Predict the pattern of the global distribution of respiratory diseases such as asthma, emphysema and lung cancer.

▶️Answer/Explanation

Ans: Positive correlation with levels of air pollution; the higher the level of air pollution the higher the incidence of asthma/emphysema/lung cancer/ respiratory diseases; not directly proportional
because other factors influence these diseases.

Question:

Using only the data in the graph, identify the relationship between mortality due to lung cancer and lichen biodiversity in the Veneto region.

▶️Answer/Explanation

Ans: Negative correlation; lower lichen biodiversity with higher lung cancer mortality.

Question:

Explain the relationship between mortality due to lung cancer and lichen biodiversity.

▶️Answer/Explanation

Ans: Lung cancer isn’t caused by low lichen biodiversity; lung cancer mortality is positively correlated with concentration of air pollutants; lichen biodiversity is negatively correlated with concentration of air pollutants; so there is a negative correlation between concentration of air pollutants and lung cancer mortality.

Only men who had lived in one region for their entire life were included in the investigation.

Question:

Suggest one reason for excluding other men.

▶️Answer/Explanation

Ans: They might previously have lived in an area with a different concentration of the air pollutants that cause cancer; lung cancer takes a long time to develop and be diagnosed.

Question:

Suggest two reasons for the points on the graph not all lying on the line of best fit.

▶️Answer/Explanation

Ans: Other factors affect lung cancer mortality; other factors affect lichen biodiversity.

Question:

What does the data given here suggest about the relationship between the species in the table?

▶️Answer/Explanation

Ans: Differences in base sequence:
Adoxophyes honmai to Diatraea saccharalis 41

Adoxophyes honmai to Ostrinia furnacalis 6

Adoxophyes honmai to Ostrinia nubilalis 13

Diatraea saccharalis to Ostrinia furnacalis 35

Diatraea saccharalis to Ostrinia nubilalis 38

Ostrinia furnacalis to Ostrinia nubilalis 17

So Diatraea honmai is most dissimilar in base sequence to the other three species; and is not closely related to any of them; the other three species are closely related to each other; as they have many similarities in base sequence.

Question:

Based on the table, which two species are the most closely related?

▶️Answer/Explanation

Ans: Adoxophyes honmai and Ostrinia furnacalis are most similar; Adoxophyes honmai is more similar to both Ostrinia species despite them being in the same genus.

Question:

Robert Koch hypothesized that anthrax was caused by the presence of rod-shaped bacteria that he observed in the blood of infected cows. Explain how Koch could apply the method above using infected cows, mice, a culture tube and a microscope to confirm his hypothesis.

▶️Answer/Explanation

Ans: Take blood sample from an infected and an uninfected cow; view the blood samples under a microscope to confirm the presence of anthrax bacteria in the sample from the infected but not from the uninfected cow; culture the pathogen in a tube; inoculate a healthy mouse with anthrax bacteria from the culture; confirm that the mouse develops the disease; take a blood sample from the diseased mouse; view the blood samples under a microscope to confirm the presence of anthrax bacteria in the sample; culture the pathogen in a tube.

Question:

Discuss some possible limitations to Koch’s postulates in identifying the cause of a disease.

▶️Answer/Explanation

Ans: Mice may not contract the disease because the pathogens are not adapted to them/because the mice already have immunity; death might be caused by other factors from the disease they are infected with.

Question:

For which types of disease would Koch’s postulates not be helpful?

▶️Answer/Explanation

Ans: Viral diseases because they cannot be cultured on acellular media; genetic/degenerative/mental diseases.

Question: 

What are the limitations of animal models?

▶️Answer/Explanation

Ans: Differences between animals; in physiology/metabolism/anatomy/immune system; so findings in the model animal may not apply to other animal species.

Question:

Discuss the ethical considerations of the third postulate.

▶️Answer/Explanation

Ans: Possibly unethical to inoculate a healthy mouse/animal with a pathogen; causes suffering/could kill a healthy animal.

Question: 

Suggest reasons for doctors advocating triple rather than single vaccines.

▶️Answer/Explanation

Ans: Children don’t like vaccinations so the fewer the better; cheaper to do one vaccination than three separate ones; more likely that a child will be fully vaccinated against the three diseases.

The MMR vaccination is optional in the UK. The data in the top graph shows the percentage of children vaccinated (MMR uptake) over a 13-year period.

Question:

Outline the pattern of MMR uptake over the period shown in the graph.

▶️Answer/Explanation

Ans: Increased between 199091 and 9293; remained high (from 9293 to 9697); decreased (after 1998); decreased steeply (after 2000).

Question:

Suggest, giving a reason, a year in which the UK media may have carried a story about research making a link between MMR and autism.

▶️Answer/Explanation

Ans: Somewhere in the range of 19961999.

Question: 

Outline the trend in the incidence of autism over the period shown in the graph.

▶️Answer/Explanation

Ans: Incidence of autism increased; increased from 88 to 90 and from 92 to 94; decreased from 90 to 91/94 to 95.

Question: 

Evaluate using the data the claim that autism is linked to the MMR vaccine.

▶️Answer/Explanation

Ans: Claim not supported by the data; MMR vaccination rate dropped from over 70% to nearly 0% in 1992; yet there was a larger increase in diagnosis of autism after that time; no sign of drop in autism even four years later.

Question:

Using the data in the graph, explain the changes in rates of whooping cough in the 50 years from 1940 to 1990.

▶️Answer/Explanation

Ans: Number of cases was high and fluctuating before the use of DTP; cases dropped from over 300 per 100,000 to below 50 after the introduction of the vaccine; cases rose when the vaccine uptake dropped from 81% to 31%; but cases decreased again when vaccine uptake rose back to 93%; clear link between vaccine uptake and cases of whooping cough.

Summative assessment

The causes of disease

Question:

a) Outline an example of a disease that has:

i) an environmental cause 

▶️Answer/Explanation

Ans: Asbestosis/Minamata disease.

ii) a pathogen-based cause 

▶️Answer/Explanation

Ans: Influenza/malaria/syphilis/Athlete’s foot.

iii) a lifestyle cause. 

▶️Answer/Explanation

Ans: Obesity/anorexia nervosa.

Question:

A human life starts with a single cell that follows a precise controlled pattern of cell divisions leading to the development of an embryo, then a fetus and eventually an adult. The pattern of cell divisions has been studied in simple organisms, such as the flatworm Caenorhabditis elegans. In a study, an embryo of C. elegans was treated with fluorescent stains, so nuclei appear blue and
mitochondria green. Other cell structures are not visible.

a) What is the overall shape of the embryo at this stage? 

▶️Answer/Explanation

Ans: Spherical.

b) Estimate the total number of cells in the embryo. How reliable is your estimate?

▶️Answer/Explanation

Ans: About 50 nuclei visible; but some are concealed behind others so this is an underestimate; overall estimate is about 60/ is 50 70; not very reliable.

c) If the embryo contained 64 cells, how many rounds of cell division would there have been up to this stage?

▶️Answer/Explanation

Ans: 1 → 2 → 4 → 8 → 16 → 32 → 64; so 64 cells are produced by six rounds of division.

d) What process is used to divide one nucleus into two genetically identical nuclei?

▶️Answer/Explanation

Ans: Mitosis.

e) Do the cells of the embryo each contain more nuclei or more mitochondria?

▶️Answer/Explanation

Ans: More mitochondria.

f) Like whole cells, mitochondria can only be produced by division of pre-existing mitochondria. What would be the consequence if the mitochondria in the embryo divided at a slower rate than the embryo cells?

▶️Answer/Explanation

Ans: Some cells would have no mitochondria; could not carry out aerobic respiration; would have no/too little energy for cell processes; would die.

Analyzing data related to coronary heart disease, cancer and childhood mortality

Increasing age, gender and family history are factors which are outside of an individual’s control, unlike smoking, high blood pressure and bad dietary choices, all of which are risk factors for declining health.

Question:

In the late 1960s, Finland had the highest death rate from coronary heart disease in the world, with working-age men in the eastern part of the country carrying the highest risk of CHD. To help
decrease deaths from CHD, a community-based project was set up, with the aim of reducing the levels of the three main cardiovascular risk factors: dietary cholesterol, smoking and high blood pressure.
Between 1972 and 2012, a study was conducted to determine whether the measures taken in the community project were efficient. Over 34,000 men and women, aged 30–59 at the beginning of the study and living in eastern Finland, participated.
The data in the graphs below shows the reduction in death rates as well as changes in the prevalence of the risk factors, in both men and women (1972 is set as the 100% level for each of the variables observed).

a) Estimate the reduction in actual CHD mortality between 1972 and 2012 in men.

▶️Answer/Explanation

Ans: Reduced to 18% of the level in 1972 = 82% reduction.

b) Identify which risk factor changed most significantly in men.

▶️Answer/Explanation

Ans: Blood cholesterol decreased most.

c) Distinguish between the changes in smoking in men and women over the course of the study.

▶️Answer/Explanation

Ans: More smoking in women but less in men.

d) i) Distinguish between the actual reductions in deaths due to CHD and the predictions.

▶️Answer/Explanation

Ans: Actual reductions greater than the predictions; reduction to about 18% compared with prediction of about 44% in both men and women.

ii) Suggest reasons for the difference.

▶️Answer/Explanation

Ans: Factors that influence the incidence of CHD other than smoking, blood pressure and cholesterol had improved during the study period; better treatment for CHD lowered its incidence.

Question: 

The bar chart shows ten cancers with the highest mortality rates globally. The mortality rate is the number of deaths per year in 100,000 people. Lung cancer has been split into deaths in smokers
and in people who have never smoked.

a) Calculate how much greater the chance of lung cancer is in smokers compared to non-smokers.

▶️Answer/Explanation

Ans: The increased chance is 8.8 3.1 = 5.7 more deaths per 100,000.

b) i) Deaths due to lung cancer in non-smokers would drop if nobody smoked. Explain this paradox.

▶️Answer/Explanation

Ans: Passive smoking; nonsmokers inhale in smoke exhaled by smokers; containing carcinogens/mutagens; in places where nonsmokers and smokers are together.

ii) Suggest changes to the environment, apart from stopping cigarette smoking, which would reduce deaths due to lung cancer. 

▶️Answer/Explanation

Ans: Prevent air pollution caused by burning coal; ban diesel vehicles from cities/eliminate NOX from air that humans breathe; remove asbestos; wear face masks if there is a danger of inhaling silica/ rock dust/nickel/arsenic/cadmium; remove radon gas from homes/buildings.

c) In research involving 174 patients with lung cancer in Japan, the time taken for a lung tumor to double in size was found to be very variable, ranging from 30 to 1,077 days. Discuss the consequences of the doubling rate of a tumor for the patient.

▶️Answer/Explanation

Ans: With slow doubling rate there is likely to be a longer time before a tumour is discovered because of its effects; with slow doubling rate there is more chance of discovering a tumour before it becomes large by routine screening programs; with slow doubling rate there is less chance of secondary tumours causing rapid death; with slow doubling rate there is less chance of  hemotherapy working (because a smaller proportion of cells is in mitosis and therefore vulnerable to chemotherapy drugs).

Question:

Gapminder (www.gapminder.org) is website that makes a wider variety of data available for exploration, including data related to global health issues.
One of the United Nations’ 17 “Sustainable Development Goals” refers to good health and well-being. This goal includes the target of reducing under-5 mortality from such infectious diseases as
diarrhea, HIV, malaria, measles, pertussis, pneumonia, as well as reducing deaths due to accidents.
The data shown in the graph represents the trend in under-5 mortality in four countries since 1800, as investigated on Gapminder.

a) State the under-5 mortality rate in Australia in 1800. 

▶️Answer/Explanation

Ans: 390 deaths per 1,000.

b) Compare and contrast the trends in under-5 mortality in the four countries.

▶️Answer/Explanation

Ans: Overall decrease in child mortality in all countries; all countries reach mortality below 50 by the end of the study period; mortality in Chile and Bangladesh rises during the middle of the study period to a level higher than at the start before falling again whereas it never rises above the initial level in Australia or Azerbaijan; decrease in mortality starts earlier in Australia.

c) Suggest reasons for the observed patterns. 

▶️Answer/Explanation

Ans: Decreases are due to improvements in medicine; such as vaccinations; and public health measures/clean water; and better nutrition; earlier decrease in Australia because these measures were introduced sooner.

d) The Sustainable Development Goal target for 2030 is to reduce under-5 mortality to 25 per 1,000 in all countries. Use the database to find three countries that have reached that target currently and four countries that have yet to reach that target.

▶️Answer/Explanation

Ans: Answers will depend on when the database is consulted.

Question:

Explore the other data sets available on Gapminder and develop a question to explore regarding how health indicators have changed with time.

a) Clearly state your question.

▶️Answer/Explanation

Ans: Compare and contrast changes in the incidence of malaria in two different geographic regions.

b) Choose representative countries for your study and provide a justification for this choice.

▶️Answer/Explanation

Ans: For example compare equatorial Africa with Southern Africa: Congo, CAF and Gabon versus Zambia, Mozambique and Zimbabwe.

c) Produce graphs using the trails functionality on Gapminder.

▶️Answer/Explanation

Ans:

d) Analyze your graphs and state your conclusions.

▶️Answer/Explanation

Ans: Pattern is variable though the highest rates are seen in Southern Africa from 1999; the rates are very high at 40,000/100,000 in Zambia.

Consequences of smoking during pregnancy

Question:

The text that follows consists of two extracts from “Molecular Epidemiology: On the Path to Prevention?” by FP Perera in the Journal of the National Cancer Institute (2000, Vol 92, pp 602–612).

a) Explain what is meant by:

i) carcinogen 

▶️Answer/Explanation

Ans: A chemical substance or form of radiation that causes cancer to develop.

ii) in utero 

▶️Answer/Explanation

Ans: In the uterus/before a baby has been born.

iii) cell proliferation. 

▶️Answer/Explanation

Ans: Division of cells to produce many.

b) The text is written in scientific language that non-scientists may find difficult to understand. Write a short and easily comprehensible article to explain to women who have just become pregnant why it would be wrong for them to smoke.

▶️Answer/Explanation

Ans: Award marks on a scale from 0 for an article that is without merit because it is misleading, inaccurate or incomprehensible up to 8 marks for a succinct article that presents all the information needed to convince pregnant women that they should not smoke, written in an engaging and comprehensible style.

c) List other pieces of health advice that you would give to pregnant women based on the text extracts.

▶️Answer/Explanation

Ans: Avoid inhaling vehicle exhaust fumes/emissions from power plants/fumes from industry; avoid inhaling fumes from fires/stoves/heaters used in the home; avoid smoked/grilled food/ avoid all sources of radiation.

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