Genetic diversity

Crab blood contains the respiratory pigment haemocyanin.

Figure 3 shows the dissociation curve for oxyhaemocyanin in a species of crab at two temperatures.

Crabs use gills for gas exchange.

Use Figure 3 to explain how the increase in temperature affects the ability of haemocyanin to load or unload oxygen at the gills and in tissues.

Refer to high pO₂ and low pO₂ in your answer.

Figure 4 shows the colour of haemocyanin with increasing concentrations of oxygen.

A calibration curve can be used to determine the percentage oxygen saturation of haemocyanin in a sample of crab blood.

You are given samples of crab blood in which the percentage oxygen saturation of haemocyanin is known.

Use all the information provided to:

describe how you could produce a calibration curve for the percentage oxygen saturation of haemocyanin in crab blood

identify one control variable used in the procedure to obtain data for the calibration curve.

One control variable

Ghost crabs live on sandy beaches.

Ghost crabs can run for a long time before they get tired and have to stop.

A scientist calculated the mean time ghost crabs could run for at different speeds before they stopped.

Figure 5 summarises the scientist’s results.

A ghost crab running at 0.14 m s^–1 covered a distance of 504 m in 1 hour.

Use Figure 5 to calculate the extra distance this crab could cover if it continued running at 0.14 m s^–1 before it stopped running.

Show your working.

Figure 6 shows the data points from individual crabs that were used to plot the curve in Figure 5.

Figure 6

Figure 6 not reproduced here due to third-party copyright restrictions.

The figure is adapted from Figure 1 in https://journals.co.za/doi/pdf/10.10520/AJA00445096_586

The scientist selected the crabs at random from one sandy beach. Before the investigation, the crabs were equally rested and fed identical diets.

Use information in Figure 6 to suggest why the line of best fit in Figure 5 is not a good indicator of the time ghost crabs can run for.

Define the biological term population.

Ecologists monitored the biodiversity of birds in a protected woodland.

They recorded the number of bird species breeding in the woodland on the same day, every year for a 30-year period.

Figure 4 shows their results.

Figure 4

Figure 4 not reproduced here due to third-party copyright restrictions

The figure is taken from the following website:

Figure 1a. Anne E. Magurran, Stephen R. Baillie, Stephen T. Buckland, Jan McP. Dick, David A. Elston, E. Marian Scott, Rognvald I. Smith, Paul J. Somerfield, Allan D. Watt, Long-term datasets in biodiversity research and monitoring: assessing change in ecological communities through time, Trends in Ecology & Evolution, Volume 25, Issue 10, 2010, Pages 574-582, ISSN 0169-5347, https://doi.org/10.1016/j.tree.2010.06.016.

Which statement correctly represents the species richness of the woodland?

Tick () one box.

A student studying the information in this question concluded that all woodlands should be protected to increase the biodiversity of birds.

Evaluate the student’s conclusion.

It is not possible to extrapolate the data for the number of bird species recorded breeding each year beyond 1979.

Explain why.

In this woodland, the ecologists measured the similarity in the bird community by comparing each year to 1949 using an index of similarity.

This index ranges from 1.0 for total similarity to 0.0 for total dissimilarity.

Figure 5 shows their results.

Figure 5

Figure 5 not reproduced here due to third-party copyright restrictions

The figure is taken from the following website:

Figure 1b, Anne E. Magurran, Stephen R. Baillie, Stephen T. Buckland, Jan McP. Dick, David A. Elston, E. Marian Scott, Rognvald I. Smith, Paul J. Somerfield, Allan D. Watt, Long-term datasets in biodiversity research and monitoring: assessing change in ecological communities through time, Trends in Ecology & Evolution, Volume 25, Issue 10, 2010, Pages 574-582, ISSN 0169-5347, https://doi.org/10.1016/j.tree.2010.06.016.

Suggest how the changes in the index of similarity in the bird community provide evidence for the process of succession.

In Figure 5, the index of similarity for the last 10 years remains fairly constant.

Name the stage of a succession this represents.

Suggest one reason why the index of similarity is not absolutely constant.

The Living Planet Index (LPI) is an index designed to monitor the state of the world’s biodiversity.

The LPI is arbitrarily scaled to be 1.0 in 1970, the baseline year.

Figure 6 shows the LPI from the Living Planet Report, 2008. The dotted lines represent ± 2 standard deviations from the mean, which includes over 95% of the data.

Figure 7 shows an alternative version of Figure 6 published on a news website.

Figure 6 Figure 7

Figures 6 and 7 not reproduced here due to third-party copyright restrictions

The figures are taken from the following website:

Figure 2a and 2b, Anne E. Magurran, Stephen R. Baillie, Stephen T. Buckland, Jan McP. Dick, David A. Elston, E. Marian Scott, Rognvald I. Smith, Paul J. Somerfield, Allan D. Watt, Long-term datasets in biodiversity research and monitoring: assessing change in ecological communities through time, Trends in Ecology & Evolution, Volume 25, Issue 10, 2010, Pages 574-582, ISSN 0169-5347, https://doi.org/10.1016/j.tree.2010.06.016.

The news website published the headline:

The LPI shows human activities cause significant decrease in biodiversity.

Suggest three reasons why this headline is not valid.

Use all the information provided.

Turn over for Section B

Section B

one question.

You are advised to spend no more than 45 minutes on this section.

A student investigated the use of cinnamon oil as an antimicrobial substance. She investigated the effect of cinnamon oil on the growth of five different bacterial cultures grown on agar plates.

The student added 100 mm³ of each bacterial culture from its glass bottle onto a separate agar plate. She spread each bacterial culture evenly over the agar using a spreader.

Describe the aseptic techniques she should use.

On each agar plate, the student cut a well (a hole) in the agar.

The well had a diameter of 6 mm. The student added 50 mm³ of cinnamon oil into the well.

Calculate the minimum depth of the well to allow the addition of 50 mm³ of cinnamon oil. Use the following equation in your calculation:

Use 3.14 as the value for π.

Show your working.

The student kept the plates at 25 °C for 24 hours.

Figure 5 shows what one of her plates looked like after 24 hours.

The student measured the diameter of the clear zone with no bacterial growth around each well. She made these measurements to the nearest whole mm

Table 1 shows her results.

Suggest exactly what the student added to the wells to get the positive control and negative control results.

Complete Table 1 to show the median and mean diameters.

The mean ± 2 standard deviations includes over 95% of the data.

Use this information to consider whether the standard deviations suggest the differences in means are likely to be due to chance.

Explain your answer, including at least one calculation.

Give two types of cell that can stimulate an immune response.

An autoimmune disease causes the immune system to attack healthy body tissues. Scientists investigated the immune responses of healthy mice and mice with autoimmune disease.

The chemical OXA causes an immune response in mice and can make their skin swell. Mice had olive oil applied to their left ear and OXA in olive oil applied to their right ear.

The immune response was recorded in two ways:

• the cellular response by measuring the mean increase in ear thickness 24 hours after exposure to OXA

• the humoral response by measuring the mean concentration of anti-OXA antibody in blood 14 days after exposure to OXA.

Table 2 shows the results of this investigation. The values in the brackets show ± 2 standard deviations. A value of ± 2 standard deviations from the mean includes over 95% of the data.

Suggest and explain one reason why olive oil was applied to the left ear of the mice.

Plot a suitable graph for mean increase in ear thickness for each group of mice in Table 2.

Include the data for ± 2 standard deviations on your graph.

What can you conclude about the effects of autoimmune disease on the cellular response and the humoral response in male and female mice?

Use the data to justify your conclusions.

Some studies have shown that in humans, oestrogen has the opposite effect on two different autoimmune diseases. Oestrogen:

• accelerates the progression of systemic lupus erythematosus (SLE)

• prevents the progression of rheumatoid arthritis (RA).

The scientists investigated the effect of oestrogen on the immune response in healthy mice and mice with autoimmune disease.

Table 3 shows the scientists’ results.

A student studying these data made the following conclusions.

1. In humans, SLE is caused by an overproduction of antibodies.

2. In humans, RA is caused by an overproduction of cytotoxic T cells (T_C cells).

Evaluate the student’s conclusions.

In mice, one type of autoimmune disease is inherited as a dominant allele. Would the Hardy–Weinberg principle hold true for a population of mice, some of which had this autoimmune disease?

Explain your answer.

Describe how a triglyceride molecule is formed.

Table 5 shows some properties of four fatty acids.

Figure 10 shows diagrams of these fatty acids.

Put a tick () in one box that contains correct information about one of these fatty acids.

The percentage of saturated fatty acids compared with unsaturated fatty acids found in lipid stores in seeds differs in different populations.

Scientists investigated two populations of the plant, Helianthus annuus.

The scientists grew young plants from seeds collected from each population. They placed the seeds on wet tissue paper so that the root growth was visible.

They grew seeds from each population at two temperatures:

• warm temperature of 24 °C

• cool temperature of 10 °C

After 10 days, the scientists measured the length of each root.

Table 6 shows some of the properties of the two populations and the scientists’ results.

The mean ±2 × standard deviation includes 95% of the data.

The scientists used a data logger to measure the length of the root rather than a ruler.

Suggest one reason why they used a data logger and explain why this was important in this investigation.

It is known that:

• during respiration saturated fatty acids yield more energy than unsaturated fatty acids

• saturated fatty acids have higher melting points than unsaturated fatty acids

• lipases in seeds act more rapidly on liquid substrates.

Use this information and Table 6 to show how each population is better adapted for its natural environment when compared with the other population.

Although these two populations are completely separate and show genetic variation, they are both called Helianthus annuus.

Explain why they are both given this name.

Complete Table 2 to show three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Scientists investigated the genetic diversity between several species of sweet potato. They studied non-coding multiple repeats of base sequences.

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.

The percentage similarities in the non-coding multiple repeats of base sequences of four species of sweet potato are shown in Table 3.

Use the information in Table 3 to complete the phylogenetic tree shown in Figure 8.

Write the letter that represents the correct species into each box.

The scientists studied five individuals from each species. Within the five individuals of species T they found a percentage similarity of 66%.

Use Table 3 to evaluate how this information affects the validity of the phylogenetic tree.

Uncontrolled cell division can cause tumours to form.

Figure 7 shows the growth pattern followed by a type of tumour.

Use Figure 7 to calculate the percentage of maximum growth this type of tumour reaches before it can be detected.

You will need to use the 10^x button on your calculator.

Figure 7 can also be used to calculate the age of this type of tumour.

At diagnosis, a patient had a tumour of 3.98 10¹¹ cells. Calculate the age of the tumour.

You will need to use the log₁₀ button on your calculator.

Trexall is a drug that can be used to slow the development of various forms of cancer.

Trexall slows cell division by interacting with an enzyme called dihydrofolate reductase (DR).

DR is involved in making nucleotides; the substrate for DR is folic acid.

Figure 8 shows the chemical structure of Trexall.

Figure 9 shows the chemical structure of folic acid.

Use the information provided to suggest how Trexall slows cell division.

Doctors investigated how the concentration of Trexall given to patients affected the growth of lung tumours. The doctors measured the volume of tumours at the beginning of the study and after 8 months.

Figure 10 shows the results of this investigation. The bars represent ± 2 standard deviations. A value of ± 2 standard deviations from the mean includes over 95% of the data.

The scientists measured the percentage change in tumour volume.

Suggest why they recorded both percentage change and tumour volume.

Percentage change

A lung cancer patient received 15 mg of Trexall per week. After treatment, the diameter of his lung tumour was 35.8 mm

Assuming the tumour was spherical, use the mean percentage change in tumour volume shown in Figure 10 to calculate the volume of the patient’s tumour before treatment with Trexall.

The formula for the volume of a sphere is πr³ where π = 3.14

To reduce the size of tumours, would it be better to use 30 mg of Trexall per week, or 20 mg of Trexall per week?

Explain your answer.

Trexall can also be used to slow the development of rheumatoid arthritis (a pain-causing joint disease).

Scientists investigated the effectiveness of Trexall as a pain relief treatment in 12 rheumatoid arthritis patients. All of the patients were female. They randomly divided the patients into two groups:

• Group R received Trexall tablets for 35 days

• Group S was a control group.

They asked both groups to rate their pain on a scale of 0–10 (0 being no pain and 10 being the worst pain possible) at the start and then every 7 days for 35 days. They calculated mean scores for each group.

Their results can be seen in Table 3.

Apart from age and general health, give two important factors when choosing patients for this investigation.

A student analysed Table 3 and concluded that Trexall was effective in reducing pain in arthritis patients.

Evaluate the student’s conclusion.

Turn over for Section B

Section B

one question.

You are advised to spend no more than 45 minutes on this section.

Figure 3 shows two different ways of classifying the same three species of snake.

Classification X is based on the frequency of observable characteristics

Classification Y is based on other comparisons of genetic characteristics.

All three species of snake belong to the Python family.

What do these classifications suggest about the evolutionary relationships between these species of snake?

Complete Table 4 below to show the missing names of the taxa when classifying these snakes.

There is a debate about the name of one of these species of snake. Some scientists name it Liasis papuana and other scientists name it Apodora papuana.

Give the name of the taxon about which the scientists disagree.

State three comparisons of genetic diversity that the scientists used in order to generate Classification Y.

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

Figure 6 shows an image from an optical microscope of meiosis occurring in a flower bud of a flowering plant. W and Z are undergoing meiosis.

Explain the appearance of W and Z.

An environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree.

He was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.

Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees.