The heart & circulation

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.

Describe the roles of ribosomes, tRNA and ATP in the process of translation.

Describe and explain the adaptations of leaves that maximise gas exchange.

Do not refer to organelles in your answer.

Describe the pathway taken by blood between a kidney and the coronary arteries.

Include names of the major blood vessels (arteries and veins) and heart valves involved.

Give two structural features of an aorta wall and explain how they are related to the function of an aorta.

Small tears may occur in the layers of tissue in an aorta wall. These tears weaken the wall without bursting the aorta.

Scientists:

• measured the aorta diameter (d) in a large population of people over 60 years of age

• calculated the risk of an aorta wall developing a tear.

Table 4 shows their results.

Blood may push through the tears in the aorta wall. This produces a balloon-like swelling called an aneurysm and increases the aorta diameter. Aneurysms can cause the aorta to burst.

Using all the information, what can you conclude about aorta diameter and the risk of developing an aneurysm?

A scientist investigated changes in a diseased heart and changes in a healthy heart during cardiac cycles.

For each heart, the scientist obtained a value for:

• the mean blood volume in a full ventricle just before the ventricle contracts (BVB)

• the mean ejection fraction (EF).

The EF is the proportion of blood pumped out of a full ventricle in one heartbeat.

The EF is calculated using this formula:

Table 5 shows the scientist’s results.

Using Table 5, a student calculated that the percentage change in the stroke volume of the diseased heart compared with the stroke volume of a healthy heart is –30%.

The student’s answer is wrong because the final step of the calculation was performed incorrectly.

Using the equation and Table 5, calculate the correct percentage change in the stroke volume of the diseased heart compared with the stroke volume of the healthy heart.

Identify the mathematical error in the final step of the student’s calculation.

Mathematical error

Write an essay on one of the topics below.

Either

Phosphorus-containing substances and their importance in biological systems.

Or

The mechanisms and importance of transport within organisms.

Carbon monoxide (CO) is released during incomplete combustion of fossil fuels.

Figure 7 shows the dissociation curve for oxyhaemoglobin when:

• not exposed to CO

• exposed to CO such that 50% of the oxygen binding sites are occupied by CO (50% COHb).

Using Figure 7, what can you conclude about how exposure to CO affects the loading and unloading of oxygen by haemoglobin?

Explain your answer.

The World Health Organisation (WHO) suggests that to avoid long-term health effects, COHb concentrations should be kept below 2.5%.

WHO recommends that people should not be exposed to:

• air with > 10 mg m^–3 CO for more than 8 hours

• air with > 30 mg m^–3 CO for more than 1 hour.

Scientists have used a mathematical model to calculate the exposure to carbon monoxide that would result in 2.5% COHb in both adults and children.

Table 2 shows the scientists’ results.

The scientists suggest that the WHO recommendations for carbon monoxide concentrations resulting in 2.5% COHb should be reduced.

Evaluate the scientists’ conclusion.

Dengue fever is a human disease caused by the dengue virus.

Scientists designed an ELISA test to detect antibodies to the dengue virus in a patient’s blood sample.

Figure 10 shows a diagram of this test and some information about how it works.

Figure 11 shows the negative and positive results that were produced 20 minutes after the use of the test shown in Figure 10.

Suggest what is on the test at line T and explain what causes the line to appear in a positive test.

A line at C shows that the test has worked.

Suggest one reason why a line at C shows the test has worked.

Figure 12 shows a flowchart of how the anti-human antibodies with enzyme attached are produced.

Suggest why the fused cells allow continuous production of monoclonal antibodies.

Evaluate the ethics of the production process shown in Figure 12.

Early identification of dengue fever can be difficult as many other diseases produce

the same symptoms. Early identification is important because people suffering with dengue fever can become ill very quickly and may need hospital treatment.

Scientists compared the effectiveness of three diagnostic tests for dengue fever.

• Laboratory-based test – a patient’s blood sample is sent from the doctor’s clinic to a laboratory for testing.

• Current test used in the doctor’s clinic.

• New test to be used in the doctor’s clinic – the ELISA test shown in Figures 10 and 11 (on page 24).

The scientists’ results are shown in Table 3.

A blood sample from each patient with confirmed dengue fever at each time after onset of symptoms was tested with all three diagnostic tests.

The scientists recommend that the new test is used for the identification of dengue fever in all countries around the world.

Discuss this recommendation. Use all the information given.

The dengue virus causes damage to capillaries so that blood proteins move out of the capillaries into the tissue fluid.

Explain how this would affect the return of tissue fluid into the capillaries.

Figure 11 shows images of gills from two fish as seen through an optical microscope.

Image C shows gills from a fish with healthy gills.

Image D shows gills from a fish with damaged gills.

Figure 11

Figure 11 not reproduced here due to third-party copyright restrictions

To observe the fish gills with the optical microscope, the scientists used two different stains. The first stain binds to DNA; the second stain binds to the red blood cells.

Explain why a second stain would be needed to stain the red blood cells. Suggest which molecule the stain could bind to in the red blood cells.

Using Figure 11, the scientists calculated the surface area to volume ratios for each gill filament in these two fish. Some of their results are shown in Table 4.

Complete Table 4. State your calculated volume and surface area:volume ratio to 2 significant figures.

The damage to the gills causes uncontrolled cell division in the cells around the capillaries in the gill filaments.

Other than surface area:volume ratio, describe one way this uncontrolled cell division changes the gills, as shown in Figure 11.

Explain how this difference would affect gas exchange.

Figure 12 shows the general pattern of blood circulation in fish.

Use Figure 12 to complete Table 5 to show two differences between the circulation of blood in fish and the circulation of blood in a mammal.

Amino acids are used to make proteins. Table 1 shows the R groups of six different amino acids.

Use Table 1 to identify the three different amino acids used to make the polypeptide shown in Figure 1.

Middle amino acid

Table 2 shows three statements and names of four biological molecules.

Put a tick () in each box where the statement is true for the biological molecule.

Figure 2 represents the structure of adult human haemoglobin.

The number of amino acids in the beta chains in Figure 2 is 3.546% greater than in the alpha chains. Each alpha chain contains 141 amino acids.

Calculate how many amino acids there are in total in the haemoglobin molecule shown in Figure 2. Give your answer to the nearest whole number.

When a substance called BPG binds to haemoglobin, it reduces the affinity of haemoglobin for oxygen.

Figure 3 shows an oxyhaemoglobin dissociation curve for haemoglobin in normal conditions.

Sketch a curve on Figure 3 to show the oxyhaemoglobin dissociation curve for haemoglobin when BPG binds to it.

Suggest and explain when it would be an advantage to a human for BPG to bind to haemoglobin.

A student dissected an organ from a mammal to observe blood vessels.

He dissected a slice of the organ and identified two blood vessels.

Figure 4 shows a photograph of his dissection.

Figure 5 shows a drawing of the blood vessels from his dissection.

Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection.

Identify the type of blood vessel labelled as X and the type of blood vessel labelled as Y in Figure 4.

Describe one feature that allowed you to identify the blood vessels.

Describe two precautions the student should take when clearing away after the dissection.

Figure 3 shows pressure and blood flow during the cardiac cycle in a dog.

At P on Figure 3, the pressure in the left ventricle is increasing. At this time, the rate of blood flow has not yet started to increase in the aorta.

Use evidence from Figure 3 to explain why.

At Q on Figure 3 there is a small increase in pressure and in rate of blood flow in the aorta.

Explain how this happens and its importance.

A student correctly plotted the right ventricle pressure on the same grid as the left ventricle pressure in Figure 3.

Describe one way in which the student’s curve would be similar to and one way it would be different from the curve shown in Figure 3.

Use information from Figure 3 to calculate the heart rate of this dog.

Table 2 shows information about two types of medicine.

A journalist studied the data in Table 2. She made the following suggestion.

‘If an adult takes the maximum number of tablets allowed for either of the medicines, then the person would have more than the RDA of sodium.’

The RDA (recommended daily allowance) of sodium for an adult human is 2.4 g per day.

Is the journalist’s statement true for both of the medicines in Table 2 ?

Use suitable calculations to support your answer.

Show your working.

Doctors investigated the link between high sodium concentrations in medicines and hypertension (high blood pressure).

They analysed medical records of patients. 1 292 337 of these patients had taken medicines containing high sodium concentrations. Each of these patients was paired with a patient from a control group.

Give two factors that should have been the same for each pair of patients and one factor that should have been different.

Doctors found:

• 4.73% of the patients who had taken medicines containing high sodium concentrations suffered from hypertension

• there were 7.18 times fewer control patients with hypertension.

Calculate how many of the control patients had hypertension.

Show your working.

A high concentration of sodium in the blood can affect blood volume and cause hypertension.

Use your knowledge of water potential to suggest how high sodium concentrations in the medicines taken could affect blood volume.

Describe the advantage of the Bohr effect during intense exercise.

A cyclist completed a fitness test on an exercise bike. The intensity of the exercise was increased every 10 seconds. The test finished when he was unable to cycle any further. The partial pressure of oxygen (pO₂) and of carbon dioxide (pCO₂) in air breathed out was measured.

Figure 3 shows the results of the cyclist’s fitness test.

Ventilatory threshold (VT) is a measure of the point when anaerobic respiration increases because aerobic respiration alone can no longer maintain muscle contraction.

VT can be identified as the first point when there is an increase in pO₂ breathed out, without an equivalent increase in pCO₂ breathed out.

Use Figure 3 to determine the time after the exercise started when the cyclist reached VT.

Calculate the ratio of pO₂ to pCO₂ in breathed-out air at this time.

Show your working.

An increase in the intensity of exercise produces an increase in the volume of carbon dioxide produced.

However, Figure 3 shows that the pCO₂ in air breathed out did not show a large increase during the exercise.

Suggest one physiological change that would cause this result. Explain how the physiological change would allow for the removal of the increase in the volume of carbon dioxide produced.

Physiological change

When muscle fibres have very low concentrations of ATP, they may get ATP in the

following ways.

• AMPK (an enzyme) oxidises fatty acids.

• Phosphocreatine donates phosphate to ADP in anaerobic conditions.

Figure 4 shows how these chemicals work.

At more than 80% of maximum muscle effort, ATP can only be made for a limited time.

Use Figure 4 to suggest one reason why.

Tick () the correct box.

GW1516 is a performance-enhancing drug. GW1516 activates AMPK and develops slow muscle fibres at rest.

Use Figure 4 to justify why professional athletes are not allowed to take GW1516.

Do not include details of chemiosmotic theory in your answer.

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood).

A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack.

Suggest how.

The normal haematocrit for human males is 47(±5)%. For professional male cyclists, the maximum haematocrit allowed is 50%.

A student suggested that professional male cyclists should be allowed to use EPO until their haematocrit is 50%.

Give two reasons why this suggestion is not valid.

Section B

one question.

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

Table 1 shows cell wall components in plants, algae, fungi and prokaryotes. Complete Table 1 by putting a tick (✓) where a cell wall component is present.

Cell walls make up much of the fibre that people eat.

Scientists investigated the relationship between the mass of fibre people ate each day and their risk of cardiovascular disease (CVD).

They gathered data from a large sample of people and used this to calculate a relative risk.

A relative risk of 1 means there is no difference in risk between the sample and the whole population.

A relative risk of < 1 means CVD is less likely to occur in the sample than in the whole population.

A relative risk of > 1 means CVD is more likely to occur in the sample than in the whole population.

Their results are shown in Figure 3. A value of ± 2 standard deviations from the mean includes over 95% of the data.

A student concluded from Figure 3 that eating an extra 10 g of fibre per day would significantly lower his risk of cardiovascular disease.

Evaluate his conclusion.

The scientists estimated the mean mass of fibre eaten per day using a food frequency questionnaire (FFQ).

The FFQ asks each person how often they have eaten many types of food over the past year.

An alternative method to calculate fibre eaten is for a nurse to ask each person detailed questions about what they have eaten in the last 24 hours.

Suggest one advantage of using the FFQ method and one disadvantage of using the FFQ method compared with the alternative method.

A scientist investigated the affinity for oxygen of horse haemoglobin and mouse haemoglobin.

Some of their results are shown in Table 7.

Plot the haemoglobin saturation data from Table 7 and use these points to sketch the full oxyhaemoglobin dissociation curves for a horse and a mouse.

The following equation can be used to estimate the metabolic rate of an animal.

BM = body mass in grams

Use this equation to calculate how many times faster the metabolic rate of a mouse is than the metabolic rate of a horse.

The data in Table 7 show differences between the oxyhaemoglobin dissociation curve for a mouse and the oxyhaemoglobin dissociation curve for a horse.

Suggest how these differences allow the mouse to have a higher metabolic rate than the horse.

Mammals such as a mouse and a horse are able to maintain a constant body temperature.

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.

Figure 2 shows a photograph of a dissected heart.

Name valve A and chamber B.

Give two safety precautions that should be followed when dissecting a heart.

Explain how valve A in Figure 2 maintains a unidirectional flow of blood.

A research scientist investigated the effect of caffeine on heart rate in human volunteers.

The scientist divided volunteers into three groups. Each group was given the same volume of fluid.

• Each member of Group I was given a sports drink containing caffeine and sugar.

• Each member of Group J was given a sports drink containing caffeine and no sugar.

• Each member of Group K was given water.

The scientist recorded the volunteers’ heart rate before the drink was given and for 120 minutes after the drink was given.

Her results can be seen in Figure 3.

Caffeine affects the autonomic nervous system.

Suggest how caffeine could account for the results of Group I in Figure 3 at 60 minutes.

Before taking the drink, the mean heart rate of Group J was 68 beats per minute.

Fifteen minutes after taking the drink, the mean volume of blood leaving the hearts of Group J was 4700 cm³ per minute.

Calculate the mean volume of blood leaving the heart at each beat fifteen minutes after taking the drink.

The increase seen in Group I could be due to the combination of caffeine and sugar.

Suggest one drink to be given to an additional group that should be investigated to find out if this is true.

Give a reason for your answer.

Group to be given

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

A haemocytometer is a special microscope slide which can be used to count the numbers of blood cells in a sample of blood.

• The surface of the slide has many small, equal-sized squares marked on it.

• The depth of the liquid under each square is 0.1 mm

• When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted.

A doctor used a haemocytometer to determine the number of red blood cells per mm in a blood sample. He diluted the original blood sample by a factor of 200 times before putting some on a haemocytometer.

Figure 4 shows the distribution of cells in a typical small square.

The doctor counted the red blood cells in many small squares. The mean number of red blood cells per small square was 7 The original blood sample was diluted by a factor of 200 times.

Calculate the number of red blood cells per mm³ in the original blood sample.

Give your answer in standard form.

When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted.

Suggest two reasons for this rule.

The doctor also wanted to know how many white blood cells per mm there were in a different sample of blood. To do this he first diluted the sample by a factor of 20 times. He then made the white blood cells clearly visible by using a stain that makes nuclei appear dark blue.

When counting white blood cells, the doctor only diluted the blood sample by a factor of 20 times, instead of 200 times when counting red blood cells.

Suggest why he only diluted the sample by a factor of 20 times.

Explain how the stain allowed the doctor to count the white blood cells amongst all the

red blood cells.

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3.

NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell.

Use your knowledge of transport across cell membranes to suggest how NHE3 does this.

Scientists investigated the use of a drug called Tenapanor to reduce salt absorption in the gut. Tenapanor inhibits the carrier protein, NHE3.

The scientists fed a diet containing a high concentration of salt to two groups of rats, A and B.

The rats in Group A were not given Tenapanor (0 mg kg^–1).

The rats in Group B were given 3 mg kg^–1 Tenapanor.

One hour after treatment, the scientists removed the gut contents of the rats and immediately weighed them.

Their results are shown in Table 2.

The scientists carried out a statistical test to see whether the difference in the means was significant. They calculated a P value of less than 0.05. They concluded that Tenapanor did reduce salt absorption in the gut.

Use all the information provided and your knowledge of water potential to explain how they reached this conclusion.

High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.

Explain how.